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Commit 0e4bc95d authored by Anton Blanchard's avatar Anton Blanchard Committed by Benjamin Herrenschmidt
Browse files

powerpc/iommu: Reduce spinlock coverage in iommu_alloc and iommu_free 



We currently hold the IOMMU spinlock around tce_build and tce_flush.
This causes our spinlock hold times to be much higher than required
and can impact multiqueue adapters.

This patch moves tce_build and tce_flush outside of the lock in
iommu_alloc, and tce_flush 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 32% with this patch applied.

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent c1703e85

arch/powerpc/kernel/iommu.c

+5 −10
Original line number Diff line number Diff line
@@ -170,13 +170,11 @@ static dma_addr_t iommu_alloc(struct device *dev, struct iommu_table *tbl, 
	int build_fail;



	spin_lock_irqsave(&(tbl->it_lock), flags);



	entry = iommu_range_alloc(dev, tbl, npages, NULL, mask, align_order);



	if (unlikely(entry == DMA_ERROR_CODE)) {

	spin_unlock_irqrestore(&(tbl->it_lock), flags);



	if (unlikely(entry == DMA_ERROR_CODE))

		return DMA_ERROR_CODE;

	}



	entry += tbl->it_offset;	/* Offset into real TCE table */

	ret = entry << IOMMU_PAGE_SHIFT;	/* Set the return dma address */
@@ -192,9 +190,10 @@ 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;

	}
@@ -202,8 +201,6 @@ static dma_addr_t iommu_alloc(struct device *dev, struct iommu_table *tbl, 
	if (ppc_md.tce_flush)

		ppc_md.tce_flush(tbl);



	spin_unlock_irqrestore(&(tbl->it_lock), flags);



	/* Make sure updates are seen by hardware */

	mb();
@@ -244,8 +241,8 @@ static void iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr, 
	unsigned long flags;



	spin_lock_irqsave(&(tbl->it_lock), flags);



	__iommu_free(tbl, dma_addr, npages);

	spin_unlock_irqrestore(&(tbl->it_lock), flags);



	/* 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
@@ -253,8 +250,6 @@ static void iommu_free(struct iommu_table *tbl, dma_addr_t dma_addr, 
	 */

	if (ppc_md.tce_flush)

		ppc_md.tce_flush(tbl);



	spin_unlock_irqrestore(&(tbl->it_lock), flags);

}



int iommu_map_sg(struct device *dev, struct iommu_table *tbl,