[PATCH net-next v3 0/7] dma: skip calling no-op sync ops when possible

[PATCH net-next v3 0/7] dma: skip calling no-op sync ops when possible

[Alexander Lobakin]

The series grew from Eric's idea and patch at [0]. The idea of using the
shortcut for direct DMA as well belongs to Chris.

When an architecture doesn't need DMA synchronization and the buffer is
not an SWIOTLB buffer, most of times the kernel and the drivers end up
calling DMA sync operations for nothing.
Even when DMA is direct, this involves a good non-inline call ladder and
eats a bunch of CPU time. With IOMMU, this results in calling indirect
calls on hotpath just to check what is already known and return.
XSk is been using a custom shortcut for that for quite some time.
I recently wanted to introduce a similar one for Page Pool. Let's combine
all this into one generic shortcut, which would cover all DMA sync ops
and all types of DMA (direct, IOMMU, ...).

* #1 adds stub inlines to be able to skip DMA sync ops or even compile
     them out when not needed.
* #2 adds the generic shortcut and enables it for direct DMA.
* #3 adds ability to skip DMA syncs behind an IOMMU.
* #4-5 are just cleanups for Page Pool to avoid merge conflicts in future.
* #6 checks for the shortcut as early as possible in the Page Pool code to
     make sure no cycles wasted.
* #7 replaces XSk's shortcut with the generic one.

On 100G NIC, the result is +3-5% for direct DMA and +10-11% for IOMMU.
As a bonus, XSk core now allows batched buffer allocations for IOMMU
setups.
If the shortcut is not available on some system, there should be no
visible performance regressions.

[0] https://lore.kernel.org/netdev/20221115182841.2640176-1-edumazet@google.com

Alexander Lobakin (7):
  dma: compile-out DMA sync op calls when not used
  dma: avoid redundant calls for sync operations
  iommu/dma: avoid expensive indirect calls for sync operations
  page_pool: make sure frag API fields don't span between cachelines
  page_pool: don't use driver-set flags field directly
  page_pool: check for DMA sync shortcut earlier
  xsk: use generic DMA sync shortcut instead of a custom one

 kernel/dma/Kconfig                            |  4 +
 include/net/page_pool/types.h                 | 21 ++++-
 include/linux/device.h                        |  5 ++
 include/linux/dma-map-ops.h                   | 21 +++++
 include/linux/dma-mapping.h                   | 84 ++++++++++++++++---
 include/net/xdp_sock_drv.h                    |  7 +-
 include/net/xsk_buff_pool.h                   | 13 +--
 drivers/base/dd.c                             |  2 +
 drivers/iommu/dma-iommu.c                     |  3 +-
 drivers/net/ethernet/engleder/tsnep_main.c    |  2 +-
 .../net/ethernet/freescale/dpaa2/dpaa2-xsk.c  |  2 +-
 drivers/net/ethernet/intel/i40e/i40e_xsk.c    |  2 +-
 drivers/net/ethernet/intel/ice/ice_xsk.c      |  2 +-
 drivers/net/ethernet/intel/igc/igc_main.c     |  2 +-
 drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c  |  2 +-
 .../ethernet/mellanox/mlx5/core/en/xsk/rx.c   |  4 +-
 .../net/ethernet/mellanox/mlx5/core/en_rx.c   |  2 +-
 drivers/net/ethernet/netronome/nfp/nfd3/xsk.c |  2 +-
 .../net/ethernet/stmicro/stmmac/stmmac_main.c |  2 +-
 kernel/dma/mapping.c                          | 59 ++++++++++---
 kernel/dma/swiotlb.c                          |  8 ++
 net/core/page_pool.c                          | 67 +++++++++------
 net/xdp/xsk_buff_pool.c                       | 29 +------
 23 files changed, 239 insertions(+), 106 deletions(-)

---
From v2[1]:
* #1:
  * use two tabs for indenting multi-line function prototypes (Chris);
* #2:
  * make shortcut clearing function generic and move it out of the
    SWIOTLB code (Chris);
  * remove dma_set_skip_sync(): use direct assignment during the initial
    setup, not used anywhere else (Chris);
  * commitmsg: remove "NIC" and the workaround paragraph (Chris).

From v1[2]:
* #1:
  * use static inlines instead of macros (Chris);
  * move CONFIG_DMA_NEED_SYNC check into dma_skip_sync() (Robin);
* #2:
  * use a new dma_map_ops flag instead of new callback, assume the same
    conditions as for direct DMA are enough (Petr, Robin);
  * add more code comments to make sure the whole idea and path are
    clear (Petr, Robin, Chris);
* #2, #3: correct the Git tags and the authorship a bit.

Not addressed in v2:
* #1:
  * dma_sync_*range_*() are still wrapped, as some subsystems may want
    to call the underscored versions directly (e.g. Page Pool);
* #2:
  * the new dev->dma_skip_sync bit is still preferred over checking for
    READ_ONCE(dev->dma_uses_io_tlb) + dev_is_dma_coherent() on hotpath
    as a faster solution.

[1] https://lore.kernel.org/netdev/20240205110426.764393-1-aleksander.lobakin@intel.com
[2] https://lore.kernel.org/netdev/20240126135456.704351-1-aleksander.lobakin@intel.com
-- 
2.43.0

[PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Alexander Lobakin]

Some platforms do have DMA, but DMA there is always direct and coherent.
Currently, even on such platforms DMA sync operations are compiled and
called.
Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
either sync operations are needed or there is DMA ops or swiotlb
enabled. Set dma_need_sync() and dma_skip_sync() depending on this
symbol state and don't call sync ops when dma_skip_sync() is true.
The change allows for future optimizations of DMA sync calls depending
on compile-time or runtime conditions.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 kernel/dma/Kconfig          |  4 ++
 include/linux/dma-mapping.h | 80 +++++++++++++++++++++++++++++++------
 kernel/dma/mapping.c        | 20 +++++-----
 3 files changed, 81 insertions(+), 23 deletions(-)

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index d62f5957f36b..1c9ff05b1ecb 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -107,6 +107,10 @@ config DMA_BOUNCE_UNALIGNED_KMALLOC
 	bool
 	depends on SWIOTLB
 
+config DMA_NEED_SYNC
+	def_bool ARCH_HAS_SYNC_DMA_FOR_DEVICE || ARCH_HAS_SYNC_DMA_FOR_CPU || \
+		 ARCH_HAS_SYNC_DMA_FOR_CPU_ALL || DMA_OPS || SWIOTLB
+
 config DMA_RESTRICTED_POOL
 	bool "DMA Restricted Pool"
 	depends on OF && OF_RESERVED_MEM && SWIOTLB
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4a658de44ee9..6c7640441214 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -117,13 +117,13 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs);
 void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
 		enum dma_data_direction dir, unsigned long attrs);
-void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
+void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
 		enum dma_data_direction dir);
-void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
+void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
 		size_t size, enum dma_data_direction dir);
-void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
 		    int nelems, enum dma_data_direction dir);
-void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 		       int nelems, enum dma_data_direction dir);
 void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		gfp_t flag, unsigned long attrs);
@@ -147,7 +147,7 @@ u64 dma_get_required_mask(struct device *dev);
 bool dma_addressing_limited(struct device *dev);
 size_t dma_max_mapping_size(struct device *dev);
 size_t dma_opt_mapping_size(struct device *dev);
-bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
+bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr);
 unsigned long dma_get_merge_boundary(struct device *dev);
 struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
 		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs);
@@ -195,19 +195,19 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
 {
 }
-static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
-		size_t size, enum dma_data_direction dir)
+static inline void __dma_sync_single_for_cpu(struct device *dev,
+		dma_addr_t addr, size_t size, enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_single_for_device(struct device *dev,
+static inline void __dma_sync_single_for_device(struct device *dev,
 		dma_addr_t addr, size_t size, enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_sg_for_cpu(struct device *dev,
+static inline void __dma_sync_sg_for_cpu(struct device *dev,
 		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
 {
 }
-static inline void dma_sync_sg_for_device(struct device *dev,
+static inline void __dma_sync_sg_for_device(struct device *dev,
 		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
 {
 }
@@ -277,7 +277,7 @@ static inline size_t dma_opt_mapping_size(struct device *dev)
 {
 	return 0;
 }
-static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
+static inline bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 {
 	return false;
 }
@@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
 	return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
 }
 
+static inline void __dma_sync_single_range_for_cpu(struct device *dev,
+		dma_addr_t addr, unsigned long offset, size_t size,
+		enum dma_data_direction dir)
+{
+	__dma_sync_single_for_cpu(dev, addr + offset, size, dir);
+}
+
+static inline void __dma_sync_single_range_for_device(struct device *dev,
+		dma_addr_t addr, unsigned long offset, size_t size,
+		enum dma_data_direction dir)
+{
+	__dma_sync_single_for_device(dev, addr + offset, size, dir);
+}
+
+static inline bool dma_skip_sync(const struct device *dev)
+{
+	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
+}
+
+static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
+{
+	return !dma_skip_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
+}
+
+static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
+		size_t size, enum dma_data_direction dir)
+{
+	if (!dma_skip_sync(dev))
+		__dma_sync_single_for_cpu(dev, addr, size, dir);
+}
+
+static inline void dma_sync_single_for_device(struct device *dev,
+		dma_addr_t addr, size_t size, enum dma_data_direction dir)
+{
+	if (!dma_skip_sync(dev))
+		__dma_sync_single_for_device(dev, addr, size, dir);
+}
+
+static inline void dma_sync_sg_for_cpu(struct device *dev,
+		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+{
+	if (!dma_skip_sync(dev))
+		__dma_sync_sg_for_cpu(dev, sg, nelems, dir);
+}
+
+static inline void dma_sync_sg_for_device(struct device *dev,
+		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
+{
+	if (!dma_skip_sync(dev))
+		__dma_sync_sg_for_device(dev, sg, nelems, dir);
+}
+
 static inline void dma_sync_single_range_for_cpu(struct device *dev,
 		dma_addr_t addr, unsigned long offset, size_t size,
 		enum dma_data_direction dir)
 {
-	return dma_sync_single_for_cpu(dev, addr + offset, size, dir);
+	if (!dma_skip_sync(dev))
+		__dma_sync_single_for_cpu(dev, addr + offset, size, dir);
 }
 
 static inline void dma_sync_single_range_for_device(struct device *dev,
 		dma_addr_t addr, unsigned long offset, size_t size,
 		enum dma_data_direction dir)
 {
-	return dma_sync_single_for_device(dev, addr + offset, size, dir);
+	if (!dma_skip_sync(dev))
+		__dma_sync_single_for_device(dev, addr + offset, size, dir);
 }
 
