From: Julien Desfossez <jdesfossez@digitalocean.com>
To: Subhra Mazumdar <subhra.mazumdar@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, tglx@linutronix.de, pjt@google.com,
tim.c.chen@linux.intel.com, torvalds@linux-foundation.org,
linux-kernel@vger.kernel.org, fweisbec@gmail.com,
keescook@chromium.org, kerrnel@google.com,
Vineeth Pillai <vpillai@digitalocean.com>,
Nishanth Aravamudan <naravamudan@digitalocean.com>
Subject: Re: [RFC][PATCH 03/16] sched: Wrap rq::lock access
Date: Wed, 3 Apr 2019 16:16:34 -0400 [thread overview]
Message-ID: <20190403201634.GA4192@sinkpad> (raw)
In-Reply-To: <cd11cde9-4aed-b02f-cae5-170bb6fa686b@oracle.com>
> >>>Is the core wide lock primarily responsible for the regression? I ran
> >>>upto patch
> >>>12 which also has the core wide lock for tagged cgroups and also calls
> >>>newidle_balance() from pick_next_task(). I don't see any regression.
> >>>Of
> >>>course
> >>>the core sched version of pick_next_task() may be doing more but
> >>>comparing with
> >>>the __pick_next_task() it doesn't look too horrible.
> >>On further testing and investigation, we also agree that spinlock
> >>contention
> >>is not the major cause for the regression, but we feel that it should be
> >>one
> >>of the major contributing factors to this performance loss.
> >>
> >>
> >I finally did some code bisection and found the following lines are
> >basically responsible for the regression. Commenting them out I don't see
> >the regressions. Can you confirm? I am yet to figure if this is needed for
> >the correctness of core scheduling and if so can we do this better?
> >
> >-------->8-------------
> >
> >diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >index fe3918c..3b3388a 100644
> >--- a/kernel/sched/core.c
> >+++ b/kernel/sched/core.c
> >@@ -3741,8 +3741,8 @@ pick_next_task(struct rq *rq, struct task_struct
> >*prev, struct rq_flags *rf)
> > * If there weren't no cookies; we don't
> >need
> > * to bother with the other siblings.
> >*/
> >- if (i == cpu && !rq->core->core_cookie)
> >- goto next_class;
> >+ //if (i == cpu && !rq->core->core_cookie)
> >+ //goto next_class;
> >
> >continue;
> > }
> AFAICT this condition is not needed for correctness as cookie matching will
> sill be enforced. Peter any thoughts? I get the following numbers with 1 DB
> and 2 DB instance.
>
> 1 DB instance
> users baseline %idle core_sched %idle
> 16 1 84 -5.5% 84
> 24 1 76 -5% 76
> 32 1 69 -0.45% 69
>
> 2 DB instance
> users baseline %idle core_sched %idle
> 16 1 66 -23.8% 69
> 24 1 54 -3.1% 57
> 32 1 42 -21.1% 48
We tried to comment those lines and it doesn’t seem to get rid of the
performance regression we are seeing.
Can you elaborate a bit more about the test you are performing, what kind of
resources it uses ?
Can you also try to replicate our test and see if you see the same problem ?
cgcreate -g cpu,cpuset:set1
cat /sys/devices/system/cpu/cpu{0,2,4,6}/topology/thread_siblings_list
0,36
2,38
4,40
6,42
echo "0,2,4,6,36,38,40,42" | sudo tee /sys/fs/cgroup/cpuset/set1/cpuset.cpus
echo 0 | sudo tee /sys/fs/cgroup/cpuset/set1/cpuset.mems
echo 1 | sudo tee /sys/fs/cgroup/cpu,cpuacct/set1/cpu.tag
sysbench --test=fileio prepare
cgexec -g cpu,cpuset:set1 sysbench --threads=4 --test=fileio \
--file-test-mode=seqwr run
The reason we create a cpuset is to narrow down the investigation to just 4
cores on a highly powerful machine. It might not be needed if testing on a
smaller machine.
