From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
juri.lelli@redhat.com, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, corbet@lwn.net, qyousef@layalina.io,
chris.hyser@oracle.com, patrick.bellasi@matbug.net,
pjt@google.com, pavel@ucw.cz, qperret@google.com,
tim.c.chen@linux.intel.com, joshdon@google.com, timj@gnu.org,
kprateek.nayak@amd.com, yu.c.chen@intel.com,
youssefesmat@chromium.org, joel@joelfernandes.org, efault@gmx.de
Subject: Re: [PATCH 08/17] sched/fair: Implement an EEVDF like policy
Date: Tue, 4 Apr 2023 14:00:54 +0200 [thread overview]
Message-ID: <20230404120054.GV4253@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtD+EiB4mnRD0z4wYg6PDn1vLKxu4fxrgfiqsm2G3+RrEQ@mail.gmail.com>
On Thu, Mar 30, 2023 at 07:05:17PM +0200, Vincent Guittot wrote:
> On Thu, 30 Mar 2023 at 10:04, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Wed, Mar 29, 2023 at 04:35:25PM +0200, Vincent Guittot wrote:
> >
> > > IIUC how it works, Vd = ve + r / wi
> > >
> > > So for a same weight, the vd will be earlier but it's no more alway
> > > true for different weight
> >
> > Correct; but for a heavier task the time also goes slower and since it
> > needs more time, you want it to go first. But yes, this is weird at
> > first glance.
>
> Yeah, I understand that this is needed for bounding the lag to a
> quantum max but that makes the latency prioritization less obvious and
> not always aligned with what we want
That very much depends on what we want I suppose :-) So far there's not
been strong definitions of what we want, other than that we consider a
negative latency nice task to get it's slice a little earlier where
possible.
(also, I rather like that vagueness -- just like nice is rather vague,
it gives us room for interpretation when implementing things)
> let say that you have 2 tasks A and B waking up simultaneously with
> the same vruntime; A has a negative latency nice to reflect some
> latency constraint and B the default value. A will run 1st if they
> both have the same prio which is aligned with their latency nice
> values but B could run 1st if it increase its nice prio to reflect the
> need for a larger cpu bandwidth so you can defeat the purpose of the
> latency nice although there is no unfairness
>
> A cares of its latency and set a negative latency nice to reduce its
> request slice
This is true; but is it really a problem? It's all relative anyway :-)
Specifically, if you latency-nice harder than nice it, you win again,
also, nice is privilidged, while latency-nice is not (should it?)
The thing I like about EEVDF is that it actually makes the whole thing
simpler, it takes away a whole bunch of magic, and yes the latency thing
is perhaps more relative than absolute, but isn't that good enough?
That said; IIRC there's a few papers (which I can no longer find because
aparently google can now only give me my own patches and the opinion of
the internet on them when I search EEVDF :/) that muck with the {w,r}
set to build 'realtime' schedulers on top of EEVDF. So there's certainly
room to play around a bit.
next prev parent reply other threads:[~2023-04-04 12:01 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-28 9:26 [PATCH 00/17] sched: EEVDF using latency-nice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 01/17] sched: Introduce latency-nice as a per-task attribute Peter Zijlstra
2023-03-28 9:26 ` [PATCH 02/17] sched/fair: Add latency_offset Peter Zijlstra
2023-03-28 9:26 ` [PATCH 03/17] sched/fair: Add sched group latency support Peter Zijlstra
2023-03-28 9:26 ` [PATCH 04/17] sched/fair: Add avg_vruntime Peter Zijlstra
2023-03-28 23:57 ` Josh Don
2023-03-29 7:50 ` Peter Zijlstra
2023-04-05 19:13 ` Peter Zijlstra
2023-03-28 9:26 ` [PATCH 05/17] sched/fair: Remove START_DEBIT Peter Zijlstra
2023-03-28 9:26 ` [PATCH 06/17] sched/fair: Add lag based placement Peter Zijlstra
2023-04-03 9:18 ` Chen Yu
2023-04-05 9:47 ` Peter Zijlstra
2023-04-06 3:03 ` Chen Yu
2023-04-13 15:42 ` Chen Yu
2023-04-13 15:55 ` Chen Yu
2023-03-28 9:26 ` [PATCH 07/17] rbtree: Add rb_add_augmented_cached() helper Peter Zijlstra
2023-03-28 9:26 ` [PATCH 08/17] sched/fair: Implement an EEVDF like policy Peter Zijlstra
2023-03-29 1:26 ` Josh Don
2023-03-29 8:02 ` Peter Zijlstra
2023-03-29 8:06 ` Peter Zijlstra
2023-03-29 8:22 ` Peter Zijlstra
2023-03-29 18:48 ` Josh Don
2023-03-29 8:12 ` Peter Zijlstra
2023-03-29 18:54 ` Josh Don
2023-03-29 8:18 ` Peter Zijlstra
2023-03-29 14:35 ` Vincent Guittot
2023-03-30 8:01 ` Peter Zijlstra
2023-03-30 17:05 ` Vincent Guittot
2023-04-04 12:00 ` Peter Zijlstra [this message]
2023-03-28 9:26 ` [PATCH 09/17] sched: Commit to lag based placement Peter Zijlstra
2023-03-28 9:26 ` [PATCH 10/17] sched/smp: Use lag to simplify cross-runqueue placement Peter Zijlstra
2023-03-28 9:26 ` [PATCH 11/17] sched: Commit to EEVDF Peter Zijlstra
2023-03-28 9:26 ` [PATCH 12/17] sched/debug: Rename min_granularity to base_slice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 13/17] sched: Merge latency_offset into slice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 14/17] sched/eevdf: Better handle mixed slice length Peter Zijlstra
2023-03-31 15:26 ` Vincent Guittot
2023-04-04 9:29 ` Peter Zijlstra
2023-04-04 13:50 ` Joel Fernandes
2023-04-05 5:41 ` Mike Galbraith
2023-04-05 8:35 ` Peter Zijlstra
2023-04-05 20:05 ` Joel Fernandes
2023-04-14 11:18 ` Phil Auld
2023-04-16 5:10 ` Joel Fernandes
[not found] ` <20230401232355.336-1-hdanton@sina.com>
2023-04-02 2:40 ` Mike Galbraith
2023-03-28 9:26 ` [PATCH 15/17] [RFC] sched/eevdf: Sleeper bonus Peter Zijlstra
2023-03-29 9:10 ` Mike Galbraith
2023-03-28 9:26 ` [PATCH 16/17] [RFC] sched/eevdf: Minimal vavg option Peter Zijlstra
2023-03-28 9:26 ` [PATCH 17/17] [DEBUG] sched/eevdf: Debug / validation crud Peter Zijlstra
2023-04-03 7:42 ` [PATCH 00/17] sched: EEVDF using latency-nice Shrikanth Hegde
2023-04-10 3:13 ` David Vernet
2023-04-11 2:09 ` David Vernet
[not found] ` <20230410082307.1327-1-hdanton@sina.com>
2023-04-11 10:15 ` Mike Galbraith
[not found] ` <20230411133333.1790-1-hdanton@sina.com>
2023-04-11 14:56 ` Mike Galbraith
[not found] ` <20230412025042.1413-1-hdanton@sina.com>
2023-04-12 4:05 ` Mike Galbraith
2023-04-25 12:32 ` Phil Auld
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