 /**
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 58db8fd70471..85feaa0e008c 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -329,7 +329,7 @@ void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
 }
 EXPORT_SYMBOL(dma_unmap_resource);
 
-void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
+void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
 		enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -341,9 +341,9 @@ void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
 		ops->sync_single_for_cpu(dev, addr, size, dir);
 	debug_dma_sync_single_for_cpu(dev, addr, size, dir);
 }
-EXPORT_SYMBOL(dma_sync_single_for_cpu);
+EXPORT_SYMBOL(__dma_sync_single_for_cpu);
 
-void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
+void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
 		size_t size, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -355,9 +355,9 @@ void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
 		ops->sync_single_for_device(dev, addr, size, dir);
 	debug_dma_sync_single_for_device(dev, addr, size, dir);
 }
-EXPORT_SYMBOL(dma_sync_single_for_device);
+EXPORT_SYMBOL(__dma_sync_single_for_device);
 
-void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
 		    int nelems, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -369,9 +369,9 @@ void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
 		ops->sync_sg_for_cpu(dev, sg, nelems, dir);
 	debug_dma_sync_sg_for_cpu(dev, sg, nelems, dir);
 }
-EXPORT_SYMBOL(dma_sync_sg_for_cpu);
+EXPORT_SYMBOL(__dma_sync_sg_for_cpu);
 
-void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
+void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 		       int nelems, enum dma_data_direction dir)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -383,7 +383,7 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
 		ops->sync_sg_for_device(dev, sg, nelems, dir);
 	debug_dma_sync_sg_for_device(dev, sg, nelems, dir);
 }
-EXPORT_SYMBOL(dma_sync_sg_for_device);
+EXPORT_SYMBOL(__dma_sync_sg_for_device);
 
 /*
  * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems
@@ -841,7 +841,7 @@ size_t dma_opt_mapping_size(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(dma_opt_mapping_size);
 
-bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
+bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
@@ -849,7 +849,7 @@ bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 		return dma_direct_need_sync(dev, dma_addr);
 	return ops->sync_single_for_cpu || ops->sync_single_for_device;
 }
-EXPORT_SYMBOL_GPL(dma_need_sync);
+EXPORT_SYMBOL_GPL(__dma_need_sync);
 
 unsigned long dma_get_merge_boundary(struct device *dev)
 {
-- 
2.43.0

[PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Alexander Lobakin]

Quite often, devices do not need dma_sync operations on x86_64 at least.
Indeed, when dev_is_dma_coherent(dev) is true and
dev_use_swiotlb(dev) is false, iommu_dma_sync_single_for_cpu()
and friends do nothing.

However, indirectly calling them when CONFIG_RETPOLINE=y consumes about
10% of cycles on a cpu receiving packets from softirq at ~100Gbit rate.
Even if/when CONFIG_RETPOLINE is not set, there is a cost of about 3%.

Add dev->skip_dma_sync boolean which is set during the device
initialization depending on the setup: dev_is_dma_coherent() for the
direct DMA, !(sync_single_for_device || sync_single_for_cpu) or the new
dma_map_ops flag, %DMA_F_CAN_SKIP_SYNC, advertised for non-NULL DMA ops.
Then later, if/when swiotlb is used for the first time, the flag
is turned off, from swiotlb_tbl_map_single().

On iavf, the UDP trafficgen with XDP_DROP in skb mode test shows
+3-5% increase for direct DMA.

Suggested-by: Christoph Hellwig <hch@lst.de> # direct DMA shortcut
Co-developed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 include/linux/device.h      |  5 +++++
 include/linux/dma-map-ops.h | 21 ++++++++++++++++++++
 include/linux/dma-mapping.h |  6 +++++-
 drivers/base/dd.c           |  2 ++
 kernel/dma/mapping.c        | 39 ++++++++++++++++++++++++++++++++++++-
 kernel/dma/swiotlb.c        |  8 ++++++++
 6 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/include/linux/device.h b/include/linux/device.h
index 97c4b046c09d..f23e6a32bea0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -686,6 +686,8 @@ struct device_physical_location {
  *		other devices probe successfully.
  * @dma_coherent: this particular device is dma coherent, even if the
  *		architecture supports non-coherent devices.
+ * @dma_skip_sync: DMA sync operations can be skipped for coherent non-SWIOTLB
+ *		buffers.
  * @dma_ops_bypass: If set to %true then the dma_ops are bypassed for the
  *		streaming DMA operations (->map_* / ->unmap_* / ->sync_*),
  *		and optionall (if the coherent mask is large enough) also
@@ -800,6 +802,9 @@ struct device {
     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
 	bool			dma_coherent:1;
 #endif
+#ifdef CONFIG_DMA_NEED_SYNC
+	bool			dma_skip_sync:1;
+#endif
 #ifdef CONFIG_DMA_OPS_BYPASS
 	bool			dma_ops_bypass : 1;
 #endif
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 4abc60f04209..327b73f653ad 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -18,8 +18,11 @@ struct iommu_ops;
  *
  * DMA_F_PCI_P2PDMA_SUPPORTED: Indicates the dma_map_ops implementation can
  * handle PCI P2PDMA pages in the map_sg/unmap_sg operation.
+ * DMA_F_CAN_SKIP_SYNC: DMA sync operations can be skipped if the device is
+ * coherent and it's not an SWIOTLB buffer.
  */
 #define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
+#define DMA_F_CAN_SKIP_SYNC		BIT(1)
 
 struct dma_map_ops {
 	unsigned int flags;
@@ -111,6 +114,24 @@ static inline void set_dma_ops(struct device *dev,
 }
 #endif /* CONFIG_DMA_OPS */
 
+#ifdef CONFIG_DMA_NEED_SYNC
+void dma_setup_skip_sync(struct device *dev);
+
+static inline void dma_clear_skip_sync(struct device *dev)
+{
+	/* Clear it only once so that the function can be called on hotpath */
+	if (unlikely(dev->dma_skip_sync))
+		dev->dma_skip_sync = false;
+}
+#else /* !CONFIG_DMA_NEED_SYNC */
+static inline void dma_setup_skip_sync(struct device *dev)
+{
+}
+static inline void dma_clear_skip_sync(struct device *dev)
+{
+}
+#endif /* !CONFIG_DMA_NEED_SYNC */
+
 #ifdef CONFIG_DMA_CMA
 extern struct cma *dma_contiguous_default_area;
 
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 6c7640441214..d85ae541c267 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -364,7 +364,11 @@ static inline void __dma_sync_single_range_for_device(struct device *dev,
 
 static inline bool dma_skip_sync(const struct device *dev)
 {
-	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
+#ifdef CONFIG_DMA_NEED_SYNC
+	return dev->dma_skip_sync;
+#else
+	return true;
+#endif
 }
 
 static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 85152537dbf1..67ad3e1d51f6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -642,6 +642,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 			goto pinctrl_bind_failed;
 	}
 
+	dma_setup_skip_sync(dev);
+
 	ret = driver_sysfs_add(dev);
 	if (ret) {
 		pr_err("%s: driver_sysfs_add(%s) failed\n",
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 85feaa0e008c..5f588e31ea89 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -846,8 +846,14 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
 	if (dma_map_direct(dev, ops))
+		/*
+		 * dma_skip_sync could've been set to false on first SWIOTLB
+		 * buffer mapping, but @dma_addr is not necessary an SWIOTLB
+		 * buffer. In this case, fall back to more granular check.
+		 */
 		return dma_direct_need_sync(dev, dma_addr);
-	return ops->sync_single_for_cpu || ops->sync_single_for_device;
+
+	return true;
 }
 EXPORT_SYMBOL_GPL(__dma_need_sync);
 
@@ -861,3 +867,34 @@ unsigned long dma_get_merge_boundary(struct device *dev)
 	return ops->get_merge_boundary(dev);
 }
 EXPORT_SYMBOL_GPL(dma_get_merge_boundary);
+
+#ifdef CONFIG_DMA_NEED_SYNC
+void dma_setup_skip_sync(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (dma_map_direct(dev, ops))
+		/*
+		 * dma_skip_sync will be set to false on first SWIOTLB buffer
+		 * mapping, if any. During the device initialization, it's
+		 * enough to check only for DMA coherence.
+		 */
+		dev->dma_skip_sync = dev_is_dma_coherent(dev);
+	else if (!ops->sync_single_for_device && !ops->sync_single_for_cpu)
+		/*
+		 * Synchronization is not possible when none of DMA sync ops
+		 * is set. This check precedes the below one as it disables
+		 * the synchronization unconditionally.
+		 */
+		dev->dma_skip_sync = true;
+	else if (ops->flags & DMA_F_CAN_SKIP_SYNC)
+		/*
+		 * Assume that when ``DMA_F_CAN_SKIP_SYNC`` is advertised,
+		 * the conditions for synchronizing are the same as with
+		 * the direct DMA.
+		 */
+		dev->dma_skip_sync = dev_is_dma_coherent(dev);
+	else
+		dev->dma_skip_sync = false;
+}
+#endif /* CONFIG_DMA_NEED_SYNC */
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index b079a9a8e087..0b737eab4d48 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1323,6 +1323,12 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
 		return (phys_addr_t)DMA_MAPPING_ERROR;
 	}
 
+	/*
+	 * If dma_skip_sync was set, reset it to false on first SWIOTLB buffer
+	 * mapping to always sync SWIOTLB buffers.
+	 */
+	dma_clear_skip_sync(dev);
+
 	/*
 	 * Save away the mapping from the original address to the DMA address.
 	 * This is needed when we sync the memory.  Then we sync the buffer if
@@ -1640,6 +1646,8 @@ struct page *swiotlb_alloc(struct device *dev, size_t size)
 	if (index == -1)
 		return NULL;
 
+	dma_clear_skip_sync(dev);
+
 	tlb_addr = slot_addr(pool->start, index);
 
 	return pfn_to_page(PFN_DOWN(tlb_addr));
-- 
2.43.0

[PATCH net-next v3 3/7] iommu/dma: avoid expensive indirect calls for sync operations

[Alexander Lobakin]

When IOMMU is on, the actual synchronization happens in the same cases
as with the direct DMA. Advertise %DMA_F_CAN_SKIP_SYNC in IOMMU DMA to
skip sync ops calls (indirect) for non-SWIOTLB buffers.

perf profile before the patch:

