[PATCH 1/2] Break up monolithic iommu table/lock into finer graularity pools and lock

[Sowmini Varadhan <sowmini.varadhan@oracle.com>]

Investigation of multithreaded iperf experiments on an ethernet
interface show the iommu->lock as the hottest lock identified by
lockstat, with something of the order of  21M contentions out of
27M acquisitions, and an average wait time of 26 us for the lock.
This is not efficient. A more scalable design is to follow the ppc
model, where the iommu_table has multiple pools, each stretching
over a segment of the map, and with a separate lock for each pool.
This model allows for better parallelization of the iommu map search.

This patch adds the iommu range alloc/free function infrastructure.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
 include/linux/iommu-common.h |   70 +++++++++++++++
 lib/Makefile                 |    2 +-
 lib/iommu-common.c           |  200 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 271 insertions(+), 1 deletions(-)
 create mode 100644 include/linux/iommu-common.h
 create mode 100644 lib/iommu-common.c

diff --git a/include/linux/iommu-common.h b/include/linux/iommu-common.h
new file mode 100644
index 0000000..e1ae2d5
--- /dev/null
+++ b/include/linux/iommu-common.h
@@ -0,0 +1,70 @@
+#ifndef _LINUX_IOMMU_COMMON_H
+#define _LINUX_IOMMU_COMMON_H
+
+#include <asm/page.h>
+#include <linux/spinlock_types.h>
+#include <linux/device.h>
+
+#define IOMMU_NUM_CTXS  4096
+
+#define IOMMU_POOL_HASHBITS     4
+#define IOMMU_NR_POOLS          (1 << IOMMU_POOL_HASHBITS)
+#define	IOMMU_ERROR_CODE	(~(dma_addr_t)0x0)
+
+struct iommu_pool {
+	unsigned long	start;
+	unsigned long	end;
+	unsigned long	hint;
+	spinlock_t	lock;
+};
+
+struct iommu_table;
+
+struct iommu_ops {
+	void	(*demap)(void *, unsigned long, unsigned long);
+};
+
+struct iommu_table {
+	spinlock_t		table_lock;
+	void			(*flush_all)(struct iommu_table *);
+	iopte_t			*page_table;
+	u32			page_table_map_base;
+	unsigned long		iommu_control;
+	unsigned long		iommu_tsbbase;
+	unsigned long		iommu_flush;
+	unsigned long		iommu_flushinv;
+	unsigned long		iommu_tags;
+	unsigned long		iommu_ctxflush;
+	unsigned long		write_complete_reg;
+	unsigned long		dummy_page;
+	unsigned long		dummy_page_pa;
+	unsigned long		ctx_lowest_free;
+	DECLARE_BITMAP(ctx_bitmap, IOMMU_NUM_CTXS);
+	u32			dma_addr_mask;
+	u32			page_table_shift;
+	unsigned long		nr_pools;
+	const struct iommu_ops  *iommu_ops;
+	unsigned long		poolsize;
+	struct iommu_pool	arena_pool[IOMMU_NR_POOLS];
+	bool			has_large_pool;
+	struct iommu_pool	large_pool;
+	unsigned long		*map;
+};
+
+extern void iommu_tbl_pool_init(struct iommu_table *iommu,
+				unsigned long num_entries,
+				u32 page_table_shift,
+				const struct iommu_ops *iommu_ops,
+				bool large_pool);
+
+extern unsigned long iommu_tbl_range_alloc(struct device *dev,
+                                struct iommu_table *iommu,
+                                unsigned long npages,
+                                unsigned long *handle,
+                                unsigned int pool_hash);
+
+extern void iommu_tbl_range_free(struct iommu_table *iommu,
+				 dma_addr_t dma_addr, unsigned long npages,
+				 bool do_demap, void *demap_arg);
+
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 3c3b30b..0ea2ac6 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -102,7 +102,7 @@ obj-$(CONFIG_AUDIT_GENERIC) += audit.o
 obj-$(CONFIG_AUDIT_COMPAT_GENERIC) += compat_audit.o
 
