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,
tglx@linutronix.de
Subject: Re: [RFC][PATCH 13/15] sched/fair: Implement latency-nice
Date: Thu, 8 Jun 2023 14:44:40 +0200 [thread overview]
Message-ID: <20230608124440.GB1002251@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230608103458.GI998233@hirez.programming.kicks-ass.net>
On Thu, Jun 08, 2023 at 12:34:58PM +0200, Peter Zijlstra wrote:
> > Then asking for a request shorter than the tick also means that
> > scheduler must enqueue a new request (on behalf of the task) during
> > the tick and evaluate if the task is still the one to be scheduled
> > now.
>
> If there is no 'interrupt', we won't update time and the scheduler can't
> do anything -- as you well know. The paper only requires (and we
> slightly violate this) to push forward the deadline. See the comment
> with update_deadline().
>
> Much like pure EDF without a combined CBS.
>
> > So similarly to q, the request size r should be at least a tick
> > in order to reevaluate which task will run next after the end of a
> > request. In fact, the real limit is : r/wi >= tick/(Sum wj)
>
> > We can always not follow these assumptions made in the publication but
> > I wonder how we can then rely on its theorems and corollaries
>
> Again, I'm not entirely following, the corollaries take r_i < q into
> account, that's where the max(rmax, q) term comes from.
>
> You're right in that r_i < q does not behave 'right', but it doesn't
> invalidate the results. Note that if a task overshoots, it will build of
> significant negative lag (right side of the tree) and won't be eligible
> for it's next actual period. This 'hole' in the schedule is then used to
> make up for the extra time it used previously.
So notably, if your task *does* behave correctly and does not consume
the full request, then it will not build up (large) negative lag and
wakeup-preemption can make it go quickly on the next period.
This is where that FUDGE hack comes in, except I got it wrong, I think
it needs to be something like:
if (delta / W >= vslice) {
se->vlag += vslice
if (se->vlag > 0)
se->vlag = 0;
}
To ensure it can't gain time. It's still a gruesome hack, but at least
is shouldn't be able to game the system.
next prev parent reply other threads:[~2023-06-08 12:46 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-31 11:58 [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr Peter Zijlstra
2023-05-31 11:58 ` [PATCH 01/15] sched/fair: Add avg_vruntime Peter Zijlstra
2023-06-02 13:51 ` Vincent Guittot
2023-06-02 14:27 ` Peter Zijlstra
2023-06-05 7:18 ` Vincent Guittot
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Add cfs_rq::avg_vruntime tip-bot2 for Peter Zijlstra
2023-10-11 4:15 ` [PATCH 01/15] sched/fair: Add avg_vruntime Abel Wu
2023-10-11 7:30 ` Peter Zijlstra
2023-10-11 8:30 ` Abel Wu
2023-10-11 9:45 ` Peter Zijlstra
2023-10-11 10:05 ` Peter Zijlstra
2023-10-11 13:08 ` Peter Zijlstra
2023-05-31 11:58 ` [PATCH 02/15] sched/fair: Remove START_DEBIT Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Remove sched_feat(START_DEBIT) tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 03/15] sched/fair: Add lag based placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-10-11 12:00 ` [PATCH 03/15] " Abel Wu
2023-10-11 13:24 ` Peter Zijlstra
2023-10-12 7:04 ` Abel Wu
2023-10-13 7:37 ` Peter Zijlstra
2023-10-13 8:14 ` Abel Wu
2023-10-12 19:15 ` Benjamin Segall
2023-10-12 22:34 ` Peter Zijlstra
2023-10-13 16:35 ` Peter Zijlstra
2023-10-14 8:08 ` Mike Galbraith
2023-10-13 14:34 ` Peter Zijlstra
2023-05-31 11:58 ` [PATCH 04/15] rbtree: Add rb_add_augmented_cached() helper Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 05/15] sched/fair: Implement an EEVDF like policy Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: Implement an EEVDF-like scheduling policy tip-bot2 for Peter Zijlstra
2023-09-29 21:40 ` [PATCH 05/15] sched/fair: Implement an EEVDF like policy Benjamin Segall