    18.53%  [kernel]       [k] gq_rx_skb
    14.77%  [kernel]       [k] napi_reuse_skb
     8.95%  [kernel]       [k] skb_release_data
     5.42%  [kernel]       [k] dev_gro_receive
     5.37%  [kernel]       [k] memcpy
<*>  5.26%  [kernel]       [k] iommu_dma_sync_sg_for_cpu
     4.78%  [kernel]       [k] tcp_gro_receive
<*>  4.42%  [kernel]       [k] iommu_dma_sync_sg_for_device
     4.12%  [kernel]       [k] ipv6_gro_receive
     3.65%  [kernel]       [k] gq_pool_get
     3.25%  [kernel]       [k] skb_gro_receive
     2.07%  [kernel]       [k] napi_gro_frags
     1.98%  [kernel]       [k] tcp6_gro_receive
     1.27%  [kernel]       [k] gq_rx_prep_buffers
     1.18%  [kernel]       [k] gq_rx_napi_handler
     0.99%  [kernel]       [k] csum_partial
     0.74%  [kernel]       [k] csum_ipv6_magic
     0.72%  [kernel]       [k] free_pcp_prepare
     0.60%  [kernel]       [k] __napi_poll
     0.58%  [kernel]       [k] net_rx_action
     0.56%  [kernel]       [k] read_tsc
<*>  0.50%  [kernel]       [k] __x86_indirect_thunk_r11
     0.45%  [kernel]       [k] memset

After patch, lines with <*> no longer show up, and overall
cpu usage looks much better (~60% instead of ~72%):

    25.56%  [kernel]       [k] gq_rx_skb
     9.90%  [kernel]       [k] napi_reuse_skb
     7.39%  [kernel]       [k] dev_gro_receive
     6.78%  [kernel]       [k] memcpy
     6.53%  [kernel]       [k] skb_release_data
     6.39%  [kernel]       [k] tcp_gro_receive
     5.71%  [kernel]       [k] ipv6_gro_receive
     4.35%  [kernel]       [k] napi_gro_frags
     4.34%  [kernel]       [k] skb_gro_receive
     3.50%  [kernel]       [k] gq_pool_get
     3.08%  [kernel]       [k] gq_rx_napi_handler
     2.35%  [kernel]       [k] tcp6_gro_receive
     2.06%  [kernel]       [k] gq_rx_prep_buffers
     1.32%  [kernel]       [k] csum_partial
     0.93%  [kernel]       [k] csum_ipv6_magic
     0.65%  [kernel]       [k] net_rx_action

iavf yields +10% of Mpps on Rx. This also unblocks batched allocations
of XSk buffers when IOMMU is active.

Co-developed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 drivers/iommu/dma-iommu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 50ccc4f1ef81..4ab9ac13d362 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1707,7 +1707,8 @@ static size_t iommu_dma_opt_mapping_size(void)
 }
 
 static const struct dma_map_ops iommu_dma_ops = {
-	.flags			= DMA_F_PCI_P2PDMA_SUPPORTED,
+	.flags			= DMA_F_PCI_P2PDMA_SUPPORTED |
+				  DMA_F_CAN_SKIP_SYNC,
 	.alloc			= iommu_dma_alloc,
 	.free			= iommu_dma_free,
 	.alloc_pages		= dma_common_alloc_pages,
-- 
2.43.0

[PATCH net-next v3 4/7] page_pool: make sure frag API fields don't span between cachelines

[Alexander Lobakin]

After commit 5027ec19f104 ("net: page_pool: split the page_pool_params
into fast and slow") that made &page_pool contain only "hot" params at
the start, cacheline boundary chops frag API fields group in the middle
again.
To not bother with this each time fast params get expanded or shrunk,
let's just align them to `4 * sizeof(long)`, the closest upper pow-2 to
their actual size (2 longs + 1 int). This ensures 16-byte alignment for
the 32-bit architectures and 32-byte alignment for the 64-bit ones,
excluding unnecessary false-sharing.
::page_state_hold_cnt is used quite intensively on hotpath no matter if
frag API is used, so move it to the newly created hole in the first
cacheline.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 include/net/page_pool/types.h | 12 +++++++++++-
 net/core/page_pool.c          |  9 +++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
index 3828396ae60c..b2b93bec7bce 100644
--- a/include/net/page_pool/types.h
+++ b/include/net/page_pool/types.h
@@ -129,12 +129,22 @@ struct page_pool {
 	struct page_pool_params_fast p;
 
 	int cpuid;
+	u32 pages_state_hold_cnt;
 	bool has_init_callback;
 
+	/* The following block must stay within one cacheline. On 32-bit
+	 * systems, sizeof(long) == sizeof(int), so that the block size is
+	 * ``3 * sizeof(long)``. On 64-bit systems, the actual size is
+	 * ``2 * sizeof(long) + sizeof(int)``. The closest pow-2 to both of
+	 * them is ``4 * sizeof(long)``, so just use that one for simplicity.
+	 * Having it aligned to a cacheline boundary may be excessive and
+	 * doesn't bring any good.
+	 */
+	__cacheline_group_begin(frag) __aligned(4 * sizeof(long));
 	long frag_users;
 	struct page *frag_page;
 	unsigned int frag_offset;
-	u32 pages_state_hold_cnt;
+	__cacheline_group_end(frag);
 
 	struct delayed_work release_dw;
 	void (*disconnect)(void *pool);
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 89c835fcf094..3c464852e228 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -170,12 +170,21 @@ static void page_pool_producer_unlock(struct page_pool *pool,
 		spin_unlock_bh(&pool->ring.producer_lock);
 }
 
+static void page_pool_struct_check(void)
+{
+	CACHELINE_ASSERT_GROUP_MEMBER(struct page_pool, frag, frag_users);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct page_pool, frag, frag_page);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct page_pool, frag, frag_offset);
+}
+
 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params,
 			  int cpuid)
 {
 	unsigned int ring_qsize = 1024; /* Default */
 
+	page_pool_struct_check();
+
 	memcpy(&pool->p, &params->fast, sizeof(pool->p));
 	memcpy(&pool->slow, &params->slow, sizeof(pool->slow));
 
-- 
2.43.0

[PATCH net-next v3 5/7] page_pool: don't use driver-set flags field directly

[Alexander Lobakin]

page_pool::p is driver-defined params, copied directly from the
structure passed to page_pool_create(). The structure isn't meant
to be modified by the Page Pool core code and this even might look
confusing[0][1].
In order to be able to alter some flags, let's define our own, internal
fields the same way as the already existing one (::has_init_callback).
They are defined as bits in the driver-set params, leave them so here
as well, to not waste byte-per-bit or so. Almost 30 bits are still free
for future extensions.
We could've defined only new flags here or only the ones we may need
to alter, but checking some flags in one place while others in another
doesn't sound convenient or intuitive. ::flags passed by the driver can
now go to the "slow" PP params.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Link[0]: https://lore.kernel.org/netdev/20230703133207.4f0c54ce@kernel.org
Suggested-by: Alexander Duyck <alexanderduyck@fb.com>
Link[1]: https://lore.kernel.org/netdev/CAKgT0UfZCGnWgOH96E4GV3ZP6LLbROHM7SHE8NKwq+exX+Gk_Q@mail.gmail.com
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 include/net/page_pool/types.h |  9 ++++++---
 net/core/page_pool.c          | 34 ++++++++++++++++++----------------
 2 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
index b2b93bec7bce..938980dafa7d 100644
--- a/include/net/page_pool/types.h
+++ b/include/net/page_pool/types.h
@@ -44,7 +44,6 @@ struct pp_alloc_cache {
 
 /**
  * struct page_pool_params - page pool parameters
- * @flags:	PP_FLAG_DMA_MAP, PP_FLAG_DMA_SYNC_DEV
  * @order:	2^order pages on allocation
  * @pool_size:	size of the ptr_ring
  * @nid:	NUMA node id to allocate from pages from
@@ -54,10 +53,10 @@ struct pp_alloc_cache {
  * @dma_dir:	DMA mapping direction
  * @max_len:	max DMA sync memory size for PP_FLAG_DMA_SYNC_DEV
  * @offset:	DMA sync address offset for PP_FLAG_DMA_SYNC_DEV
+ * @flags:	PP_FLAG_DMA_MAP, PP_FLAG_DMA_SYNC_DEV
  */
 struct page_pool_params {
 	struct_group_tagged(page_pool_params_fast, fast,
-		unsigned int	flags;
 		unsigned int	order;
 		unsigned int	pool_size;
 		int		nid;
@@ -68,6 +67,7 @@ struct page_pool_params {
 		unsigned int	offset;
 	);
 	struct_group_tagged(page_pool_params_slow, slow,
+		unsigned int	flags;
 		struct net_device *netdev;
 /* private: used by test code only */
 		void (*init_callback)(struct page *page, void *arg);
@@ -130,7 +130,10 @@ struct page_pool {
 
 	int cpuid;
 	u32 pages_state_hold_cnt;
-	bool has_init_callback;
+
+	bool dma_map:1;			/* Perform DMA mapping */
+	bool dma_sync:1;		/* Perform DMA sync */
+	bool has_init_callback:1;	/* slow.init_callback is set */
 
 	/* The following block must stay within one cacheline. On 32-bit
 	 * systems, sizeof(long) == sizeof(int), so that the block size is
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 3c464852e228..a9f3c032c45f 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -191,7 +191,7 @@ static int page_pool_init(struct page_pool *pool,
 	pool->cpuid = cpuid;
 
 	/* Validate only known flags were used */
-	if (pool->p.flags & ~(PP_FLAG_ALL))
+	if (pool->slow.flags & ~(PP_FLAG_ALL))
 		return -EINVAL;
 
 	if (pool->p.pool_size)
@@ -205,22 +205,26 @@ static int page_pool_init(struct page_pool *pool,
 	 * DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
 	 * which is the XDP_TX use-case.
 	 */
-	if (pool->p.flags & PP_FLAG_DMA_MAP) {
+	if (pool->slow.flags & PP_FLAG_DMA_MAP) {
 		if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
 		    (pool->p.dma_dir != DMA_BIDIRECTIONAL))
 			return -EINVAL;
+
+		pool->dma_map = true;
 	}
 
-	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) {
+	if (pool->slow.flags & PP_FLAG_DMA_SYNC_DEV) {
 		/* In order to request DMA-sync-for-device the page
 		 * needs to be mapped
 		 */
-		if (!(pool->p.flags & PP_FLAG_DMA_MAP))
+		if (!(pool->slow.flags & PP_FLAG_DMA_MAP))
 			return -EINVAL;
 
 		if (!pool->p.max_len)
 			return -EINVAL;
 
