On Mon, Oct 15, 2012 at 10:19 AM, Alexander Duyck <alexander.h.du...@intel.com> wrote: > While working on 10Gb/s routing performance I found a significant amount of > time was being spent in the swiotlb DMA handler. Further digging found that a > significant amount of this was due to virtual to physical address translation > and calling the function that did it. It accounted for nearly 60% of the > total swiotlb overhead. > > This patch set works to resolve that by replacing the io_tlb_start and > io_tlb_end virtual addresses with a physical addresses. In addition it changes > the io_tlb_overflow_buffer from a virtual to a physical address. I followed > through with the cleanup to the point that the only functions that really > require the virtual address for the DMA buffer are the init, free, and > bounce functions. > > In the case of devices that are using the bounce buffers these patches should > result in only a slight performance gain if any. This is due to the locking > overhead required to map and unmap the buffers. > > In the case of devices that are not making use of bounce buffers these patches > can significantly reduce their overhead. In the case of an ixgbe routing test > for example, these changes result in 7 fewer calls to __phys_addr and > allow is_swiotlb_buffer to become inlined due to a reduction in the number of > instructions. When running a routing throughput test using small packets I > saw roughly a 6% increase in packets rates after applying these patches. This > appears to match up with the CPU overhead reduction I was tracking via perf. > > Before: > Results 10.0Mpps > > After: > Results 10.6Mpps > > Finally, I updated the parameter names for several of the core function calls > as there was some ambiguity in naming. Specifically virtual address pointers > were named dma_addr. When I changed these pointers to physical I instead used > the name tlb_addr as this value represented a physical address in the > io_tlb_start region and is less likely to be confused with a bus address. > > v2: > I reviewed the changes and realized that the first patch that was dropping > io_tlb_end and calculating the value didn't actually gain me much once I had > gone through and translated the rest of the addresses to physical addresses. > As such I have updated the patch so that it instead is converting io_tlb_end > from a virtual address to a physical address. This actually helps to reduce > the overhead for is_swiotlb_buffer and swiotlb_dma_supported by several > instructions. > > v3: > After reviewing the patches I realized I was causing some namespace pollution > since a "static char *" was being replaced with "phys_addr_t" when it should > have been "static phys_addr_t". As such I have updated the first 3 patches to > correctly replace static pointers with static physical addresses. > > --- > > Alexander Duyck (7): > swiotlb: Do not export swiotlb_bounce since there are no external > consumers > swiotlb: Use physical addresses instead of virtual in > swiotlb_tbl_sync_single > swiotlb: Use physical addresses for swiotlb_tbl_unmap_single > swiotlb: Return physical addresses when calling swiotlb_tbl_map_single > swiotlb: Make io_tlb_overflow_buffer a physical address > swiotlb: Make io_tlb_start a physical address instead of a virtual one > swiotlb: Make io_tlb_end a physical address instead of a virtual one > > > drivers/xen/swiotlb-xen.c | 25 ++-- > include/linux/swiotlb.h | 20 ++- > lib/swiotlb.c | 269 > +++++++++++++++++++++++---------------------- > 3 files changed, 163 insertions(+), 151 deletions(-) >
Is there any ETA on when this patch series might be pulled into a tree? I'm just wondering if I need to rebase this patch series and resubmit it, and if so what tree I need to rebase it off of? Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
