From: Chao Gao <chao.gao@intel.com> To: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org Cc: Kevin Tian <kevin.tian@intel.com>, Wang Zhaoyang1 <zhaoyang1.wang@intel.com>, Gao Liang <liang.gao@intel.com>, robin.murphy@arm.com, hch@lst.de Subject: [PATCH] dma-direct: avoid redundant memory sync for swiotlb Date: Tue, 12 Apr 2022 19:38:05 +0800 [thread overview] Message-ID: <20220412113805.3210-1-chao.gao@intel.com> (raw) When we looked into FIO performance with swiotlb enabled in VM, we found swiotlb_bounce() is always called one more time than expected for each DMA read request. It turns out that the bounce buffer is copied to original DMA buffer twice after the completion of a DMA request (one is done by in dma_direct_sync_single_for_cpu(), the other by swiotlb_tbl_unmap_single()). But the content in bounce buffer actually doesn't change between the two rounds of copy. So, one round of copy is redundant. Pass DMA_ATTR_SKIP_CPU_SYNC flag to swiotlb_tbl_unmap_single() to skip the memory copy in it. This fix increases FIO 64KB sequential read throughput in a guest with swiotlb=force by 5.6%. Reported-by: Wang Zhaoyang1 <zhaoyang1.wang@intel.com> Reported-by: Gao Liang <liang.gao@intel.com> Signed-off-by: Chao Gao <chao.gao@intel.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> --- kernel/dma/direct.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index 4632b0f4f72e..8a6cd53dbe8c 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -114,6 +114,7 @@ static inline void dma_direct_unmap_page(struct device *dev, dma_addr_t addr, dma_direct_sync_single_for_cpu(dev, addr, size, dir); if (unlikely(is_swiotlb_buffer(dev, phys))) - swiotlb_tbl_unmap_single(dev, phys, size, dir, attrs); + swiotlb_tbl_unmap_single(dev, phys, size, dir, + attrs | DMA_ATTR_SKIP_CPU_SYNC); } #endif /* _KERNEL_DMA_DIRECT_H */ -- 2.25.1 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
WARNING: multiple messages have this Message-ID (diff)
From: Chao Gao <chao.gao@intel.com> To: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org Cc: robin.murphy@arm.com, m.szyprowski@samsung.com, hch@lst.de, Chao Gao <chao.gao@intel.com>, Wang Zhaoyang1 <zhaoyang1.wang@intel.com>, Gao Liang <liang.gao@intel.com>, Kevin Tian <kevin.tian@intel.com> Subject: [PATCH] dma-direct: avoid redundant memory sync for swiotlb Date: Tue, 12 Apr 2022 19:38:05 +0800 [thread overview] Message-ID: <20220412113805.3210-1-chao.gao@intel.com> (raw) When we looked into FIO performance with swiotlb enabled in VM, we found swiotlb_bounce() is always called one more time than expected for each DMA read request. It turns out that the bounce buffer is copied to original DMA buffer twice after the completion of a DMA request (one is done by in dma_direct_sync_single_for_cpu(), the other by swiotlb_tbl_unmap_single()). But the content in bounce buffer actually doesn't change between the two rounds of copy. So, one round of copy is redundant. Pass DMA_ATTR_SKIP_CPU_SYNC flag to swiotlb_tbl_unmap_single() to skip the memory copy in it. This fix increases FIO 64KB sequential read throughput in a guest with swiotlb=force by 5.6%. Reported-by: Wang Zhaoyang1 <zhaoyang1.wang@intel.com> Reported-by: Gao Liang <liang.gao@intel.com> Signed-off-by: Chao Gao <chao.gao@intel.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> --- kernel/dma/direct.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index 4632b0f4f72e..8a6cd53dbe8c 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -114,6 +114,7 @@ static inline void dma_direct_unmap_page(struct device *dev, dma_addr_t addr, dma_direct_sync_single_for_cpu(dev, addr, size, dir); if (unlikely(is_swiotlb_buffer(dev, phys))) - swiotlb_tbl_unmap_single(dev, phys, size, dir, attrs); + swiotlb_tbl_unmap_single(dev, phys, size, dir, + attrs | DMA_ATTR_SKIP_CPU_SYNC); } #endif /* _KERNEL_DMA_DIRECT_H */ -- 2.25.1
next reply other threads:[~2022-04-12 11:38 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-12 11:38 Chao Gao [this message] 2022-04-12 11:38 ` [PATCH] dma-direct: avoid redundant memory sync for swiotlb Chao Gao 2022-04-12 13:21 ` Chao Gao 2022-04-12 13:21 ` Chao Gao 2022-04-12 13:33 ` Robin Murphy 2022-04-12 13:33 ` Robin Murphy 2022-04-13 1:02 ` Chao Gao 2022-04-13 1:02 ` Chao Gao 2022-04-13 4:59 ` Christoph Hellwig 2022-04-13 4:59 ` Christoph Hellwig 2022-04-13 5:46 ` Chao Gao 2022-04-13 5:46 ` Chao Gao 2022-04-13 5:49 ` Christoph Hellwig 2022-04-13 5:49 ` Christoph Hellwig 2022-04-13 13:10 ` Robin Murphy 2022-04-13 13:10 ` Robin Murphy 2022-04-13 16:44 ` Christoph Hellwig 2022-04-13 16:44 ` Christoph Hellwig
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