+		pool->dma_sync = true;
+
 		/* pool->p.offset has to be set according to the address
 		 * offset used by the DMA engine to start copying rx data
 		 */
@@ -246,7 +250,7 @@ static int page_pool_init(struct page_pool *pool,
 	/* Driver calling page_pool_create() also call page_pool_destroy() */
 	refcount_set(&pool->user_cnt, 1);
 
-	if (pool->p.flags & PP_FLAG_DMA_MAP)
+	if (pool->dma_map)
 		get_device(pool->p.dev);
 
 	return 0;
@@ -256,7 +260,7 @@ static void page_pool_uninit(struct page_pool *pool)
 {
 	ptr_ring_cleanup(&pool->ring, NULL);
 
-	if (pool->p.flags & PP_FLAG_DMA_MAP)
+	if (pool->dma_map)
 		put_device(pool->p.dev);
 
 #ifdef CONFIG_PAGE_POOL_STATS
@@ -411,7 +415,7 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	if (page_pool_set_dma_addr(page, dma))
 		goto unmap_failed;
 
-	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+	if (pool->dma_sync)
 		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
 
 	return true;
@@ -457,8 +461,7 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
 	if (unlikely(!page))
 		return NULL;
 
-	if ((pool->p.flags & PP_FLAG_DMA_MAP) &&
-	    unlikely(!page_pool_dma_map(pool, page))) {
+	if (pool->dma_map && unlikely(!page_pool_dma_map(pool, page))) {
 		put_page(page);
 		return NULL;
 	}
@@ -478,8 +481,8 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 						 gfp_t gfp)
 {
 	const int bulk = PP_ALLOC_CACHE_REFILL;
-	unsigned int pp_flags = pool->p.flags;
 	unsigned int pp_order = pool->p.order;
+	bool dma_map = pool->dma_map;
 	struct page *page;
 	int i, nr_pages;
 
@@ -504,8 +507,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	 */
 	for (i = 0; i < nr_pages; i++) {
 		page = pool->alloc.cache[i];
-		if ((pp_flags & PP_FLAG_DMA_MAP) &&
-		    unlikely(!page_pool_dma_map(pool, page))) {
+		if (dma_map && unlikely(!page_pool_dma_map(pool, page))) {
 			put_page(page);
 			continue;
 		}
@@ -577,7 +579,7 @@ void __page_pool_release_page_dma(struct page_pool *pool, struct page *page)
 {
 	dma_addr_t dma;
 
-	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
+	if (!pool->dma_map)
 		/* Always account for inflight pages, even if we didn't
 		 * map them
 		 */
@@ -655,7 +657,7 @@ static bool page_pool_recycle_in_cache(struct page *page,
 }
 
 /* If the page refcnt == 1, this will try to recycle the page.
- * if PP_FLAG_DMA_SYNC_DEV is set, we'll try to sync the DMA area for
+ * If pool->dma_sync is set, we'll try to sync the DMA area for
  * the configured size min(dma_sync_size, pool->max_len).
  * If the page refcnt != 1, then the page will be returned to memory
  * subsystem.
@@ -678,7 +680,7 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
 	if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page))) {
 		/* Read barrier done in page_ref_count / READ_ONCE */
 
-		if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+		if (pool->dma_sync)
 			page_pool_dma_sync_for_device(pool, page,
 						      dma_sync_size);
 
@@ -791,7 +793,7 @@ static struct page *page_pool_drain_frag(struct page_pool *pool,
 		return NULL;
 
 	if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
-		if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+		if (pool->dma_sync)
 			page_pool_dma_sync_for_device(pool, page, -1);
 
 		return page;
-- 
2.43.0

[PATCH net-next v3 6/7] page_pool: check for DMA sync shortcut earlier

[Alexander Lobakin]

We can save a couple more function calls in the Page Pool code if we
check for dma_skip_sync() earlier, just when we test pp->p.dma_sync.
Move both these checks into an inline wrapper and call the PP wrapper
over the generic DMA sync function only when both are true.
You can't cache the result of dma_skip_sync() in &page_pool, as it may
change anytime if an SWIOTLB buffer is allocated or mapped.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 net/core/page_pool.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index a9f3c032c45f..a48895d824e2 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -384,16 +384,24 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
 	return page;
 }
 
-static void page_pool_dma_sync_for_device(struct page_pool *pool,
-					  struct page *page,
-					  unsigned int dma_sync_size)
+static void __page_pool_dma_sync_for_device(struct page_pool *pool,
+					    struct page *page,
+					    u32 dma_sync_size)
 {
 	dma_addr_t dma_addr = page_pool_get_dma_addr(page);
 
 	dma_sync_size = min(dma_sync_size, pool->p.max_len);
-	dma_sync_single_range_for_device(pool->p.dev, dma_addr,
-					 pool->p.offset, dma_sync_size,
-					 pool->p.dma_dir);
+	__dma_sync_single_range_for_device(pool->p.dev, dma_addr,
+					   pool->p.offset, dma_sync_size,
+					   pool->p.dma_dir);
+}
+
+static __always_inline void
+page_pool_dma_sync_for_device(struct page_pool *pool, struct page *page,
+			      u32 dma_sync_size)
+{
+	if (pool->dma_sync && !dma_skip_sync(pool->p.dev))
+		__page_pool_dma_sync_for_device(pool, page, dma_sync_size);
 }
 
 static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
@@ -415,8 +423,7 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	if (page_pool_set_dma_addr(page, dma))
 		goto unmap_failed;
 
-	if (pool->dma_sync)
-		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
+	page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
 
 	return true;
 
@@ -680,9 +687,7 @@ __page_pool_put_page(struct page_pool *pool, struct page *page,
 	if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page))) {
 		/* Read barrier done in page_ref_count / READ_ONCE */
 
-		if (pool->dma_sync)
-			page_pool_dma_sync_for_device(pool, page,
-						      dma_sync_size);
+		page_pool_dma_sync_for_device(pool, page, dma_sync_size);
 
 		if (allow_direct && in_softirq() &&
 		    page_pool_recycle_in_cache(page, pool))
@@ -793,8 +798,7 @@ static struct page *page_pool_drain_frag(struct page_pool *pool,
 		return NULL;
 
 	if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
-		if (pool->dma_sync)
-			page_pool_dma_sync_for_device(pool, page, -1);
+		page_pool_dma_sync_for_device(pool, page, -1);
 
 		return page;
 	}
-- 
2.43.0

[PATCH net-next v3 7/7] xsk: use generic DMA sync shortcut instead of a custom one

[Alexander Lobakin]

XSk infra's been using its own DMA sync shortcut to try avoiding
redundant function calls. Now that there is a generic one, remove
the custom implementation and rely on the generic helpers.
xsk_buff_dma_sync_for_cpu() doesn't need the second argument anymore,
remove it.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 include/net/xdp_sock_drv.h                    |  7 ++---
 include/net/xsk_buff_pool.h                   | 13 ++-------
 drivers/net/ethernet/engleder/tsnep_main.c    |  2 +-
 .../net/ethernet/freescale/dpaa2/dpaa2-xsk.c  |  2 +-
 drivers/net/ethernet/intel/i40e/i40e_xsk.c    |  2 +-
 drivers/net/ethernet/intel/ice/ice_xsk.c      |  2 +-
 drivers/net/ethernet/intel/igc/igc_main.c     |  2 +-
 drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c  |  2 +-
 .../ethernet/mellanox/mlx5/core/en/xsk/rx.c   |  4 +--
 .../net/ethernet/mellanox/mlx5/core/en_rx.c   |  2 +-
 drivers/net/ethernet/netronome/nfp/nfd3/xsk.c |  2 +-
 .../net/ethernet/stmicro/stmmac/stmmac_main.c |  2 +-
 net/xdp/xsk_buff_pool.c                       | 29 +++----------------
 13 files changed, 20 insertions(+), 51 deletions(-)

diff --git a/include/net/xdp_sock_drv.h b/include/net/xdp_sock_drv.h
index c9aec9ab6191..0a5dca2b2b3f 100644
--- a/include/net/xdp_sock_drv.h
+++ b/include/net/xdp_sock_drv.h
@@ -219,13 +219,10 @@ static inline struct xsk_tx_metadata *xsk_buff_get_metadata(struct xsk_buff_pool
 	return meta;
 }
 
-static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp, struct xsk_buff_pool *pool)
+static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp)
 {
 	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
 
-	if (!pool->dma_need_sync)
-		return;
-
 	xp_dma_sync_for_cpu(xskb);
 }
 
@@ -402,7 +399,7 @@ static inline struct xsk_tx_metadata *xsk_buff_get_metadata(struct xsk_buff_pool
 	return NULL;
 }
 
-static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp, struct xsk_buff_pool *pool)
+static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp)
 {
 }
 
diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index 99dd7376df6a..b61e787a0ee5 100644
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -43,7 +43,6 @@ struct xsk_dma_map {
 	refcount_t users;
 	struct list_head list; /* Protected by the RTNL_LOCK */
 	u32 dma_pages_cnt;
-	bool dma_need_sync;
 };
 
 struct xsk_buff_pool {
@@ -82,7 +81,6 @@ struct xsk_buff_pool {
 	u8 tx_metadata_len; /* inherited from umem */
 	u8 cached_need_wakeup;
 	bool uses_need_wakeup;
-	bool dma_need_sync;
 	bool unaligned;
 	bool tx_sw_csum;
 	void *addrs;
@@ -155,21 +153,16 @@ static inline dma_addr_t xp_get_frame_dma(struct xdp_buff_xsk *xskb)
 	return xskb->frame_dma;
 }
 
-void xp_dma_sync_for_cpu_slow(struct xdp_buff_xsk *xskb);
 static inline void xp_dma_sync_for_cpu(struct xdp_buff_xsk *xskb)
 {
-	xp_dma_sync_for_cpu_slow(xskb);
+	dma_sync_single_for_cpu(xskb->pool->dev, xskb->dma,
+				xskb->pool->frame_len, DMA_BIDIRECTIONAL);
 }
 
-void xp_dma_sync_for_device_slow(struct xsk_buff_pool *pool, dma_addr_t dma,
-				 size_t size);
 static inline void xp_dma_sync_for_device(struct xsk_buff_pool *pool,
 					  dma_addr_t dma, size_t size)
 {
-	if (!pool->dma_need_sync)
-		return;
-
-	xp_dma_sync_for_device_slow(pool, dma, size);
+	dma_sync_single_for_device(pool->dev, dma, size, DMA_BIDIRECTIONAL);
 }
 