Julien
next prev parent reply other threads:[~2019-04-03 20:16 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-18 16:56 [RFC][PATCH 00/16] sched: Core scheduling Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 01/16] stop_machine: Fix stop_cpus_in_progress ordering Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 02/16] sched: Fix kerneldoc comment for ia64_set_curr_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 03/16] sched: Wrap rq::lock access Peter Zijlstra
2019-02-19 16:13 ` Phil Auld
2019-02-19 16:22 ` Peter Zijlstra
2019-02-19 16:37 ` Phil Auld
2019-03-18 15:41 ` Julien Desfossez
2019-03-20 2:29 ` Subhra Mazumdar
2019-03-21 21:20 ` Julien Desfossez
2019-03-22 13:34 ` Peter Zijlstra
2019-03-22 20:59 ` Julien Desfossez
2019-03-23 0:06 ` Subhra Mazumdar
2019-03-27 1:02 ` Subhra Mazumdar
2019-03-29 13:35 ` Julien Desfossez
2019-03-29 22:23 ` Subhra Mazumdar
2019-04-01 21:35 ` Subhra Mazumdar
2019-04-03 20:16 ` Julien Desfossez [this message]
2019-04-05 1:30 ` Subhra Mazumdar
2019-04-02 7:42 ` Peter Zijlstra
2019-03-22 23:28 ` Tim Chen
2019-03-22 23:44 ` Tim Chen
2019-02-18 16:56 ` [RFC][PATCH 04/16] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 05/16] sched: Add task_struct pointer to sched_class::set_curr_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 06/16] sched/fair: Export newidle_balance() Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 07/16] sched: Allow put_prev_task() to drop rq->lock Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 08/16] sched: Rework pick_next_task() slow-path Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 09/16] sched: Introduce sched_class::pick_task() Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 10/16] sched: Core-wide rq->lock Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 11/16] sched: Basic tracking of matching tasks Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 12/16] sched: A quick and dirty cgroup tagging interface Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 13/16] sched: Add core wide task selection and scheduling Peter Zijlstra
[not found] ` <20190402064612.GA46500@aaronlu>
2019-04-02 8:28 ` Peter Zijlstra
2019-04-02 13:20 ` Aaron Lu
2019-04-05 14:55 ` Aaron Lu
2019-04-09 18:09 ` Tim Chen
2019-04-10 4:36 ` Aaron Lu
2019-04-10 14:18 ` Aubrey Li
2019-04-11 2:11 ` Aaron Lu
2019-04-10 14:44 ` Peter Zijlstra
2019-04-11 3:05 ` Aaron Lu
2019-04-11 9:19 ` Peter Zijlstra
2019-04-10 8:06 ` Peter Zijlstra
2019-04-10 19:58 ` Vineeth Remanan Pillai
2019-04-15 16:59 ` Julien Desfossez
2019-04-16 13:43 ` Aaron Lu
2019-04-09 18:38 ` Julien Desfossez
2019-04-10 15:01 ` Peter Zijlstra
2019-04-11 0:11 ` Subhra Mazumdar
2019-04-19 8:40 ` Ingo Molnar
2019-04-19 23:16 ` Subhra Mazumdar
2019-02-18 16:56 ` [RFC][PATCH 14/16] sched/fair: Add a few assertions Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 15/16] sched: Trivial forced-newidle balancer Peter Zijlstra
2019-02-21 16:19 ` Valentin Schneider
2019-02-21 16:41 ` Peter Zijlstra
2019-02-21 16:47 ` Peter Zijlstra
2019-02-21 18:28 ` Valentin Schneider
2019-04-04 8:31 ` Aubrey Li
2019-04-06 1:36 ` Aubrey Li
2019-02-18 16:56 ` [RFC][PATCH 16/16] sched: Debug bits Peter Zijlstra
2019-02-18 17:49 ` [RFC][PATCH 00/16] sched: Core scheduling Linus Torvalds
2019-02-18 20:40 ` Peter Zijlstra
2019-02-19 0:29 ` Linus Torvalds
2019-02-19 15:15 ` Ingo Molnar
2019-02-22 12:17 ` Paolo Bonzini
2019-02-22 14:20 ` Peter Zijlstra
2019-02-22 19:26 ` Tim Chen
2019-02-26 8:26 ` Aubrey Li
2019-02-27 7:54 ` Aubrey Li
2019-02-21 2:53 ` Subhra Mazumdar
2019-02-21 14:03 ` Peter Zijlstra
2019-02-21 18:44 ` Subhra Mazumdar
2019-02-22 0:34 ` Subhra Mazumdar
2019-02-22 12:45 ` Mel Gorman
2019-02-22 16:10 ` Mel Gorman
2019-03-08 19:44 ` Subhra Mazumdar
2019-03-11 4:23 ` Aubrey Li
2019-03-11 18:34 ` Subhra Mazumdar
2019-03-11 23:33 ` Subhra Mazumdar
2019-03-12 0:20 ` Greg Kerr
2019-03-12 0:47 ` Subhra Mazumdar
2019-03-12 7:33 ` Aaron Lu
2019-03-12 7:45 ` Aubrey Li
2019-03-13 5:55 ` Aubrey Li
2019-03-14 0:35 ` Tim Chen
2019-03-14 5:30 ` Aubrey Li
2019-03-14 6:07 ` Li, Aubrey
2019-03-18 6:56 ` Aubrey Li
2019-03-12 19:07 ` Pawan Gupta
2019-03-26 7:32 ` Aaron Lu
2019-03-26 7:56 ` Aaron Lu
2019-02-19 22:07 ` Greg Kerr
2019-02-20 9:42 ` Peter Zijlstra
2019-02-20 18:33 ` Greg Kerr
2019-02-22 14:10 ` Peter Zijlstra
2019-03-07 22:06 ` Paolo Bonzini
2019-02-20 18:43 ` Subhra Mazumdar
2019-03-01 2:54 ` Subhra Mazumdar
2019-03-14 15:28 ` Julien Desfossez
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