On Wed, Apr 21, 2021 at 09:52:40AM +0800, Yunsheng Lin wrote: > On 2021/4/21 4:34, Michal Kubecek wrote: > > However, I noticed something disturbing in the results of a simple > > 1-thread TCP_STREAM test (client sends data through a TCP connection to > > server using long writes, we measure the amount of data received by the > > server): > > > > server: 172.17.1.1, port 12543 > > iterations: 20, threads: 1, test length: 30 > > test: TCP_STREAM, message size: 1048576 > > > > 1 927403548.4 B/s, avg 927403548.4 B/s, mdev 0.0 B/s ( 0.0%) > > 2 1176317172.1 B/s, avg 1051860360.2 B/s, mdev 124456811.8 B/s ( 11.8%), confid. +/- 1581348251.3 B/s (150.3%) > > 3 927335837.8 B/s, avg 1010352186.1 B/s, mdev 117354970.3 B/s ( 11.6%), confid. +/- 357073677.2 B/s ( 35.3%) > > 4 1176728045.1 B/s, avg 1051946150.8 B/s, mdev 124576544.7 B/s ( 11.8%), confid. +/- 228863127.8 B/s ( 21.8%) > > 5 1176788216.3 B/s, avg 1076914563.9 B/s, mdev 122102985.3 B/s ( 11.3%), confid. +/- 169478943.5 B/s ( 15.7%) > > 6 1158167055.1 B/s, avg 1090456645.8 B/s, mdev 115504209.5 B/s ( 10.6%), confid. +/- 132805140.8 B/s ( 12.2%) > > 7 1176243474.4 B/s, avg 1102711907.0 B/s, mdev 111069717.1 B/s ( 10.1%), confid. +/- 110956822.2 B/s ( 10.1%) > > 8 1176771142.8 B/s, avg 1111969311.5 B/s, mdev 106744173.5 B/s ( 9.6%), confid. +/- 95417120.0 B/s ( 8.6%) > > 9 1176206364.6 B/s, avg 1119106761.8 B/s, mdev 102644185.2 B/s ( 9.2%), confid. +/- 83685200.5 B/s ( 7.5%) > > 10 1175888409.4 B/s, avg 1124784926.6 B/s, mdev 98855550.5 B/s ( 8.8%), confid. +/- 74537085.1 B/s ( 6.6%) > > 11 1176541407.6 B/s, avg 1129490061.2 B/s, mdev 95422224.8 B/s ( 8.4%), confid. +/- 67230249.7 B/s ( 6.0%) > > 12 934185352.8 B/s, avg 1113214668.9 B/s, mdev 106114984.5 B/s ( 9.5%), confid. +/- 70420712.5 B/s ( 6.3%) > > 13 1176550558.1 B/s, avg 1118086660.3 B/s, mdev 103339448.9 B/s ( 9.2%), confid. +/- 65002902.4 B/s ( 5.8%) > > 14 1176521808.8 B/s, avg 1122260599.5 B/s, mdev 100711151.3 B/s ( 9.0%), confid. +/- 60333655.0 B/s ( 5.4%) > > 15 1176744840.8 B/s, avg 1125892882.3 B/s, mdev 98240838.2 B/s ( 8.7%), confid. +/- 56319052.3 B/s ( 5.0%) > > 16 1176593778.5 B/s, avg 1129061688.3 B/s, mdev 95909740.8 B/s ( 8.5%), confid. +/- 52771633.5 B/s ( 4.7%) > > 17 1176583967.4 B/s, avg 1131857116.5 B/s, mdev 93715582.2 B/s ( 8.3%), confid. +/- 49669258.6 B/s ( 4.4%) > > 18 1176853301.8 B/s, avg 1134356904.5 B/s, mdev 91656530.2 B/s ( 8.1%), confid. +/- 46905244.8 B/s ( 4.1%) > > 19 1176592845.7 B/s, avg 1136579848.8 B/s, mdev 89709043.8 B/s ( 7.9%), confid. +/- 44424855.9 B/s ( 3.9%) > > 20 1176608117.3 B/s, avg 1138581262.2 B/s, mdev 87871692.6 B/s ( 7.7%), confid. +/- 42193098.5 B/s ( 3.7%) > > all avg 1138581262.2 B/s, mdev 87871692.6 B/s ( 7.7%), confid. +/- 42193098.5 B/s ( 3.7%) > > > > Each line shows result of one 30 second long test and average, mean > > deviation and 99% confidence interval half width through the iterations > > so far. While 17 iteration results are essentially the wire speed minus > > TCP overhead, iterations 1, 3 and 12 are more than 20% lower. As results > > of the same test on unpatched 5.12-rc7 are much more consistent (the > > lowest iteration result through the whole test was 1175939718.3 and the > > mean deviation only 276889.1 B/s), it doesn't seeem to be just a random > > fluctuation. > > I think I need to relearn the statistial math to understand the above > "99% confidence interval half width ":) An easy way to understand it is that if the last column shows 42 MB/s, it means that with 99% confidence (probability), the measured average is within 42 MB/s off the actual one. > But the problem do not seems related too much with "99% confidence > interval half width ", but with "mean deviation"? Mean deviation is a symptom here. What worries me is that most results show the same value (corresponding to fully saturated line) with very little variation, in some iterations (1, 3 and 12 here) we can suddenly see much lower value (by ~2.5 GB/s, i.e. 20-25%). And as each iteration runs the connection for 30 seconds, it cannot be just some short glitch. I managed to get tcpdump captures yesterday but they are huge even with "-s 128" (client ~5.6 GB, server ~9.0 GB) so that working with them is rather slow so I did not find anything interesting yet. > I tried using netperf, which seems only show throughput of 9415.06 > (10^6bits/sec) using 10G netdev. which tool did you used to show the > above number? 9415.06 * 10^6 b/s is 1176.9 * 10^6 B/s so it's about the same as the numbers above (the good ones, that is). As this was part of a longer test trying different thread counts from 1 to 128, I was using another utility I started writing recently: https://github.com/mkubecek/nperf It is still raw and a lot of features are missing but it can be already used for multithreaded TCP_STREAM and TCP_RR tests. In particular, the output above was with nperf -H 172.17.1.1 -l 30 -i 20 --exact -t TCP_STREAM -M 1 The results are with 1 thread so that they should be also reproducible with netperf too. But it needs to be repeated enough times, when I wanted to get the packet captures, I did 40 iterations and only two of them showed lower result. Michal
