Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 6 Nov 2019 17:41:35 +0000
From:   Qais Yousef <qais.yousef@arm.com>
To:     Thara Gopinath <thara.gopinath@linaro.org>
Cc:     mingo@redhat.com, peterz@infradead.org, ionela.voinescu@arm.com,
        vincent.guittot@linaro.org, rui.zhang@intel.com,
        edubezval@gmail.com, qperret@google.com,
        linux-kernel@vger.kernel.org, amit.kachhap@gmail.com,
        javi.merino@kernel.org, daniel.lezcano@linaro.org
Subject: Re: [Patch v5 4/6] sched/fair: update cpu_capcity to reflect thermal
 pressure
Message-ID: <20191106174135.gsmnwpwxfarywded@e107158-lin.cambridge.arm.com>
References: <1572979786-20361-1-git-send-email-thara.gopinath@linaro.org>
 <1572979786-20361-5-git-send-email-thara.gopinath@linaro.org>
 <20191106165646.vc7j4hbhj2hcrku4@e107158-lin.cambridge.arm.com>
 <5DC30371.1000209@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <5DC30371.1000209@linaro.org>
User-Agent: NeoMutt/20171215
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 11/06/19 12:31, Thara Gopinath wrote:
> On 11/06/2019 11:56 AM, Qais Yousef wrote:
> > On 11/05/19 13:49, Thara Gopinath wrote:
> >> cpu_capacity relflects the maximum available capacity of a cpu. Thermal
> >> pressure on a cpu means this maximum available capacity is reduced. This
> >> patch reduces the average thermal pressure for a cpu from its maximum
> >> available capacity so that cpu_capacity reflects the actual
> >> available capacity.
> >>
> >> Other signals that are deducted from cpu_capacity to reflect the actual
> >> capacity available are rt and dl util_avg. util_avg tracks a binary signal
> >> and uses the weights 1024 and 0. Whereas thermal pressure is tracked
> >> using load_avg. load_avg uses the actual "delta" capacity as the weight.
> > 
> > I think you intended to put this as comment...
> > 
> >>
> >> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> >> ---
> >>  kernel/sched/fair.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index 9fb0494..5f6c371 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -7738,6 +7738,7 @@ static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
> >>  
> >>  	used = READ_ONCE(rq->avg_rt.util_avg);
> >>  	used += READ_ONCE(rq->avg_dl.util_avg);
> >> +	used += READ_ONCE(rq->avg_thermal.load_avg);
> > 
> > ... here?
> 
> I did not!  But I can.
> > 
> > I find the explanation hard to parse too. Do you think you can rephrase it?
> > Something based on what you wrote here would be more understandable IMHO:
> > https://lore.kernel.org/lkml/5DBB05BC.40502@linaro.org/
> I will try to rephrase it! I am sorry that you found it hard to parse.
> Honestly, I cannot copy paste the code snippet I pointed out to you here
> in comment.(And I think that is the reason you found it easier to
> understand) But I will try my best to put it in words.

No worries. The problem could be me :-)

But a comment in the code is very important as util_avg + load_avg is confusing
without a comment. I wouldn't expect both signal to be compatible but the
thermal one is special. A comment explaining why it's special is all we need.


Thanks

--
Qais Yousef