From: Aaron Lu <aaron.lwe@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Vineeth Remanan Pillai" <vpillai@digitalocean.com>,
"Nishanth Aravamudan" <naravamudan@digitalocean.com>,
"Julien Desfossez" <jdesfossez@digitalocean.com>,
"Tim Chen" <tim.c.chen@linux.intel.com>,
"Ingo Molnar" <mingo@kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Paul Turner" <pjt@google.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Aaron Lu" <aaron.lu@linux.alibaba.com>,
"Linux List Kernel Mailing" <linux-kernel@vger.kernel.org>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Kees Cook" <keescook@chromium.org>,
"Greg Kerr" <kerrnel@google.com>, "Phil Auld" <pauld@redhat.com>,
"Aubrey Li" <aubrey.intel@gmail.com>,
"Li, Aubrey" <aubrey.li@linux.intel.com>,
"Valentin Schneider" <valentin.schneider@arm.com>,
"Mel Gorman" <mgorman@techsingularity.net>,
"Pawan Gupta" <pawan.kumar.gupta@linux.intel.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Joel Fernandes" <joelaf@google.com>,
"Joel Fernandes" <joel@joelfernandes.org>
Subject: Re: [PATCH updated v2] sched/fair: core wide cfs task priority comparison
Date: Fri, 22 May 2020 17:40:19 +0800 [thread overview]
Message-ID: <20200522094019.GA8245@aaronlu-desktop> (raw)
In-Reply-To: <20200516034230.GA72980@aaronlu-desktop>
On Sat, May 16, 2020 at 11:42:30AM +0800, Aaron Lu wrote:
> On Thu, May 14, 2020 at 03:02:48PM +0200, Peter Zijlstra wrote:
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4476,6 +4473,16 @@ next_class:;
> > WARN_ON_ONCE(!cookie_match(next, rq_i->core_pick));
> > }
> >
> > + /* XXX SMT2 only */
> > + if (new_active == 1 && old_active > 1) {
>
> There is a case when incompatible task appears but we failed to 'drop
> into single-rq mode' per the above condition check. The TLDR is: when
> there is a task that sits on the sibling rq with the same cookie as
> 'max', new_active will be 2 instead of 1 and that would cause us missing
> the chance to do a sync of core min_vruntime.
FWIW: when I disable the feature of running cookie_pick task on sibling
and thus enforce a strict single-rq mode, Peter's patch works well for
the scenario described below.
> This is how it happens:
> 1) 2 tasks of the same cgroup with different weight running on 2 siblings,
> say cg0_A with weight 1024 bound at cpu0 and cg0_B with weight 2 bound
> at cpu1(assume cpu0 and cpu1 are siblings);
> 2) Since new_active == 2, we didn't trigger min_vruntime sync. For
> simplicity, let's assume both siblings' root cfs_rq's min_vruntime and
> core_vruntime are all at 0 now;
> 3) let the two tasks run a while;
> 4) a new task cg1_C of another cgroup gets queued on cpu1. Since cpu1's
> existing task has a very small weight, its cfs_rq's min_vruntime can
> be much larger than cpu0's cfs_rq min_vruntime. So cg1_C's vruntime is
> much larger than cg0_A's and the 'max' of the core wide task
> selection goes to cg0_A;
> 5) Now I suppose we should drop into single-rq mode and by doing a sync
> of core min_vruntime, cg1_C's turn shall come. But the problem is, our
> current selection logic prefer not to waste CPU time so after decides
> cg0_A as the 'max', the sibling will also do a cookie_pick() and
> get cg0_B to run. This is where problem asises: new_active is 2
> instead of the expected 1.
> 6) Due to we didn't do the sync of core min_vruntime, the newly queued
> cg1_C shall wait a long time before cg0_A's vruntime catches up.