 /* Masks for xdp_umem_page flags.
diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
index 4b15af6b7122..44da335d66bd 100644
--- a/drivers/net/ethernet/engleder/tsnep_main.c
+++ b/drivers/net/ethernet/engleder/tsnep_main.c
@@ -1587,7 +1587,7 @@ static int tsnep_rx_poll_zc(struct tsnep_rx *rx, struct napi_struct *napi,
 		length = __le32_to_cpu(entry->desc_wb->properties) &
 			 TSNEP_DESC_LENGTH_MASK;
 		xsk_buff_set_size(entry->xdp, length - ETH_FCS_LEN);
-		xsk_buff_dma_sync_for_cpu(entry->xdp, rx->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(entry->xdp);
 
 		/* RX metadata with timestamps is in front of actual data,
 		 * subtract metadata size to get length of actual data and
diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
index 051748b997f3..a466c2379146 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
@@ -55,7 +55,7 @@ static u32 dpaa2_xsk_run_xdp(struct dpaa2_eth_priv *priv,
 	xdp_set_data_meta_invalid(xdp_buff);
 	xdp_buff->rxq = &ch->xdp_rxq;
 
-	xsk_buff_dma_sync_for_cpu(xdp_buff, ch->xsk_pool);
+	xsk_buff_dma_sync_for_cpu(xdp_buff);
 	xdp_act = bpf_prog_run_xdp(xdp_prog, xdp_buff);
 
 	/* xdp.data pointer may have changed */
diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
index 11500003af0d..d20ce517426e 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
@@ -483,7 +483,7 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 
 		bi = *i40e_rx_bi(rx_ring, next_to_process);
 		xsk_buff_set_size(bi, size);
-		xsk_buff_dma_sync_for_cpu(bi, rx_ring->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(bi);
 
 		if (!first)
 			first = bi;
diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
index 8a051420fa19..0d3d56aca424 100644
--- a/drivers/net/ethernet/intel/ice/ice_xsk.c
+++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
@@ -878,7 +878,7 @@ int ice_clean_rx_irq_zc(struct ice_rx_ring *rx_ring, int budget)
 				   ICE_RX_FLX_DESC_PKT_LEN_M;
 
 		xsk_buff_set_size(xdp, size);
-		xsk_buff_dma_sync_for_cpu(xdp, xsk_pool);
+		xsk_buff_dma_sync_for_cpu(xdp);
 
 		if (!first) {
 			first = xdp;
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index c3fe62813f43..6e3ce15053b1 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2817,7 +2817,7 @@ static int igc_clean_rx_irq_zc(struct igc_q_vector *q_vector, const int budget)
 		}
 
 		bi->xdp->data_end = bi->xdp->data + size;
-		xsk_buff_dma_sync_for_cpu(bi->xdp, ring->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(bi->xdp);
 
 		res = __igc_xdp_run_prog(adapter, prog, bi->xdp);
 		switch (res) {
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
index 59798bc33298..ebda0cebe910 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
@@ -304,7 +304,7 @@ int ixgbe_clean_rx_irq_zc(struct ixgbe_q_vector *q_vector,
 		}
 
 		bi->xdp->data_end = bi->xdp->data + size;
-		xsk_buff_dma_sync_for_cpu(bi->xdp, rx_ring->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(bi->xdp);
 		xdp_res = ixgbe_run_xdp_zc(adapter, rx_ring, bi->xdp);
 
 		if (likely(xdp_res & (IXGBE_XDP_TX | IXGBE_XDP_REDIR))) {
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
index b8dd74453655..1b7132fa70de 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
@@ -270,7 +270,7 @@ struct sk_buff *mlx5e_xsk_skb_from_cqe_mpwrq_linear(struct mlx5e_rq *rq,
 	/* mxbuf->rq is set on allocation, but cqe is per-packet so set it here */
 	mxbuf->cqe = cqe;
 	xsk_buff_set_size(&mxbuf->xdp, cqe_bcnt);
-	xsk_buff_dma_sync_for_cpu(&mxbuf->xdp, rq->xsk_pool);
+	xsk_buff_dma_sync_for_cpu(&mxbuf->xdp);
 	net_prefetch(mxbuf->xdp.data);
 
 	/* Possible flows:
@@ -319,7 +319,7 @@ struct sk_buff *mlx5e_xsk_skb_from_cqe_linear(struct mlx5e_rq *rq,
 	/* mxbuf->rq is set on allocation, but cqe is per-packet so set it here */
 	mxbuf->cqe = cqe;
 	xsk_buff_set_size(&mxbuf->xdp, cqe_bcnt);
-	xsk_buff_dma_sync_for_cpu(&mxbuf->xdp, rq->xsk_pool);
+	xsk_buff_dma_sync_for_cpu(&mxbuf->xdp);
 	net_prefetch(mxbuf->xdp.data);
 
 	prog = rcu_dereference(rq->xdp_prog);
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index d601b5faaed5..5e5d9fd0bfd5 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -917,7 +917,7 @@ INDIRECT_CALLABLE_SCOPE bool mlx5e_post_rx_wqes(struct mlx5e_rq *rq)
 
 	if (!rq->xsk_pool) {
 		count = mlx5e_refill_rx_wqes(rq, head, wqe_bulk);
-	} else if (likely(!rq->xsk_pool->dma_need_sync)) {
+	} else if (likely(dma_skip_sync(rq->pdev))) {
 		mlx5e_xsk_free_rx_wqes(rq, head, wqe_bulk);
 		count = mlx5e_xsk_alloc_rx_wqes_batched(rq, head, wqe_bulk);
 	} else {
diff --git a/drivers/net/ethernet/netronome/nfp/nfd3/xsk.c b/drivers/net/ethernet/netronome/nfp/nfd3/xsk.c
index 45be6954d5aa..01cfa9cc1b5e 100644
--- a/drivers/net/ethernet/netronome/nfp/nfd3/xsk.c
+++ b/drivers/net/ethernet/netronome/nfp/nfd3/xsk.c
@@ -184,7 +184,7 @@ nfp_nfd3_xsk_rx(struct nfp_net_rx_ring *rx_ring, int budget,
 		xrxbuf->xdp->data += meta_len;
 		xrxbuf->xdp->data_end = xrxbuf->xdp->data + pkt_len;
 		xdp_set_data_meta_invalid(xrxbuf->xdp);
-		xsk_buff_dma_sync_for_cpu(xrxbuf->xdp, r_vec->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(xrxbuf->xdp);
 		net_prefetch(xrxbuf->xdp->data);
 
 		if (meta_len) {
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index ae2ffa9595d6..d988f5ac8166 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5364,7 +5364,7 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 
 		/* RX buffer is good and fit into a XSK pool buffer */
 		buf->xdp->data_end = buf->xdp->data + buf1_len;
-		xsk_buff_dma_sync_for_cpu(buf->xdp, rx_q->xsk_pool);
+		xsk_buff_dma_sync_for_cpu(buf->xdp);
 
 		prog = READ_ONCE(priv->xdp_prog);
 		res = __stmmac_xdp_run_prog(priv, prog, buf->xdp);
diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index ce60ecd48a4d..ecea2a329b1d 100644
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -338,7 +338,6 @@ static struct xsk_dma_map *xp_create_dma_map(struct device *dev, struct net_devi
 
 	dma_map->netdev = netdev;
 	dma_map->dev = dev;
-	dma_map->dma_need_sync = false;
 	dma_map->dma_pages_cnt = nr_pages;
 	refcount_set(&dma_map->users, 1);
 	list_add(&dma_map->list, &umem->xsk_dma_list);
@@ -424,7 +423,6 @@ static int xp_init_dma_info(struct xsk_buff_pool *pool, struct xsk_dma_map *dma_
 
 	pool->dev = dma_map->dev;
 	pool->dma_pages_cnt = dma_map->dma_pages_cnt;
-	pool->dma_need_sync = dma_map->dma_need_sync;
 	memcpy(pool->dma_pages, dma_map->dma_pages,
 	       pool->dma_pages_cnt * sizeof(*pool->dma_pages));
 
@@ -460,8 +458,6 @@ int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
 			__xp_dma_unmap(dma_map, attrs);
 			return -ENOMEM;
 		}
-		if (dma_need_sync(dev, dma))
-			dma_map->dma_need_sync = true;
 		dma_map->dma_pages[i] = dma;
 	}
 
@@ -557,11 +553,9 @@ struct xdp_buff *xp_alloc(struct xsk_buff_pool *pool)
 	xskb->xdp.data_meta = xskb->xdp.data;
 	xskb->xdp.flags = 0;
 
-	if (pool->dma_need_sync) {
-		dma_sync_single_range_for_device(pool->dev, xskb->dma, 0,
-						 pool->frame_len,
-						 DMA_BIDIRECTIONAL);
-	}
+	dma_sync_single_for_device(pool->dev, xskb->dma, pool->frame_len,
+				   DMA_BIDIRECTIONAL);
+
 	return &xskb->xdp;
 }
 EXPORT_SYMBOL(xp_alloc);
@@ -633,7 +627,7 @@ u32 xp_alloc_batch(struct xsk_buff_pool *pool, struct xdp_buff **xdp, u32 max)
 {
 	u32 nb_entries1 = 0, nb_entries2;
 
-	if (unlikely(pool->dma_need_sync)) {
+	if (unlikely(!dma_skip_sync(pool->dev))) {
 		struct xdp_buff *buff;
 
 		/* Slow path */
@@ -693,18 +687,3 @@ dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr)
 		(addr & ~PAGE_MASK);
 }
 EXPORT_SYMBOL(xp_raw_get_dma);
-
-void xp_dma_sync_for_cpu_slow(struct xdp_buff_xsk *xskb)
-{
-	dma_sync_single_range_for_cpu(xskb->pool->dev, xskb->dma, 0,
-				      xskb->pool->frame_len, DMA_BIDIRECTIONAL);
-}
-EXPORT_SYMBOL(xp_dma_sync_for_cpu_slow);
-
-void xp_dma_sync_for_device_slow(struct xsk_buff_pool *pool, dma_addr_t dma,
-				 size_t size)
-{
-	dma_sync_single_range_for_device(pool->dev, dma, 0,
-					 size, DMA_BIDIRECTIONAL);
-}
-EXPORT_SYMBOL(xp_dma_sync_for_device_slow);
-- 
2.43.0

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Robin Murphy]

On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> Some platforms do have DMA, but DMA there is always direct and coherent.
> Currently, even on such platforms DMA sync operations are compiled and
> called.
> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
> either sync operations are needed or there is DMA ops or swiotlb
> enabled. Set dma_need_sync() and dma_skip_sync() depending on this
> symbol state and don't call sync ops when dma_skip_sync() is true.
> The change allows for future optimizations of DMA sync calls depending
> on compile-time or runtime conditions.
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> ---
>   kernel/dma/Kconfig          |  4 ++
>   include/linux/dma-mapping.h | 80 +++++++++++++++++++++++++++++++------
>   kernel/dma/mapping.c        | 20 +++++-----
>   3 files changed, 81 insertions(+), 23 deletions(-)
> 
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index d62f5957f36b..1c9ff05b1ecb 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -107,6 +107,10 @@ config DMA_BOUNCE_UNALIGNED_KMALLOC
>   	bool
>   	depends on SWIOTLB
>   
> +config DMA_NEED_SYNC
> +	def_bool ARCH_HAS_SYNC_DMA_FOR_DEVICE || ARCH_HAS_SYNC_DMA_FOR_CPU || \
> +		 ARCH_HAS_SYNC_DMA_FOR_CPU_ALL || DMA_OPS || SWIOTLB

I'm not sure DMA_OPS belongs here - several architectures have 
non-trivial ops without syncs, e.g. Alpha.

