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Subject: Re: [PATCH] sched/fair: Update rq_clock, cfs_rq before migrating for
 asym cpu capacity
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Dietmar Eggemann <Dietmar.Eggemann@arm.com>
References: <20190709115759.10451-1-chris.redpath@arm.com>
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From:   Chris Redpath <chris.redpath@foss.arm.com>
Message-ID: <1128a866-6817-3703-8962-8c3670dd10c1@foss.arm.com>
Date:   Tue, 9 Jul 2019 16:42:07 +0100
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On 09/07/2019 16:36, Vincent Guittot wrote:
> Hi Chris,
> 
>>
>> We enter this code quite often in our testing, most individual runs of a
>> test which has small tasks involved have at least one hit where we make
>> a change to the clock with this patch in.
> 
> Do you have a rt-app file that you can share ?
> 

The ThreeSmallTasks test which is the worst hit produces this:

{
     "tasks": {
         "small_0": {
             "policy": "SCHED_OTHER",
             "delay": 0,
             "loop": 1,
             "phases": {
                 "p000001": {
                     "loop": 62,
                     "run": 2880,
                     "timer": {
                         "ref": "small_0",
                         "period": 16000
                     }
                 }
             }
         },
         "small_1": {
             "policy": "SCHED_OTHER",
             "delay": 0,
             "loop": 1,
             "phases": {
                 "p000001": {
                     "loop": 62,
                     "run": 2880,
                     "timer": {
                         "ref": "small_1",
                         "period": 16000
                     }
                 }
             }
         },
         "small_2": {
             "policy": "SCHED_OTHER",
             "delay": 0,
             "loop": 1,
             "phases": {
                 "p000001": {
                     "loop": 62,
                     "run": 2880,
                     "timer": {
                         "ref": "small_2",
                         "period": 16000
                     }
                 }
             }
         }
     },
     "global": {
         "default_policy": "SCHED_OTHER",
         "duration": -1,
         "calibration": 264,
         "logdir": "/root/devlib-target"
     }
}

when I run it

>>
>> That said - despite the relatively high number of hits only about 5% of
>> runs see enough additional energy consumed to trigger a test failure. We
>> do try to keep a quiet system as much as possible and only run for a few
>> seconds so the impact we see in testing is also probably higher than in
>> the real world.
> 
> Yeah, I'm curious to see the impact on a real system which have a
> 60fps screen update like an android phone
> 

I wouldn't expect much change there but I would on the idle-ish 
homescreen/day-of-use type benchmarks.

If I had a platform with any kind of representative energy use, I'd test 
it :)