From: Michal Kubecek <mkubecek@suse.cz>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: davem@davemloft.net, kuba@kernel.org, olteanv@gmail.com,
ast@kernel.org, daniel@iogearbox.net, andriin@fb.com,
edumazet@google.com, weiwan@google.com, cong.wang@bytedance.com,
ap420073@gmail.com, netdev@vger.kernel.org,
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mkl@pengutronix.de, linux-can@vger.kernel.org, jhs@mojatatu.com,
xiyou.wangcong@gmail.com, jiri@resnulli.us, andrii@kernel.org,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
john.fastabend@gmail.com, kpsingh@kernel.org,
bpf@vger.kernel.org, pabeni@redhat.com, mzhivich@akamai.com,
johunt@akamai.com, albcamus@gmail.com, kehuan.feng@gmail.com,
a.fatoum@pengutronix.de, atenart@kernel.org,
alexander.duyck@gmail.com, hdanton@sina.com, jgross@suse.com,
JKosina@suse.com
Subject: Re: [PATCH net v4 1/2] net: sched: fix packet stuck problem for lockless qdisc
Date: Wed, 21 Apr 2021 07:31:23 +0200 [thread overview]
Message-ID: <20210421053123.wdq3kwlvf72kwtch@lion.mk-sys.cz> (raw)
In-Reply-To: <80d64438-e3e5-e861-4da0-f6c89e3c73f7@huawei.com>
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
next prev parent reply other threads:[~2021-04-21 5:31 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 1:16 [PATCH net v4 0/2] fix packet stuck problem for lockless qdisc Yunsheng Lin
2021-04-16 1:16 ` [PATCH net v4 1/2] net: sched: " Yunsheng Lin
2021-04-19 15:29 ` Michal Kubecek
2021-04-19 23:55 ` Michal Kubecek
2021-04-20 2:23 ` Yunsheng Lin
2021-04-20 20:34 ` Michal Kubecek
2021-04-21 1:52 ` Yunsheng Lin
2021-04-21 5:31 ` Michal Kubecek [this message]
2021-04-21 8:21 ` Yunsheng Lin
2021-04-21 8:44 ` Michal Kubecek
2021-04-21 9:25 ` Yunsheng Lin
2021-04-23 9:42 ` Yunsheng Lin
2021-04-30 3:11 ` Yunsheng Lin
2021-04-30 3:15 ` Yunsheng Lin
2021-04-30 6:28 ` Michal Kubecek
2021-04-16 1:16 ` [PATCH net v4 2/2] net: sched: fix endless tx action reschedule during deactivation Yunsheng Lin
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