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

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Message-ID: <8b917006-2c77-0b36-060a-76a1ca04d2e0@quicinc.com>
Date:   Fri, 8 Sep 2023 16:17:09 -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 3:48 PM, Peter Zijlstra wrote:
> On Fri, Sep 08, 2023 at 03:30:43PM -0700, Elliot Berman wrote:
>>
>>
>> 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? 
> 
> That.
> 
>> 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 :-)
> 
> well, it's nearly 1am, I'm not thinking very much :-) Changing those
> comments seems fine when you add the freezer thing.

I was wondering what time zone you are in, I saw your previous replies
are early in my morning. I think you are giving Greg a run for his money
with responses at all hours :-) 

I sent v4 with the changes split:
https://lore.kernel.org/all/20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com/