2023-10-02 17:39 ` Peter Zijlstra
2023-10-11 4:14 ` Abel Wu
2023-10-11 7:33 ` Peter Zijlstra
2023-10-11 11:49 ` Abel Wu
2023-09-30 0:09 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Benjamin Segall
2023-10-03 10:42 ` [tip: sched/urgent] sched/fair: Fix pick_eevdf() tip-bot2 for Benjamin Segall
[not found] ` <CGME20231004203940eucas1p2f73b017497d1f4239a6e236fdb6019e2@eucas1p2.samsung.com>
2023-10-04 20:39 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Marek Szyprowski
2023-10-09 7:53 ` [tip: sched/urgent] sched/eevdf: Fix pick_eevdf() tip-bot2 for Benjamin Segall
2023-10-11 12:12 ` [PATCH] sched/fair: fix pick_eevdf to always find the correct se Abel Wu
2023-10-11 13:14 ` Peter Zijlstra
2023-10-12 10:04 ` Abel Wu
2023-10-11 21:01 ` Benjamin Segall
2023-10-12 10:25 ` Abel Wu
2023-10-12 17:51 ` Benjamin Segall
2023-10-13 3:46 ` Abel Wu
2023-10-13 16:51 ` Benjamin Segall
2023-05-31 11:58 ` [PATCH 06/15] sched: Commit to lag based placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/fair: " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 07/15] sched/smp: Use lag to simplify cross-runqueue placement Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-09-12 15:32 ` [PATCH 07/15] " Sebastian Andrzej Siewior
2023-09-13 9:03 ` Peter Zijlstra
2023-10-04 1:17 ` [PATCH] sched/fair: Preserve PLACE_DEADLINE_INITIAL deadline Daniel Jordan
2023-10-04 13:09 ` [PATCH v2] " Daniel Jordan
2023-10-04 15:46 ` Chen Yu
2023-10-06 16:31 ` Daniel Jordan
2023-10-12 4:48 ` K Prateek Nayak
2023-10-05 5:56 ` [PATCH] " K Prateek Nayak
2023-10-06 16:35 ` Daniel Jordan
2023-10-06 16:48 ` [PATCH] sched/fair: Always update_curr() before placing at enqueue Daniel Jordan
2023-10-06 19:58 ` Peter Zijlstra
2023-10-18 0:43 ` Daniel Jordan
2023-10-16 5:39 ` K Prateek Nayak
2023-05-31 11:58 ` [PATCH 08/15] sched: Commit to EEVDF Peter Zijlstra
2023-06-16 21:23 ` Joel Fernandes
2023-06-22 12:01 ` Ingo Molnar
2023-06-22 13:11 ` Joel Fernandes
2023-08-10 7:10 ` [tip: sched/core] sched/fair: " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 09/15] sched/debug: Rename min_granularity to base_slice Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] sched/debug: Rename sysctl_sched_min_granularity to sysctl_sched_base_slice tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 10/15] sched/fair: Propagate enqueue flags into place_entity() Peter Zijlstra
2023-08-10 7:10 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2023-05-31 11:58 ` [PATCH 11/15] sched/eevdf: Better handle mixed slice length Peter Zijlstra
2023-06-02 13:45 ` Vincent Guittot
2023-06-02 15:06 ` Peter Zijlstra
2023-06-10 6:34 ` Chen Yu
2023-06-10 11:22 ` Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 12/15] sched: Introduce latency-nice as a per-task attribute Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 13/15] sched/fair: Implement latency-nice Peter Zijlstra
2023-06-06 14:54 ` Vincent Guittot
2023-06-08 10:34 ` Peter Zijlstra
2023-06-08 12:44 ` Peter Zijlstra [this message]
2023-10-11 23:24 ` Benjamin Segall
2023-05-31 11:58 ` [RFC][PATCH 14/15] sched/fair: Add sched group latency support Peter Zijlstra
2023-05-31 11:58 ` [RFC][PATCH 15/15] sched/eevdf: Use sched_attr::sched_runtime to set request/slice Peter Zijlstra
2023-06-01 13:55 ` Vincent Guittot
2023-06-08 11:52 ` Peter Zijlstra
2023-08-24 0:52 ` [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr Daniel Jordan
2023-09-06 13:13 ` Peter Zijlstra
2023-09-29 16:54 ` Youssef Esmat
2023-10-02 15:55 ` Youssef Esmat
2023-10-02 18:41 ` Peter Zijlstra
2023-10-05 12:05 ` Peter Zijlstra
2023-10-05 14:14 ` Peter Zijlstra
2023-10-05 14:42 ` Peter Zijlstra
2023-10-05 18:23 ` Youssef Esmat
2023-10-06 0:36 ` Youssef Esmat
2023-10-10 8:08 ` Peter Zijlstra
2023-10-07 22:04 ` Peter Zijlstra
2023-10-09 14:41 ` Peter Zijlstra
2023-10-10 0:51 ` Youssef Esmat
2023-10-10 8:01 ` Peter Zijlstra
2023-10-16 16:50 ` Peter Zijlstra
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