powerpc/iommu: Reduce spinlock coverage in iommu_free

This patch moves tce_free outside of the lock in iommu_free.

Some performance numbers were obtained with a Chelsio T3 adapter on
two POWER7 boxes, running a 100 session TCP round robin test.

Performance improved 25% with this patch applied.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 40 insertions, 11 deletions

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index 9c8967fa1e63..d855cfc0732d 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -190,10 +190,7 @@ static dma_addr_t iommu_alloc(struct device *dev, struct iommu_table *tbl,
          * not altered.
          */
         if (unlikely(build_fail)) {
-                spin_lock_irqsave(&(tbl->it_lock), flags);
                 __iommu_free(tbl, ret, npages);
-                spin_unlock_irqrestore(&(tbl->it_lock), flags);
-
                 return DMA_ERROR_CODE;
         }
 
@@ -207,8 +204,8 @@ static dma_addr_t iommu_alloc(struct device *dev, struct iommu_table *tbl,
         return ret;
 }
 
-static void __iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr, 
-                         unsigned int npages)
+static bool iommu_free_check(struct iommu_table *tbl, dma_addr_t dma_addr,
+                             unsigned int npages)
 {
         unsigned long entry, free_entry;
 
@@ -228,21 +225,53 @@ static void __iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr,
                         printk(KERN_INFO "\tindex     = 0x%llx\n", (u64)tbl->it_index);
                         WARN_ON(1);
                 }
-                return;
+
+                return false;
         }
 
+        return true;
+}
+
+static void __iommu_free_locked(struct iommu_table *tbl, dma_addr_t dma_addr,
+                         unsigned int npages)
+{
+        unsigned long entry, free_entry;
+
+        BUG_ON(!spin_is_locked(&tbl->it_lock));
+
+        entry = dma_addr >> IOMMU_PAGE_SHIFT;
+        free_entry = entry - tbl->it_offset;
+
+        if (!iommu_free_check(tbl, dma_addr, npages))
+                return;
+
         ppc_md.tce_free(tbl, entry, npages);
         bitmap_clear(tbl->it_map, free_entry, npages);
 }
 
-static void iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr,
-                unsigned int npages)
+static void __iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr,
+                         unsigned int npages)
 {
+        unsigned long entry, free_entry;
         unsigned long flags;
 
+        entry = dma_addr >> IOMMU_PAGE_SHIFT;
+        free_entry = entry - tbl->it_offset;
+
+        if (!iommu_free_check(tbl, dma_addr, npages))
+                return;
+
+        ppc_md.tce_free(tbl, entry, npages);
+
         spin_lock_irqsave(&(tbl->it_lock), flags);
-        __iommu_free(tbl, dma_addr, npages);
+        bitmap_clear(tbl->it_map, free_entry, npages);
         spin_unlock_irqrestore(&(tbl->it_lock), flags);
+}
+
+static void iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr,
+                unsigned int npages)
+{
+        __iommu_free(tbl, dma_addr, npages);
 
         /* Make sure TLB cache is flushed if the HW needs it. We do
          * not do an mb() here on purpose, it is not needed on any of
@@ -390,7 +419,7 @@ int iommu_map_sg(struct device *dev, struct iommu_table *tbl,
                         vaddr = s->dma_address & IOMMU_PAGE_MASK;
                         npages = iommu_num_pages(s->dma_address, s->dma_length,
                                                  IOMMU_PAGE_SIZE);
-                        __iommu_free(tbl, vaddr, npages);
+                        __iommu_free_locked(tbl, vaddr, npages);
                         s->dma_address = DMA_ERROR_CODE;
                         s->dma_length = 0;
                 }
@@ -425,7 +454,7 @@ void iommu_unmap_sg(struct iommu_table *tbl, struct scatterlist *sglist,
                         break;
                 npages = iommu_num_pages(dma_handle, sg->dma_length,
                                          IOMMU_PAGE_SIZE);
-                __iommu_free(tbl, dma_handle, npages);
+                __iommu_free_locked(tbl, dma_handle, npages);
                 sg = sg_next(sg);
         }