On Mon, Oct 29, 2012 at 11:18:09AM -0700, Alexander Duyck wrote: > 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?
No need to rebase it. I did a test on V2 version with Xen, but I still need to do a IA64/Calgary/AMD Vi/Intel VT-d/GART test before pushing it out. > > 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/
