user/sven/linux.git/kernel/dma/direct.h, branch v5.10.221Linux Kernel
https://git.stealer.net/cgit.cgi/user/sven/linux.git/atom?h=v5.10.2212022-04-20T07:23:30Zdma-direct: avoid redundant memory sync for swiotlb2022-04-20T07:23:30ZChao Gaochao.gao@intel.com2022-04-13T06:32:22Zurn:sha1:26f827e095aba4141ffd684276ef54025de27574
commit 9e02977bfad006af328add9434c8bffa40e053bb 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: 55897af63091 ("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>
dma-mapping: move large parts of <linux/dma-direct.h> to kernel/dma2020-10-06T05:07:06ZChristoph Hellwighch@lst.de2020-09-22T13:34:22Zurn:sha1:19c65c3d30bb5a97170e425979d2e44ab2096c7d
Most of the dma_direct symbols should only be used by direct.c and
mapping.c, so move them to kernel/dma. In fact more of dma-direct.h
should eventually move, but that will require more coordination with
other subsystems.
Signed-off-by: Christoph Hellwig <hch@lst.de>