Re: [linux-next:master] [mm] f1a7941243: unixbench.score -5.1% regression

[Huang, Ying]

Shakeel Butt <shakeelb@xxxxxxxxxx> writes:

> On Sun, Dec 4, 2022 at 9:56 PM kernel test robot <yujie.liu@xxxxxxxxx> wrote:
>>
>> Greeting,
>>
>> FYI, we noticed a -5.1% regression of unixbench.score due to commit:
>>
> [...]
>> 9cd6ffa60256e931 f1a7941243c102a44e8847e3b94
>> ---------------- ---------------------------
>>          %stddev     %change         %stddev
>>              \          |                \
>>       7917            -5.1%       7509        unixbench.score
>
> What is unixbench.score?

Should be benchmark throughput.

>>      10485           -12.1%       9216        unixbench.time.maximum_resident_set_size

This should reflect accuracy change of per_cpu_counter.

>>   37236706            -5.1%   35324104        unixbench.time.minor_page_faults

The reduction is same as benchmark score.  So I think this reflect the
nature of time-bound testing (instead of workload-bound).

> For above two, is negative change good or bad?
>
>>       0.98 ą 20%      +0.7        1.64 ą 38%  perf-profile.calltrace.cycles-pp.link_path_walk.path_openat.do_filp_open.do_sys_openat2.__x64_sys_openat
>>       2.12 ą 19%      +0.8        2.96 ą 13%  perf-profile.calltrace.cycles-pp.handle_mm_fault.do_user_addr_fault.exc_page_fault.asm_exc_page_fault
>>       2.35 ą 13%      +0.9        3.28 ą 13%  perf-profile.calltrace.cycles-pp.__handle_mm_fault.handle_mm_fault.do_user_addr_fault.exc_page_fault.asm_exc_page_fault
>>       0.14 ą 74%      +0.4        0.55 ą 32%  perf-profile.children.cycles-pp.do_task_dead
>>       0.04 ą223%      +0.4        0.47 ą 49%  perf-profile.children.cycles-pp.__mmdrop
>
> Also how should I interpret the above perf-profiles?

It appears that the changes of handle_mm_fault() and __mmdrop() are
related to the code of the commit?  That is, for this specific workloads
(not so unpractical), the operations become slower?

Best Regards,
Huang, Ying