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

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Date:   Thu, 9 Feb 2017 19:54:05 +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 Thu, Feb 9, 2017 at 1:22 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Feb 08, 2017 at 09:43:29AM +0100, Uladzislau Rezki wrote:
>> From: Uladzislau 2 Rezki <uladzislau2.rezki@...ymobile.com>
>>
>> A load balancer calculates imbalance factor for particular shed
>> domain and tries to steal up the prescribed amount of weighted load.
>> However, a small imbalance factor would sometimes prevent us from
>> stealing any tasks at all. When a CPU is newly idle, it should
>> steal first task which passes a migration criteria.
>>

>
> So ideally we'd reduce the number of special cases instead of increase
> them.
>
I agree.

>
> 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".

--
Uladzislau Rezki