From: Joel Fernandes <joel@joelfernandes.org>
To: Youssef Esmat <youssefesmat@google.com>
Cc: Qais Yousef <qais.yousef@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
bristot@redhat.com, clark.williams@gmail.com,
bigeasy@linutronix.de, "Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: Sum of weights idea for CFS PI
Date: Fri, 30 Sep 2022 14:45:10 -0400 [thread overview]
Message-ID: <CAEXW_YQQ=CfQEOkXK-VFJtZTdY=_TsWz=Ndgg_BgJumFHJktkQ@mail.gmail.com> (raw)
In-Reply-To: <CALUeGD21QY+-6oLUztdecg5C8AX9xToxpGpxx5M5D9VnhSkVMg@mail.gmail.com>
On Fri, Sep 30, 2022 at 2:10 PM Youssef Esmat <youssefesmat@google.com> wrote:
[..]
> > > Hi Everyone!
> >
> > Hi Youssef,
> >
> > (Youssef is new to LKML though in no way new to OS or software development. I
> > gave him the usual 'dont-top-post' chat already - fyi).
> >
> > > I am not sure we should care about A's sleeping pattern. The case we
> > > care about is when A is running or wants to run but can't because it
> > > is blocked on C. In that case C should get the weight of A as if A was
> > > running.
> >
> > Just to clarify - Youssef did mean sum of weights of different things in the
> > chain, and not just weights (he confirmed on chat that that's what he meant).
> >
>
> Yeah thanks for clarifying, I meant that C should get the sum of
> weights as if A was running (3/5 in your example) since in this
> segment of time A would have been running if it was not blocked on the
> lock. I think it's safe to ignore the average and just use the sum of
For the onlooker, we are talking about the classical case of priority
inversion involving 3 tasks A, B and C which can be expanded to a
chain of tasks. Highest prio A blocks on a lock that lowest prio C
holds, while an unrelated medium prio B blocks C (or reduces progress
of it as in the case of CFS).
On the note of "A would have been running if it was not blocked on the
lock". I think that would be an assumption - we don't know if A would
be running. We only know the past, not the future. A could very well
make an I/O request for example. Hence there could be a need to use
A's past utilization, right?
thanks,
- Joel
next prev parent reply other threads:[~2022-09-30 18:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-29 20:38 Sum of weights idea for CFS PI Joel Fernandes
2022-09-30 13:49 ` Qais Yousef
2022-09-30 15:44 ` Youssef Esmat
2022-09-30 17:42 ` Joel Fernandes
2022-09-30 18:10 ` Youssef Esmat
2022-09-30 18:45 ` Joel Fernandes [this message]
2022-09-30 17:34 ` Joel Fernandes
2022-10-03 16:14 ` Qais Yousef
2022-10-03 16:27 ` Joel Fernandes
2022-10-04 16:30 ` Qais Yousef
2022-10-04 19:48 ` Joel Fernandes
2022-10-05 9:31 ` Qais Yousef
2022-10-04 20:27 ` Joel Fernandes
2022-10-05 10:04 ` Qais Yousef
2022-10-06 13:53 ` Joel Fernandes
2022-10-06 19:40 ` Youssef Esmat
2022-10-08 15:04 ` Joel Fernandes
2022-10-10 14:46 ` Qais Yousef
2022-10-10 15:11 ` Joel Fernandes
2022-10-12 14:30 ` Qais Yousef
2022-10-04 11:50 ` Sebastian Andrzej Siewior
2022-10-04 14:43 ` Joel Fernandes
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