P.S. this is what I did to enforce a strict single-rq mode:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1fa5b48b742a..0f5580bc7e96 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4411,7 +4411,7 @@ pick_task(struct rq *rq, const struct sched_class *class, struct task_struct *ma
(!max || prio_less(max, class_pick)))
return class_pick;
- return cookie_pick;
+ return NULL;
}
static struct task_struct *
next prev parent reply other threads:[~2020-05-22 9:40 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-04 16:59 [RFC PATCH 00/13] Core scheduling v5 vpillai
2020-03-04 16:59 ` [RFC PATCH 01/13] sched: Wrap rq::lock access vpillai
2020-03-04 16:59 ` [RFC PATCH 02/13] sched: Introduce sched_class::pick_task() vpillai
2020-03-04 16:59 ` [RFC PATCH 03/13] sched: Core-wide rq->lock vpillai
2020-04-01 11:42 ` [PATCH] sched/arm64: store cpu topology before notify_cpu_starting Cheng Jian
2020-04-01 13:23 ` Valentin Schneider
2020-04-06 8:00 ` chengjian (D)
2020-04-09 9:59 ` Sudeep Holla
2020-04-09 10:32 ` Valentin Schneider
2020-04-09 11:08 ` Sudeep Holla
2020-04-09 17:54 ` Joel Fernandes
2020-04-10 13:49 ` chengjian (D)
2020-04-14 11:36 ` [RFC PATCH 03/13] sched: Core-wide rq->lock Peter Zijlstra
2020-04-14 21:35 ` Vineeth Remanan Pillai
2020-04-15 10:55 ` Peter Zijlstra
2020-04-14 14:32 ` Peter Zijlstra
2020-03-04 16:59 ` [RFC PATCH 04/13] sched/fair: Add a few assertions vpillai
2020-03-04 16:59 ` [RFC PATCH 05/13] sched: Basic tracking of matching tasks vpillai
2020-03-04 16:59 ` [RFC PATCH 06/13] sched: Update core scheduler queue when taking cpu online/offline vpillai
2020-03-04 16:59 ` [RFC PATCH 07/13] sched: Add core wide task selection and scheduling vpillai
2020-04-14 13:35 ` Peter Zijlstra
2020-04-16 23:32 ` Tim Chen
2020-04-17 10:57 ` Peter Zijlstra
2020-04-16 3:39 ` Chen Yu
2020-04-16 19:59 ` Vineeth Remanan Pillai
2020-04-17 11:18 ` Peter Zijlstra
2020-04-19 15:31 ` Chen Yu
2020-05-21 23:14 ` Joel Fernandes
2020-05-21 23:16 ` Joel Fernandes
2020-05-22 2:35 ` Joel Fernandes
2020-05-22 3:44 ` Aaron Lu
2020-05-22 20:13 ` Joel Fernandes
2020-03-04 16:59 ` [RFC PATCH 08/13] sched/fair: wrapper for cfs_rq->min_vruntime vpillai
2020-03-04 16:59 ` [RFC PATCH 09/13] sched/fair: core wide vruntime comparison vpillai
2020-04-14 13:56 ` Peter Zijlstra
2020-04-15 3:34 ` Aaron Lu
2020-04-15 4:07 ` Aaron Lu
2020-04-15 21:24 ` Vineeth Remanan Pillai
2020-04-17 9:40 ` Aaron Lu
2020-04-20 8:07 ` [PATCH updated] sched/fair: core wide cfs task priority comparison Aaron Lu
2020-04-20 22:26 ` Vineeth Remanan Pillai
2020-04-21 2:51 ` Aaron Lu
2020-04-24 14:24 ` [PATCH updated v2] " Aaron Lu
2020-05-06 14:35 ` Peter Zijlstra
2020-05-08 8:44 ` Aaron Lu
2020-05-08 9:09 ` Peter Zijlstra
2020-05-08 12:34 ` Aaron Lu
2020-05-14 13:02 ` Peter Zijlstra
2020-05-14 22:51 ` Vineeth Remanan Pillai
2020-05-15 10:38 ` Peter Zijlstra
