Re: [net] 4890b686f4: netperf.Throughput_Mbps -69.4% regression

[Feng Tang]

On Mon, Jun 27, 2022 at 10:46:21AM +0200, Eric Dumazet wrote:
> On Mon, Jun 27, 2022 at 4:38 AM Feng Tang <feng.tang@xxxxxxxxx> wrote:
[snip]
> > > >
> > > > Thanks Feng. Can you check the value of memory.kmem.tcp.max_usage_in_bytes
> > > > in /sys/fs/cgroup/memory/system.slice/lkp-bootstrap.service after making
> > > > sure that the netperf test has already run?
> > >
> > > memory.kmem.tcp.max_usage_in_bytes:0
> >
> > Sorry, I made a mistake that in the original report from Oliver, it
> > was 'cgroup v2' with a 'debian-11.1' rootfs.
> >
> > When you asked about cgroup info, I tried the job on another tbox, and
> > the original 'job.yaml' didn't work, so I kept the 'netperf' test
> > parameters and started a new job which somehow run with a 'debian-10.4'
> > rootfs and acutally run with cgroup v1.
> >
> > And as you mentioned cgroup version does make a big difference, that
> > with v1, the regression is reduced to 1% ~ 5% on different generations
> > of test platforms. Eric mentioned they also got regression report,
> > but much smaller one, maybe it's due to the cgroup version?
> 
> This was using the current net-next tree.
> Used recipe was something like:
> 
> Make sure cgroup2 is mounted or mount it by mount -t cgroup2 none $MOUNT_POINT.
> Enable memory controller by echo +memory > $MOUNT_POINT/cgroup.subtree_control.
> Create a cgroup by mkdir $MOUNT_POINT/job.
> Jump into that cgroup by echo $$ > $MOUNT_POINT/job/cgroup.procs.
> 
> <Launch tests>
> 
> The regression was smaller than 1%, so considered noise compared to
> the benefits of the bug fix.
 
Yes, 1% is just around noise level for a microbenchmark.

I went check the original test data of Oliver's report, the tests was
run 6 rounds and the performance data is pretty stable (0Day's report
will show any std deviation bigger than 2%)

The test platform is a 4 sockets 72C/144T machine, and I run the
same job (nr_tasks = 25% * nr_cpus) on one CascadeLake AP (4 nodes)
and one Icelake 2 sockets platform, and saw 75% and 53% regresson on
them.

In the first email, there is a file named 'reproduce', it shows the
basic test process:

"
  use 'performane' cpufre  governor for all CPUs

  netserver -4 -D
  modprobe sctp
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  (repeat 36 times in total) 
  ...

"

Which starts 36 (25% of nr_cpus) netperf clients. And the clients number
also matters, I tried to increase the client number from 36 to 72(50%),
and the regression is changed from 69.4% to 73.7%

Thanks,
Feng

> >
> > Thanks,
> > Feng