> +
>   config DMA_RESTRICTED_POOL
>   	bool "DMA Restricted Pool"
>   	depends on OF && OF_RESERVED_MEM && SWIOTLB
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 4a658de44ee9..6c7640441214 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -117,13 +117,13 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
>   		size_t size, enum dma_data_direction dir, unsigned long attrs);
>   void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
>   		enum dma_data_direction dir, unsigned long attrs);
> -void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
> +void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
>   		enum dma_data_direction dir);
> -void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
> +void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
>   		size_t size, enum dma_data_direction dir);
> -void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
> +void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
>   		    int nelems, enum dma_data_direction dir);
> -void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
> +void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
>   		       int nelems, enum dma_data_direction dir);
>   void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
>   		gfp_t flag, unsigned long attrs);
> @@ -147,7 +147,7 @@ u64 dma_get_required_mask(struct device *dev);
>   bool dma_addressing_limited(struct device *dev);
>   size_t dma_max_mapping_size(struct device *dev);
>   size_t dma_opt_mapping_size(struct device *dev);
> -bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
> +bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr);
>   unsigned long dma_get_merge_boundary(struct device *dev);
>   struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
>   		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs);
> @@ -195,19 +195,19 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
>   		size_t size, enum dma_data_direction dir, unsigned long attrs)
>   {
>   }
> -static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
> -		size_t size, enum dma_data_direction dir)
> +static inline void __dma_sync_single_for_cpu(struct device *dev,
> +		dma_addr_t addr, size_t size, enum dma_data_direction dir)

To me it would feel more logical to put all the wrappers inside the 
#ifdef CONFIG_HAS_DMA and not touch these stubs at all (what does it 
mean to skip an inline no-op?). Or in fact, if dma_skip_sync() is 
constant false for !HAS_DMA, then we could also just make the external 
function declarations unconditional and remove the stubs. Not a critical 
matter though, and I defer to whatever Christoph thinks is most 
maintainable.

>   {
>   }
> -static inline void dma_sync_single_for_device(struct device *dev,
> +static inline void __dma_sync_single_for_device(struct device *dev,
>   		dma_addr_t addr, size_t size, enum dma_data_direction dir)
>   {
>   }
> -static inline void dma_sync_sg_for_cpu(struct device *dev,
> +static inline void __dma_sync_sg_for_cpu(struct device *dev,
>   		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
>   {
>   }
> -static inline void dma_sync_sg_for_device(struct device *dev,
> +static inline void __dma_sync_sg_for_device(struct device *dev,
>   		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
>   {
>   }
> @@ -277,7 +277,7 @@ static inline size_t dma_opt_mapping_size(struct device *dev)
>   {
>   	return 0;
>   }
> -static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
> +static inline bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
>   {
>   	return false;
>   }
> @@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
>   	return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
>   }
>   
> +static inline void __dma_sync_single_range_for_cpu(struct device *dev,
> +		dma_addr_t addr, unsigned long offset, size_t size,
> +		enum dma_data_direction dir)
> +{
> +	__dma_sync_single_for_cpu(dev, addr + offset, size, dir);
> +}
> +
> +static inline void __dma_sync_single_range_for_device(struct device *dev,
> +		dma_addr_t addr, unsigned long offset, size_t size,
> +		enum dma_data_direction dir)
> +{
> +	__dma_sync_single_for_device(dev, addr + offset, size, dir);
> +}

There is no need to introduce these two.

> +
> +static inline bool dma_skip_sync(const struct device *dev)
> +{
> +	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
> +}
> +
> +static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
> +{
> +	return !dma_skip_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
> +}

That's a bit of a mind-bender... is it actually just

	return !dma_skip_sync(dev) && __dma_need_sync(dev, dma_addr);

?

(I do still think the negative flag makes it all a little harder to 
follow in general than a positive "device needs to consider syncs" flag 
would.)

> +static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
> +		size_t size, enum dma_data_direction dir)
> +{
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_single_for_cpu(dev, addr, size, dir);
> +}
> +
> +static inline void dma_sync_single_for_device(struct device *dev,
> +		dma_addr_t addr, size_t size, enum dma_data_direction dir)
> +{
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_single_for_device(dev, addr, size, dir);
> +}
> +
> +static inline void dma_sync_sg_for_cpu(struct device *dev,
> +		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
> +{
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_sg_for_cpu(dev, sg, nelems, dir);
> +}
> +
> +static inline void dma_sync_sg_for_device(struct device *dev,
> +		struct scatterlist *sg, int nelems, enum dma_data_direction dir)
> +{
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_sg_for_device(dev, sg, nelems, dir);
> +}
> +
>   static inline void dma_sync_single_range_for_cpu(struct device *dev,
>   		dma_addr_t addr, unsigned long offset, size_t size,
>   		enum dma_data_direction dir)
>   {
> -	return dma_sync_single_for_cpu(dev, addr + offset, size, dir);
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_single_for_cpu(dev, addr + offset, size, dir);
>   }
>   
>   static inline void dma_sync_single_range_for_device(struct device *dev,
>   		dma_addr_t addr, unsigned long offset, size_t size,
>   		enum dma_data_direction dir)
>   {
> -	return dma_sync_single_for_device(dev, addr + offset, size, dir);
> +	if (!dma_skip_sync(dev))
> +		__dma_sync_single_for_device(dev, addr + offset, size, dir);
>   }

These two don't need changing either, since the dma_sync_single_* 
wrappers have already taken care of it.

Thanks,
Robin.

Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Robin Murphy]

On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> Quite often, devices do not need dma_sync operations on x86_64 at least.
> Indeed, when dev_is_dma_coherent(dev) is true and
> dev_use_swiotlb(dev) is false, iommu_dma_sync_single_for_cpu()
> and friends do nothing.
> 
> However, indirectly calling them when CONFIG_RETPOLINE=y consumes about
> 10% of cycles on a cpu receiving packets from softirq at ~100Gbit rate.
> Even if/when CONFIG_RETPOLINE is not set, there is a cost of about 3%.
> 
> Add dev->skip_dma_sync boolean which is set during the device
> initialization depending on the setup: dev_is_dma_coherent() for the
> direct DMA, !(sync_single_for_device || sync_single_for_cpu) or the new
> dma_map_ops flag, %DMA_F_CAN_SKIP_SYNC, advertised for non-NULL DMA ops.
> Then later, if/when swiotlb is used for the first time, the flag
> is turned off, from swiotlb_tbl_map_single().
> 
> On iavf, the UDP trafficgen with XDP_DROP in skb mode test shows
> +3-5% increase for direct DMA.
> 
> Suggested-by: Christoph Hellwig <hch@lst.de> # direct DMA shortcut
> Co-developed-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> ---
>   include/linux/device.h      |  5 +++++
>   include/linux/dma-map-ops.h | 21 ++++++++++++++++++++
>   include/linux/dma-mapping.h |  6 +++++-
>   drivers/base/dd.c           |  2 ++
>   kernel/dma/mapping.c        | 39 ++++++++++++++++++++++++++++++++++++-
>   kernel/dma/swiotlb.c        |  8 ++++++++
>   6 files changed, 79 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 97c4b046c09d..f23e6a32bea0 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -686,6 +686,8 @@ struct device_physical_location {
>    *		other devices probe successfully.
>    * @dma_coherent: this particular device is dma coherent, even if the
>    *		architecture supports non-coherent devices.
> + * @dma_skip_sync: DMA sync operations can be skipped for coherent non-SWIOTLB
> + *		buffers.
>    * @dma_ops_bypass: If set to %true then the dma_ops are bypassed for the
>    *		streaming DMA operations (->map_* / ->unmap_* / ->sync_*),
>    *		and optionall (if the coherent mask is large enough) also
> @@ -800,6 +802,9 @@ struct device {
>       defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
>   	bool			dma_coherent:1;
>   #endif
> +#ifdef CONFIG_DMA_NEED_SYNC
> +	bool			dma_skip_sync:1;
> +#endif
>   #ifdef CONFIG_DMA_OPS_BYPASS
>   	bool			dma_ops_bypass : 1;
>   #endif
> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> index 4abc60f04209..327b73f653ad 100644
> --- a/include/linux/dma-map-ops.h
> +++ b/include/linux/dma-map-ops.h
> @@ -18,8 +18,11 @@ struct iommu_ops;
>    *
>    * DMA_F_PCI_P2PDMA_SUPPORTED: Indicates the dma_map_ops implementation can
>    * handle PCI P2PDMA pages in the map_sg/unmap_sg operation.
> + * DMA_F_CAN_SKIP_SYNC: DMA sync operations can be skipped if the device is
> + * coherent and it's not an SWIOTLB buffer.
>    */
>   #define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
> +#define DMA_F_CAN_SKIP_SYNC		BIT(1)

Yuck, please be consistent - either match the style of the existing 
code, or change that to BIT(0) as well.