2020-05-15 10:43 ` Peter Zijlstra
2020-05-15 14:24 ` Vineeth Remanan Pillai
2020-05-16 3:42 ` Aaron Lu
2020-05-22 9:40 ` Aaron Lu [this message]
2020-06-08 1:41 ` Ning, Hongyu
2020-03-04 17:00 ` [RFC PATCH 10/13] sched: Trivial forced-newidle balancer vpillai
2020-03-04 17:00 ` [RFC PATCH 11/13] sched: migration changes for core scheduling vpillai
2020-06-12 13:21 ` Joel Fernandes
2020-06-12 21:32 ` Vineeth Remanan Pillai
2020-06-13 2:25 ` Joel Fernandes
2020-06-13 18:59 ` Vineeth Remanan Pillai
2020-06-15 2:05 ` Li, Aubrey
2020-03-04 17:00 ` [RFC PATCH 12/13] sched: cgroup tagging interface " vpillai
2020-06-26 15:06 ` Vineeth Remanan Pillai
2020-03-04 17:00 ` [RFC PATCH 13/13] sched: Debug bits vpillai
2020-03-04 17:36 ` [RFC PATCH 00/13] Core scheduling v5 Tim Chen
2020-03-04 17:42 ` Vineeth Remanan Pillai
2020-04-14 14:21 ` Peter Zijlstra
2020-04-15 16:32 ` Joel Fernandes
2020-04-17 11:12 ` Peter Zijlstra
2020-04-17 12:35 ` Alexander Graf
2020-04-17 13:08 ` Peter Zijlstra
2020-04-18 2:25 ` Joel Fernandes
2020-05-09 14:35 ` Dario Faggioli
[not found] ` <38805656-2e2f-222a-c083-692f4b113313@linux.intel.com>
2020-05-09 3:39 ` Ning, Hongyu
2020-05-14 20:51 ` FW: " Gruza, Agata
2020-05-10 23:46 ` [PATCH RFC] Add support for core-wide protection of IRQ and softirq Joel Fernandes (Google)
2020-05-11 13:49 ` Peter Zijlstra
2020-05-11 14:54 ` Joel Fernandes
2020-05-20 22:26 ` [PATCH RFC] sched: Add a per-thread core scheduling interface Joel Fernandes (Google)
2020-05-21 4:09 ` [PATCH RFC] sched: Add a per-thread core scheduling interface(Internet mail) benbjiang(蒋彪)
2020-05-21 13:49 ` Joel Fernandes
2020-05-21 8:51 ` [PATCH RFC] sched: Add a per-thread core scheduling interface Peter Zijlstra
2020-05-21 13:47 ` Joel Fernandes
2020-05-21 20:20 ` Vineeth Remanan Pillai
2020-05-22 12:59 ` Peter Zijlstra
2020-05-22 21:35 ` Joel Fernandes
2020-05-24 14:00 ` Phil Auld
2020-05-28 14:51 ` Joel Fernandes
2020-05-28 17:01 ` Peter Zijlstra
2020-05-28 18:17 ` Phil Auld
2020-05-28 18:34 ` Phil Auld
2020-05-28 18:23 ` Joel Fernandes
2020-05-21 18:31 ` Linus Torvalds
2020-05-21 20:40 ` Joel Fernandes
2020-05-21 21:58 ` Jesse Barnes
2020-05-22 16:33 ` Linus Torvalds
2020-05-20 22:37 ` [PATCH RFC v2] Add support for core-wide protection of IRQ and softirq Joel Fernandes (Google)
2020-05-20 22:48 ` [PATCH RFC] sched: Use sched-RCU in core-scheduling balancing logic Joel Fernandes (Google)
2020-05-21 22:52 ` Paul E. McKenney
2020-05-22 1:26 ` Joel Fernandes
2020-06-25 20:12 ` [RFC PATCH 00/13] Core scheduling v5 Vineeth Remanan Pillai
2020-06-26 1:47 ` Joel Fernandes
2020-06-26 14:36 ` Vineeth Remanan Pillai
2020-06-26 15:10 ` Joel Fernandes
2020-06-26 15:12 ` Joel Fernandes
2020-06-27 16:21 ` Joel Fernandes
2020-06-30 14:11 ` Phil Auld
2020-06-29 12:33 ` Li, Aubrey
2020-06-29 19:41 ` Vineeth Remanan Pillai
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