 obj-$(CONFIG_SWIOTLB) += swiotlb.o
-obj-$(CONFIG_IOMMU_HELPER) += iommu-helper.o
+obj-$(CONFIG_IOMMU_HELPER) += iommu-helper.o iommu-common.o
 obj-$(CONFIG_FAULT_INJECTION) += fault-inject.o
 obj-$(CONFIG_NOTIFIER_ERROR_INJECTION) += notifier-error-inject.o
 obj-$(CONFIG_CPU_NOTIFIER_ERROR_INJECT) += cpu-notifier-error-inject.o
diff --git a/lib/iommu-common.c b/lib/iommu-common.c
new file mode 100644
index 0000000..be00461
--- /dev/null
+++ b/lib/iommu-common.c
@@ -0,0 +1,200 @@
+/*
+ * IOMMU mmap management and range allocation functions.
+ * Based almost entirely upon the powerpc iommu allocator.
+ */
+
+#include <linux/export.h>
+#include <linux/bitmap.h>
+#include <linux/bug.h>
+#include <linux/iommu-helper.h>
+#include <linux/iommu-common.h>
+#include <linux/dma-mapping.h>
+
+#define IOMMU_LARGE_ALLOC	15
+
+/*
+ * Initialize iommu_pool entries for the iommu_table. `num_entries'
+ * is the number of table entries. If `large_pool' is set to true,
+ * the top 1/4 of the table will be set aside for pool allocations
+ * of more than IOMMU_LARGE_ALLOC pages.
+ */
+extern void iommu_tbl_pool_init(struct iommu_table *iommu,
+				unsigned long num_entries,
+				u32 page_table_shift,
+				const struct iommu_ops *iommu_ops,
+				bool large_pool)
+{
+	unsigned int start, i;
+	struct iommu_pool *p = &(iommu->large_pool);
+
+	iommu->nr_pools = IOMMU_NR_POOLS;
+	iommu->page_table_shift = page_table_shift;
+	iommu->iommu_ops = iommu_ops;
+	start = 0;
+	spin_lock_init(&(iommu->table_lock));
+	iommu->has_large_pool = large_pool;
+
+	if (!large_pool)
+		iommu->poolsize = num_entries/iommu->nr_pools;
+	else
+		iommu->poolsize = (num_entries * 3 / 4)/iommu->nr_pools;
+	for (i = 0; i < iommu->nr_pools; i++) {
+		spin_lock_init(&(iommu->arena_pool[i].lock));
+		iommu->arena_pool[i].start = start;
+		iommu->arena_pool[i].hint = start;
+		start += iommu->poolsize; /* start for next pool */
+		iommu->arena_pool[i].end = start - 1;
+	}
+	if (!large_pool)
+		return;
+	/* initialize large_pool */
+	spin_lock_init(&(p->lock));
+	p->start = start;
+	p->hint = p->start;
+	p->end = num_entries;
+}
+EXPORT_SYMBOL(iommu_tbl_pool_init);
+
+unsigned long iommu_tbl_range_alloc(struct device *dev,
+				struct iommu_table *iommu,
+				unsigned long npages,
+				unsigned long *handle,
+				unsigned int pool_hash)
+{
+	unsigned long n, end, start, limit, boundary_size;
+	struct iommu_pool *arena;
+	int pass = 0;
+	unsigned int pool_nr;
+	unsigned int npools = iommu->nr_pools;
+	unsigned long flags;
+	bool largealloc = (iommu->has_large_pool && npages > IOMMU_LARGE_ALLOC);
+	unsigned long shift;
+
+	/* Sanity check */
+	if (unlikely(npages = 0)) {
+		printk_ratelimited("npages = 0\n");
+		return IOMMU_ERROR_CODE;
+	}
+
+	if (largealloc) {
+		arena = &(iommu->large_pool);
+		spin_lock_irqsave(&arena->lock, flags);
+		pool_nr = 0; /* to keep compiler happy */
+	} else {
+		/* pick out pool_nr */
+		pool_nr =  pool_hash & (npools - 1);
+		arena = &(iommu->arena_pool[pool_nr]);
+
+		/* find first available unlocked pool */
+		while (!spin_trylock_irqsave(&(arena->lock), flags)) {
