linux-kernel - Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY

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Message-ID: <CA+KHdyV9zh9wj6VsFVAt2R1G=q7is2=QyEF1EJbptRxaXr429A@mail.gmail.com>
Date:   Mon, 13 Feb 2017 18:17:12 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Uladzislau 2 Rezki <uladzislau2.rezki@...ymobile.com>
Subject: Re: [RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE

On Mon, Feb 13, 2017 at 2:51 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Feb 09, 2017 at 07:54:05PM +0100, Uladzislau Rezki wrote:
>
>> > Does this patch make an actual difference, if so how much and with
>> > what workload?
>> >
>> Yes, it does. I see a slight improvement when it comes to frame drops
>> (in my case drops per/two seconds). Basically a test case is left finger
>> swipe on the display (21 times, duration is 2 seconds + 1 second sleep
>> between iterations):
>>
>> 0   Framedrops:  7    5
>> 1   Framedrops:  5    3
>> 2   Framedrops:  8    5
>> 3   Framedrops:  4    5
>> 4   Framedrops:  3    3
>> 5   Framedrops:  6    4
>> 6   Framedrops:  3    2
>> 7   Framedrops:  3    4
>> 8   Framedrops:  5    3
>> 9   Framedrops:  3    3
>> 10 Framedrops:  7    4
>> 11 Framedrops:  3    4
>> 12 Framedrops:  3    3
>> 13 Framedrops:  3    3
>> 14 Framedrops:  3    5
>> 15 Framedrops:  7    3
>> 16 Framedrops:  5    3
>> 17 Framedrops:  3    2
>> 18 Framedrops:  5    3
>> 19 Framedrops:  4    3
>> 20 Framedrops:  3    2
>>
>> max is 8 vs 5; min is 2 vs 3.
>>
>> As for applied load, it is not significant and i would say is "light".
>
> So that is useful information that should have been in the Changelog.
>
> OK, can you respin this patch with adjusted Changelog and taking Mike's
> feedback?
>
Yes, i will prepare a patch accordingly, no problem.

>
> Also, I worry about the effects of this on !PREEMPT kernels, the first
> hunk (which explicitly states is about latency) should be under
> CONFIG_PREEMPT to match the similar case we already have in
> detach_tasks().
>
> But your second hunk, which ignores the actual load of tasks in favour
> of just moving _something_ already, is utterly dangerous if not coupled
> with these two other conditions, so arguably that too should be under
> CONFIG_PREEMPT.
>
I see your point. Will round both with CONFIG_PREEMPT.

--
Uladzislau Rezki