linux-kernel - Re: [PATCH v2] freezer,sched: Use saved_state to reduce some spurious wakeups

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Message-ID: <783c60ef-5341-7893-e9e8-2b1b249f89c9@quicinc.com>
Date:   Fri, 8 Sep 2023 15:30:43 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>, <kernel@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-pm@...r.kernel.org>,
        "Prakash Viswalingam" <quic_prakashv@...cinc.com>
Subject: Re: [PATCH v2] freezer,sched: Use saved_state to reduce some spurious
 wakeups



On 9/8/2023 3:08 PM, Peter Zijlstra wrote:
> On Fri, Sep 08, 2023 at 01:08:07PM -0700, Elliot Berman wrote:
> 
>>> Perhaps we should start off by doing the below, instead of making it
>>> more complicated instead. I suppose you're right about the overhead, but
>>> run a hackbench just to make sure or something.
>>>
>>
>> I ran perf bench sched message -g 40 -l 40 with the v3 patch [1]. After 60
>> iterations each, I don't see a significant difference on my arm64 platform:
>> both samples ~normal and ~eq variance w/t-test p-value: 0.79.
>>
>> We also ran typical high level benchmarks for our SoCs (antutu,
>> geekbench, et. al) and didn't see any regressions there.
> 
> So if you would've made this 2 patches, the first removing the ifdef,
> then the changelog for that patch would be a good place to mention it
> doesn't measurably regress things.

No problem, easily done.

> As a bonus, it then makes your other changes smaller too ;-)

Did you mean that each commit is smaller but overall delta is the same
or something else? I still wanted to update comments on saved_state in
kernel/sched/core.c as it gives good explanation of what is going on. I
have split the commit but want to make sure I make the changes you were
thinking :-)

Thanks,
Elliot