>   struct dma_map_ops {
>   	unsigned int flags;
> @@ -111,6 +114,24 @@ static inline void set_dma_ops(struct device *dev,
>   }
>   #endif /* CONFIG_DMA_OPS */
>   
> +#ifdef CONFIG_DMA_NEED_SYNC
> +void dma_setup_skip_sync(struct device *dev);
> +
> +static inline void dma_clear_skip_sync(struct device *dev)
> +{
> +	/* Clear it only once so that the function can be called on hotpath */
> +	if (unlikely(dev->dma_skip_sync))
> +		dev->dma_skip_sync = false;
> +}
> +#else /* !CONFIG_DMA_NEED_SYNC */
> +static inline void dma_setup_skip_sync(struct device *dev)
> +{
> +}
> +static inline void dma_clear_skip_sync(struct device *dev)
> +{
> +}
> +#endif /* !CONFIG_DMA_NEED_SYNC */
> +
>   #ifdef CONFIG_DMA_CMA
>   extern struct cma *dma_contiguous_default_area;
>   
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 6c7640441214..d85ae541c267 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -364,7 +364,11 @@ static inline void __dma_sync_single_range_for_device(struct device *dev,
>   
>   static inline bool dma_skip_sync(const struct device *dev)
>   {
> -	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
> +#ifdef CONFIG_DMA_NEED_SYNC
> +	return dev->dma_skip_sync;
> +#else
> +	return true;
> +#endif
>   }
>   
>   static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 85152537dbf1..67ad3e1d51f6 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -642,6 +642,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>   			goto pinctrl_bind_failed;
>   	}
>   
> +	dma_setup_skip_sync(dev);
> +
>   	ret = driver_sysfs_add(dev);
>   	if (ret) {
>   		pr_err("%s: driver_sysfs_add(%s) failed\n",
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 85feaa0e008c..5f588e31ea89 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -846,8 +846,14 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
>   	const struct dma_map_ops *ops = get_dma_ops(dev);
>   
>   	if (dma_map_direct(dev, ops))
> +		/*
> +		 * dma_skip_sync could've been set to false on first SWIOTLB
> +		 * buffer mapping, but @dma_addr is not necessary an SWIOTLB
> +		 * buffer. In this case, fall back to more granular check.
> +		 */
>   		return dma_direct_need_sync(dev, dma_addr);
> -	return ops->sync_single_for_cpu || ops->sync_single_for_device;
> +
> +	return true;
>   }
>   EXPORT_SYMBOL_GPL(__dma_need_sync);
>   
> @@ -861,3 +867,34 @@ unsigned long dma_get_merge_boundary(struct device *dev)
>   	return ops->get_merge_boundary(dev);
>   }
>   EXPORT_SYMBOL_GPL(dma_get_merge_boundary);
> +
> +#ifdef CONFIG_DMA_NEED_SYNC
> +void dma_setup_skip_sync(struct device *dev)
> +{
> +	const struct dma_map_ops *ops = get_dma_ops(dev);
> +
> +	if (dma_map_direct(dev, ops))

For DMA_OPS_BYPASS this will be making the decision based on the default 
dma_mask, but a driver could subsequently set a smaller mask for which 
the bypass condition will no longer be true.

Maybe instead of driver probe this setup should actually be tied in to 
dma_set_mask() anyway?

> +		/*
> +		 * dma_skip_sync will be set to false on first SWIOTLB buffer
> +		 * mapping, if any. During the device initialization, it's
> +		 * enough to check only for DMA coherence.
> +		 */
> +		dev->dma_skip_sync = dev_is_dma_coherent(dev);
> +	else if (!ops->sync_single_for_device && !ops->sync_single_for_cpu)

I guess this was the existing condition from dma_need_sync(), but now 
it's on a one-off slow path it might be nice to check the sync_sg_* ops 
as well for completeness, or at least comment that nobody should be 
implementing those without also implementing the sync_single_* ops.

> +		/*
> +		 * Synchronization is not possible when none of DMA sync ops
> +		 * is set. This check precedes the below one as it disables
> +		 * the synchronization unconditionally.
> +		 */
> +		dev->dma_skip_sync = true;
> +	else if (ops->flags & DMA_F_CAN_SKIP_SYNC)

Personally I'd combine this into the dma-direct condition.

> +		/*
> +		 * Assume that when ``DMA_F_CAN_SKIP_SYNC`` is advertised,
> +		 * the conditions for synchronizing are the same as with
> +		 * the direct DMA.
> +		 */
> +		dev->dma_skip_sync = dev_is_dma_coherent(dev);
> +	else
> +		dev->dma_skip_sync = false;
> +}
> +#endif /* CONFIG_DMA_NEED_SYNC */
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index b079a9a8e087..0b737eab4d48 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -1323,6 +1323,12 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
>   		return (phys_addr_t)DMA_MAPPING_ERROR;
>   	}
>   
> +	/*
> +	 * If dma_skip_sync was set, reset it to false on first SWIOTLB buffer
> +	 * mapping to always sync SWIOTLB buffers.
> +	 */
> +	dma_clear_skip_sync(dev);
> +
>   	/*
>   	 * Save away the mapping from the original address to the DMA address.
>   	 * This is needed when we sync the memory.  Then we sync the buffer if
> @@ -1640,6 +1646,8 @@ struct page *swiotlb_alloc(struct device *dev, size_t size)
>   	if (index == -1)
>   		return NULL;
>   
> +	dma_clear_skip_sync(dev);

We don't need this here, since this isn't a streaming API path.

Thanks,
Robin.

> +
>   	tlb_addr = slot_addr(pool->start, index);
>   
>   	return pfn_to_page(PFN_DOWN(tlb_addr));

Re: [PATCH net-next v3 3/7] iommu/dma: avoid expensive indirect calls for sync operations

[Robin Murphy]

On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> When IOMMU is on, the actual synchronization happens in the same cases
> as with the direct DMA. Advertise %DMA_F_CAN_SKIP_SYNC in IOMMU DMA to
> skip sync ops calls (indirect) for non-SWIOTLB buffers.
> 
> perf profile before the patch:
> 
>      18.53%  [kernel]       [k] gq_rx_skb
>      14.77%  [kernel]       [k] napi_reuse_skb
>       8.95%  [kernel]       [k] skb_release_data
>       5.42%  [kernel]       [k] dev_gro_receive
>       5.37%  [kernel]       [k] memcpy
> <*>  5.26%  [kernel]       [k] iommu_dma_sync_sg_for_cpu
>       4.78%  [kernel]       [k] tcp_gro_receive
> <*>  4.42%  [kernel]       [k] iommu_dma_sync_sg_for_device
>       4.12%  [kernel]       [k] ipv6_gro_receive
>       3.65%  [kernel]       [k] gq_pool_get
>       3.25%  [kernel]       [k] skb_gro_receive
>       2.07%  [kernel]       [k] napi_gro_frags
>       1.98%  [kernel]       [k] tcp6_gro_receive
>       1.27%  [kernel]       [k] gq_rx_prep_buffers
>       1.18%  [kernel]       [k] gq_rx_napi_handler
>       0.99%  [kernel]       [k] csum_partial
>       0.74%  [kernel]       [k] csum_ipv6_magic
>       0.72%  [kernel]       [k] free_pcp_prepare
>       0.60%  [kernel]       [k] __napi_poll
>       0.58%  [kernel]       [k] net_rx_action
>       0.56%  [kernel]       [k] read_tsc
> <*>  0.50%  [kernel]       [k] __x86_indirect_thunk_r11
>       0.45%  [kernel]       [k] memset
> 
> After patch, lines with <*> no longer show up, and overall
> cpu usage looks much better (~60% instead of ~72%):
> 
>      25.56%  [kernel]       [k] gq_rx_skb
>       9.90%  [kernel]       [k] napi_reuse_skb
>       7.39%  [kernel]       [k] dev_gro_receive
>       6.78%  [kernel]       [k] memcpy
>       6.53%  [kernel]       [k] skb_release_data
>       6.39%  [kernel]       [k] tcp_gro_receive
>       5.71%  [kernel]       [k] ipv6_gro_receive
>       4.35%  [kernel]       [k] napi_gro_frags
>       4.34%  [kernel]       [k] skb_gro_receive
>       3.50%  [kernel]       [k] gq_pool_get
>       3.08%  [kernel]       [k] gq_rx_napi_handler
>       2.35%  [kernel]       [k] tcp6_gro_receive
>       2.06%  [kernel]       [k] gq_rx_prep_buffers
>       1.32%  [kernel]       [k] csum_partial
>       0.93%  [kernel]       [k] csum_ipv6_magic
>       0.65%  [kernel]       [k] net_rx_action
> 
> iavf yields +10% of Mpps on Rx. This also unblocks batched allocations
> of XSk buffers when IOMMU is active.

Acked-by: Robin Murphy <robin.murphy@arm.com>

> Co-developed-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> ---
>   drivers/iommu/dma-iommu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 50ccc4f1ef81..4ab9ac13d362 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1707,7 +1707,8 @@ static size_t iommu_dma_opt_mapping_size(void)
>   }
>   
>   static const struct dma_map_ops iommu_dma_ops = {
> -	.flags			= DMA_F_PCI_P2PDMA_SUPPORTED,
> +	.flags			= DMA_F_PCI_P2PDMA_SUPPORTED |
> +				  DMA_F_CAN_SKIP_SYNC,
>   	.alloc			= iommu_dma_alloc,
>   	.free			= iommu_dma_free,
>   	.alloc_pages		= dma_common_alloc_pages,

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Robin Murphy]

On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
[...]
> +static inline bool dma_skip_sync(const struct device *dev)
> +{
> +	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
> +}

One more thing, could we please also make this conditional on 
!CONFIG_DMA_API_DEBUG so that that doesn't lose coverage for validating 
syncs?

Thanks,
Robin.

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Christoph Hellwig]

On Wed, Feb 14, 2024 at 05:20:50PM +0000, Robin Murphy wrote:
>>   +config DMA_NEED_SYNC
>> +	def_bool ARCH_HAS_SYNC_DMA_FOR_DEVICE || ARCH_HAS_SYNC_DMA_FOR_CPU || \
>> +		 ARCH_HAS_SYNC_DMA_FOR_CPU_ALL || DMA_OPS || SWIOTLB
>
> I'm not sure DMA_OPS belongs here - several architectures have non-trivial 
> ops without syncs, e.g. Alpha.

True, but peeking through the ops is a bit hard.  And I don't think it's
worth optimizing the dma sync performance on Alpha :)

>> +static inline void __dma_sync_single_for_cpu(struct device *dev,
>> +		dma_addr_t addr, size_t size, enum dma_data_direction dir)
>
> To me it would feel more logical to put all the wrappers inside the #ifdef 
> CONFIG_HAS_DMA and not touch these stubs at all (what does it mean to skip 
> an inline no-op?). Or in fact, if dma_skip_sync() is constant false for 
> !HAS_DMA, then we could also just make the external function declarations 
> unconditional and remove the stubs. Not a critical matter though, and I 
> defer to whatever Christoph thinks is most maintainable.

Your idea sounds reasonable to me, but I don't have a strong preference.

>> +static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
>> +{
>> +	return !dma_skip_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
>> +}
>
> That's a bit of a mind-bender... is it actually just
>
> 	return !dma_skip_sync(dev) && __dma_need_sync(dev, dma_addr);
>
> ?

That looks a lot more readable for sure.

