Re: [PATCH 08/10] swiotlb: don't dip into swiotlb pool for coherent allocations

Konrad Rzeszutek Wilk
2018-10-19T00:41:42Z

On Mon, Oct 08, 2018 at 10:02:44AM +0200, Christoph Hellwig wrote:
> All architectures that support swiotlb also have a zone that backs up
> these less than full addressing allocations (usually ZONE_DMA32).
>
> Because of that it is rather pointless to fall back to the global swiotlb
> buffer if the normal dma direct allocation failed - the only thing this
> will do is to eat up bounce buffers that would be more useful to serve
> streaming mappings.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Thank you!
> ---
> arch/arm64/mm/dma-mapping.c | 6 +--
> include/linux/swiotlb.h | 5 --
> kernel/dma/swiotlb.c | 105 +-----------------------------------
> 3 files changed, 5 insertions(+), 111 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 8d91b927e09e..eee6cfcfde9e 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -112,7 +112,7 @@ static void *__dma_alloc(struct device *dev, size_t size,
> return addr;
> }
>
> - ptr = swiotlb_alloc(dev, size, dma_handle, flags, attrs);
> + ptr = dma_direct_alloc_pages(dev, size, dma_handle, flags, attrs);
> if (!ptr)
> goto no_mem;
>
> @@ -133,7 +133,7 @@ static void *__dma_alloc(struct device *dev, size_t size,
> return coherent_ptr;
>
> no_map:
> - swiotlb_free(dev, size, ptr, *dma_handle, attrs);
> + dma_direct_free_pages(dev, size, ptr, *dma_handle, attrs);
> no_mem:
> return NULL;
> }
> @@ -151,7 +151,7 @@ static void __dma_free(struct device *dev, size_t size,
> return;
> vunmap(vaddr);
> }
> - swiotlb_free(dev, size, swiotlb_addr, dma_handle, attrs);
> + dma_direct_free_pages(dev, size, swiotlb_addr, dma_handle, attrs);
> }
>
> static dma_addr_t __swiotlb_map_page(struct device *dev, struct page *page,
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index f847c1b265c4..a387b59640a4 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -67,11 +67,6 @@ extern void swiotlb_tbl_sync_single(struct device *hwdev,
>
> /* Accessory functions. */
>
> -void *swiotlb_alloc(struct device *hwdev, size_t size, dma_addr_t *dma_handle,
> - gfp_t flags, unsigned long attrs);
> -void swiotlb_free(struct device *dev, size_t size, void *vaddr,
> - dma_addr_t dma_addr, unsigned long attrs);
> -
> extern dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
> unsigned long offset, size_t size,
> enum dma_data_direction dir,
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 4d7a4d85d71e..475a41eff3dc 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -622,78 +622,6 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
> }
> }
>
> -static inline bool dma_coherent_ok(struct device *dev, dma_addr_t addr,
> - size_t size)
> -{
> - u64 mask = DMA_BIT_MASK(32);
> -
> - if (dev && dev->coherent_dma_mask)
> - mask = dev->coherent_dma_mask;
> - return addr + size - 1 <= mask;
> -}
> -
> -static void *
> -swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
> - unsigned long attrs)
> -{
> - phys_addr_t phys_addr;
> -
> - if (swiotlb_force == SWIOTLB_NO_FORCE)
> - goto out_warn;
> -
> - phys_addr = swiotlb_tbl_map_single(dev,
> - __phys_to_dma(dev, io_tlb_start),
> - 0, size, DMA_FROM_DEVICE, attrs);
> - if (phys_addr == SWIOTLB_MAP_ERROR)
> - goto out_warn;
> -
> - *dma_handle = __phys_to_dma(dev, phys_addr);
> - if (!dma_coherent_ok(dev, *dma_handle, size))
> - goto out_unmap;
> -
> - memset(phys_to_virt(phys_addr), 0, size);
> - return phys_to_virt(phys_addr);
> -
> -out_unmap:
> - dev_warn(dev, "hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
> - (unsigned long long)dev->coherent_dma_mask,
> - (unsigned long long)*dma_handle);
> -
> - /*
> - * DMA_TO_DEVICE to avoid memcpy in unmap_single.
> - * DMA_ATTR_SKIP_CPU_SYNC is optional.
> - */
> - swiotlb_tbl_unmap_single(dev, phys_addr, size, DMA_TO_DEVICE,
> - DMA_ATTR_SKIP_CPU_SYNC);
> -out_warn:
> - if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit()) {
> - dev_warn(dev,
> - "swiotlb: coherent allocation failed, size=%zu\n",
> - size);
> - dump_stack();
> - }
> - return NULL;
> -}
> -
> -static bool swiotlb_free_buffer(struct device *dev, size_t size,
> - dma_addr_t dma_addr)
> -{
> - phys_addr_t phys_addr = dma_to_phys(dev, dma_addr);
> -
> - WARN_ON_ONCE(irqs_disabled());
> -
> - if (!is_swiotlb_buffer(phys_addr))
> - return false;
> -
> - /*
> - * DMA_TO_DEVICE to avoid memcpy in swiotlb_tbl_unmap_single.
> - * DMA_ATTR_SKIP_CPU_SYNC is optional.
> - */
> - swiotlb_tbl_unmap_single(dev, phys_addr, size, DMA_TO_DEVICE,
> - DMA_ATTR_SKIP_CPU_SYNC);
> - return true;
> -}
> -
> static dma_addr_t swiotlb_bounce_page(struct device *dev, phys_addr_t *phys,
> size_t size, enum dma_data_direction dir, unsigned long attrs)
> {
> @@ -928,39 +856,10 @@ swiotlb_dma_supported(struct device *hwdev, u64 mask)
> return __phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
> }
>
> -void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> - gfp_t gfp, unsigned long attrs)
> -{
> - void *vaddr;
> -
> - /* temporary workaround: */
> - if (gfp & __GFP_NOWARN)
> - attrs |= DMA_ATTR_NO_WARN;
> -
> - /*
> - * Don't print a warning when the first allocation attempt fails.
> - * swiotlb_alloc_coherent() will print a warning when the DMA memory
> - * allocation ultimately failed.
> - */
> - gfp |= __GFP_NOWARN;
> -
> - vaddr = dma_direct_alloc(dev, size, dma_handle, gfp, attrs);
> - if (!vaddr)
> - vaddr = swiotlb_alloc_buffer(dev, size, dma_handle, attrs);
> - return vaddr;
> -}
> -
> -void swiotlb_free(struct device *dev, size_t size, void *vaddr,
> - dma_addr_t dma_addr, unsigned long attrs)
> -{
> - if (!swiotlb_free_buffer(dev, size, dma_addr))
> - dma_direct_free(dev, size, vaddr, dma_addr, attrs);
> -}
> -
> const struct dma_map_ops swiotlb_dma_ops = {
> .mapping_error = dma_direct_mapping_error,
> - .alloc = swiotlb_alloc,
> - .free = swiotlb_free,
> + .alloc = dma_direct_alloc,
> + .free = dma_direct_free,
> .sync_single_for_cpu = swiotlb_sync_single_for_cpu,
> .sync_single_for_device = swiotlb_sync_single_for_device,
> .sync_sg_for_cpu = swiotlb_sync_sg_for_cpu,
> --
> 2.19.0
>