Chao Gao 136a9b3766 dma-direct: avoid redundant memory sync for swiotlb ... commit 9e02977bfa upstream. 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%. Fixes: 55897af630 ("dma-direct: merge swiotlb_dma_ops into the dma_direct code") 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> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2022-04-20 09:36:27 +02:00
..
coherent.c	dma-mapping: use 'bitmap_zalloc()' when applicable	2021-10-27 08:20:09 +02:00
contiguous.c
debug.c	dma-debug: fix return value of __setup handlers	2022-04-08 13:58:26 +02:00
debug.h	dma-debug: teach add_dma_entry() about DMA_ATTR_SKIP_CPU_SYNC	2021-10-18 12:46:45 +02:00
direct.c	dma-direct: add a dma_direct_use_pool helper	2021-12-08 16:46:35 +01:00
direct.h	dma-direct: avoid redundant memory sync for swiotlb	2022-04-20 09:36:27 +02:00
dummy.c	dma-mapping: return error code from dma_dummy_map_sg()	2021-08-09 17:13:06 +02:00
Kconfig	Merge branch 'stable/for-linus-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb	2021-09-03 10:34:44 -07:00
Makefile
map_benchmark.c	dma-mapping: benchmark: Add support for multi-pages map/unmap	2021-04-02 16:41:08 +02:00
mapping.c	arm64 updates for 5.16	2021-11-01 16:33:53 -07:00
ops_helpers.c	dma-mapping: handle vmalloc addresses in dma_common_{mmap,get_sgtable}	2021-07-16 11:30:26 +02:00
pool.c	dma/pool: create dma atomic pool only if dma zone has managed pages	2022-01-15 16:30:29 +02:00
remap.c	kernel/dma: remove unnecessary unmap_kernel_range	2021-04-30 11:20:40 -07:00
swiotlb.c	Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""	2022-04-08 13:58:59 +02:00