+			pool_nr = (pool_nr + 1) & (iommu->nr_pools - 1);
+			arena = &(iommu->arena_pool[pool_nr]);
+		}
+	}
+
+ again:
+	if (pass = 0 && handle && *handle &&
+	    (*handle >= arena->start) && (*handle < arena->end))
+		start = *handle;
+	else
+		start = arena->hint;
+
+	limit = arena->end;
+
+	/* The case below can happen if we have a small segment appended
+	 * to a large, or when the previous alloc was at the very end of
+	 * the available space. If so, go back to the beginning and flush.
+	 */
+	if (start >= limit) {
+		start = arena->start;
+		if (iommu->flush_all)
+			iommu->flush_all(iommu);
+	}
+
+	if (dev)
+		boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
+				      1 << iommu->page_table_shift);
+	else
+		boundary_size = ALIGN(1UL << 32, 1 << iommu->page_table_shift);
+
+	shift = iommu->page_table_map_base >> iommu->page_table_shift;
+	n = iommu_area_alloc(iommu->map, limit, start, npages, shift,
+			     boundary_size >> iommu->page_table_shift, 0);
+	if (n = -1) {
+		if (likely(pass = 0)) {
+			/* First failure, rescan from the beginning.  */
+			arena->hint = arena->start;
+			if (iommu->flush_all)
+				iommu->flush_all(iommu);
+			pass++;
+			goto again;
+		} else if (!largealloc && pass <= iommu->nr_pools) {
+			spin_unlock(&(arena->lock));
+			pool_nr = (pool_nr + 1) & (iommu->nr_pools - 1);
+			arena = &(iommu->arena_pool[pool_nr]);
+			while (!spin_trylock(&(arena->lock))) {
+				pool_nr = (pool_nr + 1) & (iommu->nr_pools - 1);
+				arena = &(iommu->arena_pool[pool_nr]);
+			}
+			arena->hint = arena->start;
+			pass++;
+			goto again;
+		} else {
+			/* give up */
+			spin_unlock_irqrestore(&(arena->lock), flags);
+			return IOMMU_ERROR_CODE;
+		}
+	}
+
+	end = n + npages;
+
+	arena->hint = end;
+
+	/* Update handle for SG allocations */
+	if (handle)
+		*handle = end;
+	spin_unlock_irqrestore(&(arena->lock), flags);
+
+	return n;
+}
+EXPORT_SYMBOL(iommu_tbl_range_alloc);
+
+static struct iommu_pool *get_pool(struct iommu_table *tbl,
+				   unsigned long entry)
+{
+	struct iommu_pool *p;
+	unsigned long largepool_start = tbl->large_pool.start;
+
+	/* The large pool is the last pool at the top of the table */
+	if (tbl->has_large_pool && entry >= largepool_start) {
+		p = &tbl->large_pool;
+	} else {
+		unsigned int pool_nr = entry / tbl->poolsize;
+
+		BUG_ON(pool_nr >= tbl->nr_pools);
+		p = &tbl->arena_pool[pool_nr];
+	}
+	return p;
+}
+
+void iommu_tbl_range_free(struct iommu_table *iommu, dma_addr_t dma_addr,
+			  unsigned long npages, bool do_demap, void *demap_arg)
+{
+	unsigned long entry;
+	struct iommu_pool *pool;
+	unsigned long flags;
+	unsigned long shift = iommu->page_table_shift;
+
+	entry = (dma_addr - iommu->page_table_map_base) >> shift;
+	pool = get_pool(iommu, entry);
+
+	local_irq_save(flags);
+	if (do_demap && iommu->iommu_ops->demap != NULL)
+		(*iommu->iommu_ops->demap)(demap_arg, entry, npages);
+	local_irq_restore(flags);
+
+	spin_lock_irqsave(&(pool->lock), flags);
+	bitmap_clear(iommu->map, entry, npages);
+	spin_unlock_irqrestore(&(pool->lock), flags);
+}
+EXPORT_SYMBOL(iommu_tbl_range_free);
-- 
1.7.1