From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
dietmar.eggemann@arm.com, Morten.Rasmussen@arm.com,
yuyang.du@intel.com, pjt@google.com, bsegall@google.com
Subject: Re: [PATCH v2] sched/fair: update scale invariance of PELT
Date: Tue, 11 Apr 2017 10:53:05 +0200 [thread overview]
Message-ID: <20170411085305.aik6gdy6n3wa22ok@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170411075221.GA30421@linaro.org>
On Tue, Apr 11, 2017 at 09:52:21AM +0200, Vincent Guittot wrote:
> Le Monday 10 Apr 2017 à 19:38:02 (+0200), Peter Zijlstra a écrit :
> >
> > Thanks for the rebase.
> >
> > On Mon, Apr 10, 2017 at 11:18:29AM +0200, Vincent Guittot wrote:
> >
> > Ok, so let me try and paraphrase what this patch does.
> >
> > So consider a task that runs 16 out of our 32ms window:
> >
> > running idle
> > |---------|---------|
> >
> >
> > You're saying that when we scale running with the frequency, suppose we
> > were at 50% freq, we'll end up with:
> >
> > run idle
> > |----|---------|
> >
> >
> > Which is obviously a shorter total then before; so what you do is add
> > back the lost idle time like:
> >
> > run lost idle
> > |----|----|---------|
> >
> >
> > to arrive at the same total time. Which seems to make sense.
>
> Yes
OK, bear with me.
So we have:
util_sum' = utilsum * y^p +
p-1
d1 * y^p + 1024 * \Sum y^n + d3 * y^0
n=1
For the unscaled version, right?
Now for the scaled version, instead of adding a full 'd1,d2,d3' running
segments, we want to add partially running segments, where r=f*d/f_max,
and lost segments l=d-r to fill out the idle time.
But afaict we then end up with (F=f/f_max):
util_sum' = utilsum * y^p +
p-1
F * d1 * y^p + F * 1024 * \Sum y^n + F * d3 * y^0
n=1
And we can collect the common term F:
util_sum' = utilsum * y^p +
p-1
F * (d1 * y^p + 1024 * \Sum y^n + d3 * y^0)
n=1
Which is exactly what we already did.
So now I'm confused. Where did I go wrong?
Because by scaling the contribution we get the exact result of doing the
smaller 'running' + 'lost' segments.
next prev parent reply other threads:[~2017-04-11 8:53 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-10 9:18 [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot
2017-04-10 17:38 ` Peter Zijlstra
2017-04-11 7:52 ` Vincent Guittot
2017-04-11 8:53 ` Peter Zijlstra [this message]
2017-04-11 9:40 ` Vincent Guittot
2017-04-11 10:41 ` Peter Zijlstra
2017-04-11 10:49 ` Peter Zijlstra
2017-04-11 13:09 ` Vincent Guittot
2017-04-12 11:28 ` Peter Zijlstra
2017-04-12 14:50 ` Vincent Guittot
2017-04-12 15:44 ` Peter Zijlstra
2017-04-13 9:42 ` Vincent Guittot
2017-04-13 13:32 ` Peter Zijlstra
2017-04-13 14:59 ` Vincent Guittot
2017-04-13 18:06 ` Peter Zijlstra
2017-04-14 8:47 ` Vincent Guittot
2017-04-11 12:08 ` Vincent Guittot
2017-04-11 9:12 ` Peter Zijlstra
2017-04-11 9:46 ` Vincent Guittot
2017-04-13 13:39 ` Peter Zijlstra
2017-04-13 15:16 ` Vincent Guittot
2017-04-13 16:13 ` Peter Zijlstra
2017-04-14 8:49 ` Vincent Guittot
2017-04-19 16:31 ` Vincent Guittot
2017-04-28 15:52 ` Morten Rasmussen
2017-04-28 17:08 ` Dietmar Eggemann
2017-05-03 17:11 ` Vincent Guittot
2017-04-28 22:09 ` Peter Zijlstra
2017-05-01 9:00 ` Peter Zijlstra
2017-05-02 13:38 ` Vincent Guittot
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