Hi John, On 19 January 2015 at 02:53, <zhihong.wang at intel.com> wrote:
> This patch set optimizes memcpy for DPDK for both SSE and AVX platforms. > It also extends memcpy test coverage with unaligned cases and more test > points. > I am really interested in this work you are doing on memory copies optimized for packet data. I would like to understand it in more depth. I have a lot of questions and ideas but let me try to keep it simple for now :-) How do you benchmark? where does the "factor of 2-8" cited elsewhere in the thread come from? how can I reproduce? what results are you seeing compared with libc? I did a quick benchmark this weekend based on cachebench <http://icl.cs.utk.edu/projects/llcbench/cachebench.html>. This seems like a fairly weak benchmark (always L1 cache, always same alignment, always predictable branches). Do you think this is relevant? How does this compare with your results? I compared: rte_memcpy (the new optimized one compiled with gcc-4.9 and -march=native and -O3) memcpy from glibc 2.19 (ubuntu 14.04) memcpy from glibc 2.20 (arch linux) on hardware: E5-2620v3 (Haswell) E5-2650 (Sandy Bridge) running cachebench like this: ./cachebench -p -e1 -x1 -m14 rte_memcpy.h on Haswell: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.01 89191.88 1.00 384 0.01 96505.43 0.92 512 0.01 96509.19 1.00 768 0.01 91475.72 1.06 1024 0.01 96293.82 0.95 1536 0.01 96521.66 1.00 2048 0.01 96522.87 1.00 3072 0.01 96525.53 1.00 4096 0.01 96522.79 1.00 6144 0.01 96507.71 1.00 8192 0.01 94584.41 1.02 12288 0.01 95062.80 0.99 16384 0.01 80493.46 1.18 libc 2.20 on Haswell: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.01 65978.64 1.00 384 0.01 100249.01 0.66 512 0.01 123476.55 0.81 768 0.01 144699.86 0.85 1024 0.01 159459.88 0.91 1536 0.01 168001.92 0.95 2048 0.01 80738.31 2.08 3072 0.01 80270.02 1.01 4096 0.01 84239.84 0.95 6144 0.01 90600.13 0.93 8192 0.01 89767.94 1.01 12288 0.01 92085.98 0.97 16384 0.01 92719.95 0.99 libc 2.19 on Haswell: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.02 59871.69 1.00 384 0.01 68545.94 0.87 512 0.01 72674.23 0.94 768 0.01 79257.47 0.92 1024 0.01 79740.43 0.99 1536 0.01 85483.67 0.93 2048 0.01 87703.68 0.97 3072 0.01 86685.71 1.01 4096 0.01 87147.84 0.99 6144 0.01 68622.96 1.27 8192 0.01 70591.25 0.97 12288 0.01 72621.28 0.97 16384 0.01 67713.63 1.07 rte_memcpy on Sandy Bridge: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.02 62158.19 1.00 384 0.01 73256.41 0.85 512 0.01 82032.16 0.89 768 0.01 73919.92 1.11 1024 0.01 75937.51 0.97 1536 0.01 78280.20 0.97 2048 0.01 79562.54 0.98 3072 0.01 80800.93 0.98 4096 0.01 81453.71 0.99 6144 0.01 81915.84 0.99 8192 0.01 82427.98 0.99 12288 0.01 82789.82 1.00 16384 0.01 67519.66 1.23 libc 2.20 on Sandy Bridge: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.02 48651.20 1.00 384 0.02 57653.91 0.84 512 0.01 67909.77 0.85 768 0.01 71177.75 0.95 1024 0.01 72519.48 0.98 1536 0.01 76686.24 0.95 2048 0.19 4975.55 15.41 3072 0.19 5091.97 0.98 4096 0.19 5152.38 0.99 6144 0.18 5211.26 0.99 8192 0.18 5245.27 0.99 12288 0.18 5276.50 0.99 16384 0.18 5209.80 1.01 libc 2.19 on Sandy Bridge: Memory Copy Library Cache Test C Size Nanosec MB/sec % Chnge ------- ------- ------- ------- 256 0.02 44970.51 1.00 384 0.02 51922.46 0.87 512 0.02 57230.56 0.91 768 0.02 63438.96 0.90 1024 0.01 67506.58 0.94 1536 0.01 72579.25 0.93 2048 0.01 75722.25 0.96 3072 0.01 71039.19 1.07 4096 0.01 73946.17 0.96 6144 0.02 40969.79 1.80 8192 0.02 41396.05 0.99 12288 0.02 41830.01 0.99 16384 0.02 42032.40 1.00 Last question: Why is rte_memcpy inline? (Would making it a library function give you smaller code, comparable performance, and fast compiles?) Cheers! -Luke