> (I do still think the negative flag makes it all a little harder to follow 
> in general than a positive "device needs to consider syncs" flag would.)

Probably.

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Christoph Hellwig]

On Wed, Feb 14, 2024 at 06:09:08PM +0000, Robin Murphy wrote:
> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> [...]
>> +static inline bool dma_skip_sync(const struct device *dev)
>> +{
>> +	return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
>> +}
>
> One more thing, could we please also make this conditional on 
> !CONFIG_DMA_API_DEBUG so that that doesn't lose coverage for validating 
> syncs?

Agreed.

Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Christoph Hellwig]

On Wed, Feb 14, 2024 at 05:55:23PM +0000, Robin Murphy wrote:
>>   #define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
>> +#define DMA_F_CAN_SKIP_SYNC		BIT(1)
>
> Yuck, please be consistent - either match the style of the existing code, 
> or change that to BIT(0) as well.

Just don't use BIT() ever.  It doesn't save any typing and creates a
totally pointless mental indirection.

> I guess this was the existing condition from dma_need_sync(), but now it's 
> on a one-off slow path it might be nice to check the sync_sg_* ops as well 
> for completeness, or at least comment that nobody should be implementing 
> those without also implementing the sync_single_* ops.

Implementing only one and not the other doesn't make any sense.  Maybe
a debug check for that is ok, but thing will break badly if they aren't
in sync anyway.

Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Robin Murphy]

On 15/02/2024 5:08 am, Christoph Hellwig wrote:
> On Wed, Feb 14, 2024 at 05:55:23PM +0000, Robin Murphy wrote:
>>>    #define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
>>> +#define DMA_F_CAN_SKIP_SYNC		BIT(1)
>>
>> Yuck, please be consistent - either match the style of the existing code,
>> or change that to BIT(0) as well.
> 
> Just don't use BIT() ever.  It doesn't save any typing and creates a
> totally pointless mental indirection.
> 
>> I guess this was the existing condition from dma_need_sync(), but now it's
>> on a one-off slow path it might be nice to check the sync_sg_* ops as well
>> for completeness, or at least comment that nobody should be implementing
>> those without also implementing the sync_single_* ops.
> 
> Implementing only one and not the other doesn't make any sense.  Maybe
> a debug check for that is ok, but thing will break badly if they aren't
> in sync anyway.

In principle we *could* have an implementation which used bouncing 
purely to merge coherent scatterlist segments, thus didn't need to do 
anything for single mappings. I agree that it wouldn't seem like a 
particularly realistic thing to do these days, but I don't believe the 
API rules it out, so it might be nice to enforce that assumption 
somewhere if we are actually relying on it (although I also concur that 
this may not necessarily be the ideal place to do that in general).

Thanks,
Robin.

Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Alexander Lobakin]

From: Robin Murphy <robin.murphy@arm.com>
Date: Wed, 14 Feb 2024 17:55:23 +0000

> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:

[...]

>> +        /*
>> +         * Synchronization is not possible when none of DMA sync ops
>> +         * is set. This check precedes the below one as it disables
>> +         * the synchronization unconditionally.
>> +         */
>> +        dev->dma_skip_sync = true;
>> +    else if (ops->flags & DMA_F_CAN_SKIP_SYNC)
> 
> Personally I'd combine this into the dma-direct condition.

Please read the code comment a couple lines above :D

> 
>> +        /*
>> +         * Assume that when ``DMA_F_CAN_SKIP_SYNC`` is advertised,
>> +         * the conditions for synchronizing are the same as with
>> +         * the direct DMA.
>> +         */
>> +        dev->dma_skip_sync = dev_is_dma_coherent(dev);
>> +    else
>> +        dev->dma_skip_sync = false;
>> +}
>> +#endif /* CONFIG_DMA_NEED_SYNC */

[...]

Thanks,
Olek

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Alexander Lobakin]

From: Robin Murphy <robin.murphy@arm.com>
Date: Wed, 14 Feb 2024 17:20:50 +0000

> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:

[...]

>> -static inline void dma_sync_single_for_cpu(struct device *dev,
>> dma_addr_t addr,
>> -        size_t size, enum dma_data_direction dir)
>> +static inline void __dma_sync_single_for_cpu(struct device *dev,
>> +        dma_addr_t addr, size_t size, enum dma_data_direction dir)
> 
> To me it would feel more logical to put all the wrappers inside the
> #ifdef CONFIG_HAS_DMA and not touch these stubs at all (what does it
> mean to skip an inline no-op?). Or in fact, if dma_skip_sync() is
> constant false for !HAS_DMA, then we could also just make the external
> function declarations unconditional and remove the stubs. Not a critical
> matter though, and I defer to whatever Christoph thinks is most
> maintainable.

It's done like that due to that I'm adding a runtime check in the second
patch. I don't feel like touching this twice makes sense.

[...]

>> @@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct
>> device *dev, dma_addr_t addr,
>>       return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
>>   }
>>   +static inline void __dma_sync_single_range_for_cpu(struct device *dev,
>> +        dma_addr_t addr, unsigned long offset, size_t size,
>> +        enum dma_data_direction dir)
>> +{
>> +    __dma_sync_single_for_cpu(dev, addr + offset, size, dir);
>> +}
>> +
>> +static inline void __dma_sync_single_range_for_device(struct device
>> *dev,
>> +        dma_addr_t addr, unsigned long offset, size_t size,
>> +        enum dma_data_direction dir)
>> +{
>> +    __dma_sync_single_for_device(dev, addr + offset, size, dir);
>> +}
> 
> There is no need to introduce these two.

I already replied to this in the previous thread. Some subsys may want
to check for the shortcut earlier to avoid call ladders of their own
functions. See patch 6 for example where I use this one.

> 
>> +
>> +static inline bool dma_skip_sync(const struct device *dev)
>> +{
>> +    return !IS_ENABLED(CONFIG_DMA_NEED_SYNC);
>> +}
>> +
>> +static inline bool dma_need_sync(struct device *dev, dma_addr_t
>> dma_addr)
>> +{
>> +    return !dma_skip_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
>> +}
> 
> That's a bit of a mind-bender... is it actually just
> 
>     return !dma_skip_sync(dev) && __dma_need_sync(dev, dma_addr);

Oh, indeed ._.

> 
> ?
> 
> (I do still think the negative flag makes it all a little harder to
> follow in general than a positive "device needs to consider syncs" flag
> would.)

I think it was in the original Eric's idea and I kept this.
I'm fine with inverting it.

[...]

> Thanks,
> Robin.

Thanks,
Olek

Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

[Robin Murphy]

On 19/02/2024 12:49 pm, Alexander Lobakin wrote:
> From: Robin Murphy <robin.murphy@arm.com>
> Date: Wed, 14 Feb 2024 17:55:23 +0000
> 
>> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> 
> [...]
> 
>>> +        /*
>>> +         * Synchronization is not possible when none of DMA sync ops
>>> +         * is set. This check precedes the below one as it disables
>>> +         * the synchronization unconditionally.
>>> +         */
>>> +        dev->dma_skip_sync = true;
>>> +    else if (ops->flags & DMA_F_CAN_SKIP_SYNC)
>>
>> Personally I'd combine this into the dma-direct condition.
> 
> Please read the code comment a couple lines above :D

And my point is that that logic is not actually useful, since it would 
be nonsensical for ops to set DMA_F_CAN_SKIP_SYNC if they don't even 
implement sync ops anyway.

If the intent of DMA_F_CAN_SKIP_SYNC is to mean "behaves like 
dma-direct", then "if (dma_map_direct(...) || ops->flags & 
DMA_F_CAN_SKIP_SYNC)" is an entirely logical and expected condition.

Thanks,
Robin.

Re: [PATCH net-next v3 1/7] dma: compile-out DMA sync op calls when not used

[Robin Murphy]

On 19/02/2024 12:53 pm, Alexander Lobakin wrote:
> From: Robin Murphy <robin.murphy@arm.com>
> Date: Wed, 14 Feb 2024 17:20:50 +0000
> 
>> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> 
> [...]
> 
>>> -static inline void dma_sync_single_for_cpu(struct device *dev,
>>> dma_addr_t addr,
>>> -        size_t size, enum dma_data_direction dir)
>>> +static inline void __dma_sync_single_for_cpu(struct device *dev,
>>> +        dma_addr_t addr, size_t size, enum dma_data_direction dir)
>>
>> To me it would feel more logical to put all the wrappers inside the
>> #ifdef CONFIG_HAS_DMA and not touch these stubs at all (what does it
>> mean to skip an inline no-op?). Or in fact, if dma_skip_sync() is
>> constant false for !HAS_DMA, then we could also just make the external
>> function declarations unconditional and remove the stubs. Not a critical
>> matter though, and I defer to whatever Christoph thinks is most
>> maintainable.
> 
> It's done like that due to that I'm adding a runtime check in the second
> patch. I don't feel like touching this twice makes sense.

Huh? Why would anything need touching twice? All I'm saying is that it's 
pretty pointless to add any invocations of dma_skip_sync() in !HAS_DMA 
paths where we already know the whole API is stubbed out anyway. The 
only cases which are worth differentiating here are HAS_DMA + 
DMA_NEED_SYNC vs. HAS_DMA + !DMA_NEED_SYNC (with the subsequent runtime 
check then just subdividing the former).

> 
> [...]
> 
>>> @@ -348,18 +348,72 @@ static inline void dma_unmap_single_attrs(struct
>>> device *dev, dma_addr_t addr,
>>>        return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
>>>    }
>>>    +static inline void __dma_sync_single_range_for_cpu(struct device *dev,
>>> +        dma_addr_t addr, unsigned long offset, size_t size,
>>> +        enum dma_data_direction dir)
>>> +{
>>> +    __dma_sync_single_for_cpu(dev, addr + offset, size, dir);
>>> +}
>>> +
>>> +static inline void __dma_sync_single_range_for_device(struct device
>>> *dev,
>>> +        dma_addr_t addr, unsigned long offset, size_t size,
>>> +        enum dma_data_direction dir)
>>> +{
>>> +    __dma_sync_single_for_device(dev, addr + offset, size, dir);
>>> +}
>>
>> There is no need to introduce these two.
> 
> I already replied to this in the previous thread. Some subsys may want
> to check for the shortcut earlier to avoid call ladders of their own
> functions. See patch 6 for example where I use this one.

Ugh, no. If the page pool code wants to be clever poking around and 
sidestepping parts of the documented API, it can flippin' well open-code 
a single addition to call __dma_sync_single_for_device() directly 
itself. I'm not at all keen on having to maintain "common" APIs for such 
niche trickery.

Thanks,
Robin.