From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: Chen Yu <yu.c.chen@intel.com>
Cc: peterz@infradead.org, bristot@redhat.com, bsegall@google.com,
chris.hyser@oracle.com, corbet@lwn.net, dietmar.eggemann@arm.com,
efault@gmx.de, joel@joelfernandes.org, joshdon@google.com,
juri.lelli@redhat.com, kprateek.nayak@amd.com,
linux-kernel@vger.kernel.org, mgorman@suse.de, mingo@kernel.org,
patrick.bellasi@matbug.net, pavel@ucw.cz, pjt@google.com,
qperret@google.com, qyousef@layalina.io, rostedt@goodmis.org,
tglx@linutronix.de, tim.c.chen@linux.intel.com, timj@gnu.org,
vincent.guittot@linaro.org, youssefesmat@chromium.org,
yu.chen.surf@gmail.com
Subject: Re: [PATCH v2] sched/fair: Preserve PLACE_DEADLINE_INITIAL deadline
Date: Fri, 6 Oct 2023 12:31:46 -0400 [thread overview]
Message-ID: <dqrnrq4atsbfu2ftgnw563ovrg7p4i2t3vpjerqs5xezhy3omj@ixdkxq3y66ss> (raw)
In-Reply-To: <ZR2IzepAXhxnsqLp@chenyu5-mobl2.ccr.corp.intel.com>
Hi Chenyu,
On Wed, Oct 04, 2023 at 11:46:21PM +0800, Chen Yu wrote:
> Hi Daniel,
>
> On 2023-10-04 at 09:09:08 -0400, Daniel Jordan wrote:
> > An entity is supposed to get an earlier deadline with
> > PLACE_DEADLINE_INITIAL when it's forked, but the deadline gets
> > overwritten soon after in enqueue_entity() the first time a forked
> > entity is woken so that PLACE_DEADLINE_INITIAL is effectively a no-op.
> >
> > Placing in task_fork_fair() seems unnecessary since none of the values
> > that get set (slice, vruntime, deadline) are used before they're set
> > again at enqueue time, so get rid of that (and with it all of
> > task_fork_fair()) and just pass ENQUEUE_INITIAL to enqueue_entity() via
> > wake_up_new_task().
> >
> > Fixes: e8f331bcc270 ("sched/smp: Use lag to simplify cross-runqueue placement")
> > Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> > ---
> >
> > v2
> > - place_entity() seems like the only reason for task_fork_fair() to exist
> > after the recent removal of sysctl_sched_child_runs_first, so take out
> > the whole function.
>
> At first glance I thought if we remove task_fork_fair(), do we lose one chance to
> update the parent task's statistic in update_curr()? We might get out-of-date
> parent task's deadline and make preemption decision based on the stale data in
> wake_up_new_task() -> wakeup_preempt() -> pick_eevdf(). But after a second thought,
> I found that wake_up_new_task() -> enqueue_entity() itself would invoke update_curr(),
> so this should not be a problem.
>
> Then I was wondering why can't we just skip place_entity() in enqueue_entity()
> if ENQUEUE_WAKEUP is not set, just like the code before e8f331bcc270? In this
> way the new fork task's deadline will not be overwritten by wake_up_new_task()->
> enqueue_entity(). Then I realized that, after e8f331bcc270, the task's vruntime
> and deadline are all calculated by place_entity() rather than being renormalised
> to cfs_rq->min_vruntime in enqueue_entity(), so we can not simply skip place_entity()
> in enqueue_entity().
This all made me wonder if the order of update_curr() for the parent and
place_entity() for the child matters. And it does, since placing uses
avg_vruntime(), which wants an up-to-date vruntime for current and
min_vruntime for cfs_rq. Good that 'curr' in enqueue_entity() is false
on fork so that the parent's vruntime is up to date, but it seems
placing should always happen after update_curr().
> Per my understanding, this patch looks good,
>
> Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Thanks!
Daniel
next prev parent reply other threads:[~2023-10-06 16:32 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 [this message]
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
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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