Re: [tip:timers/core] [posix] 1535cb8028: stress-ng.epoll.ops_per_sec 36.2% regression

[Thomas Gleixner]

On Thu, Mar 27 2025 at 07:21, Eric Dumazet wrote:
> On Wed, Mar 26, 2025 at 10:11 PM Mateusz Guzik <mjguzik@xxxxxxxxx> wrote:
>> On Wed, Mar 26, 2025 at 09:07:51AM +0100, Thomas Gleixner wrote:
>> > Unfortunately I can't reproduce any of it. I checked the epoll test
>> > source and it uses a posix timer, but that commit makes the hash less
>> > contended so there is zero explanation.
>> >
>>
>> The short summary is:
>> 1. your change is fine
>
> Let me rephrase this.
>
> Absolutely wonderful series, thanks a lot Thomas for doing it.

Thank you!

> Next bottlenecks are now these ones, but showing up in synthetic
> benchmarks only.

Right. I saw them too when working on this.

>     33.36%  timer_storm      [kernel.kallsyms]           [k]
> inc_rlimit_get_ucounts
>
>     32.85%  timer_storm      [kernel.kallsyms]           [k]
> dec_rlimit_put_ucounts

These two are not really posix-timer specific. They are also the
standouts for any signal micro benchmark.

I stared at the implementation a bit, but there is not much we can do
about that I fear.

Thanks,

        tglx