Hi Boris, Srinivas,
On Tue, Apr 13, 2021 at 07:28:27PM +0200, Borislav Petkov wrote:
> On Tue, Apr 13, 2021 at 09:58:01PM +0800, kernel test robot wrote:
> > Greeting,
> >
> > FYI, we noticed a -27.4% regression of stress-ng.msg.ops_per_sec due to
> > commit:
> >
> >
> > commit: 9223d0dccb8f8523754122f68316dd1a4f39f7f8 ("thermal: Move
> > therm_throt there from x86/mce")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
This seems to be another case that performance jump is caused by
kernel's data alignment change triggered by an irrelevant patch.
With a debug patch to force aligned all data sections of .o files,
the performance diff is reduced from -27.4 to -2.8%.
And from perf profile and c2c data, we did see differenc about spinlock
around calling do_msgrcv/do_msgsnd with the 2 commits
> Hmm, so I went and ran your reproducer, but simplified (see end of
> mail), on a KBL box here. The kernel is tip:x86/urgent from last week:
>
> 5.12.0-rc6+
> -----------
> stress-ng: info: [1430] dispatching hogs: 9 msg
> stress-ng: info: [1430] successful run completed in 60.01s (1 min, 0.01 secs)
> stress-ng: info: [1430] stressor bogo ops real time usr time sys
> time bogo ops/s bogo ops/s
> stress-ng: info: [1430] (secs) (secs) (secs)
> (real time) (usr+sys time)
> stress-ng: info: [1430] msg 237390147 60.01 104.03
> 255.85 3955872.56 659636.95
> stress-ng: info: [1430] for a 60.01s run time:
> stress-ng: info: [1430] 360.08s available CPU time
> stress-ng: info: [1430] 104.11s user time ( 28.91%)
> stress-ng: info: [1430] 255.93s system time ( 71.08%)
> stress-ng: info: [1430] 360.04s total time ( 99.99%)
> stress-ng: info: [1430] load average: 8.47 3.71 1.48
>
> Now the same kernel with
>
> > 4f432e8bb1 ("x86/mce: Get rid of mcheck_intel_therm_init()")
> > 9223d0dccb ("thermal: Move therm_throt there from x86/mce")
>
> reverted.
>
> 5.12.0-rc6-rev+
> ---------------
> stress-ng: info: [1246] dispatching hogs: 9 msg
> stress-ng: info: [1246] successful run completed in 60.02s (1 min, 0.02 secs)
> stress-ng: info: [1246] stressor bogo ops real time usr time sys
> time bogo ops/s bogo ops/s
> stress-ng: info: [1246] (secs) (secs) (secs)
> (real time) (usr+sys time)
> stress-ng: info: [1246] msg 215174467 60.01 99.64
> 260.24 3585438.79 597906.15
> stress-ng: info: [1246] for a 60.02s run time:
> stress-ng: info: [1246] 360.10s available CPU time
> stress-ng: info: [1246] 99.72s user time ( 27.69%)
> stress-ng: info: [1246] 260.32s system time ( 72.29%)
> stress-ng: info: [1246] 360.04s total time ( 99.98%)
> stress-ng: info: [1246] load average: 7.98 2.33 0.80
>
> so if I'm reading this correctly, reverting the patches here brings the
> *slow-down*.
>
> What's up?
>
> reproducer:
> ----------
>
> #!/usr/bin/bash
>
> for cpu_dir in /sys/devices/system/cpu/cpu[0-9]*
> do
> online_file="$cpu_dir"/online
> [ -f "$online_file" ] && [ "$(cat "$online_file")" -eq 0 ] && continue
>
> file="$cpu_dir"/cpufreq/scaling_governor
> [ -f "$file" ] && echo "performance" > "$file"
> done
>
> stress-ng --timeout 60 --times --verify --metrics-brief --msg 9
The original test case is for 'nr_threads=10%' which turns to '9' for the
96 CPU 2-sockets Cascade Lake platform. So I guess it may not be reproduced
on 1 socket platform, and sometimes kernel config also matters for
micro-benchmark like 'stress-ng'
Thanks,
Feng
> --
> Regards/Gruss,
> Boris.
>
> SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG
> Nürnberg
