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From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Juri Lelli <juri.lelli@redhat.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Peter Ziljstra <peterz@infradead.org>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Linux-ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP
Date: Tue, 8 Dec 2020 16:30:00 +0000	[thread overview]
Message-ID: <20201208163000.GL3371@techsingularity.net> (raw)
In-Reply-To: <CAKfTPtBGghbKimO17UTPUHQGZc=GkY849HFrkqqojirPhJKFoQ@mail.gmail.com>

On Tue, Dec 08, 2020 at 05:03:21PM +0100, Vincent Guittot wrote:
> On Tue, 8 Dec 2020 at 16:35, Mel Gorman <mgorman@techsingularity.net> wrote:
> >
> > As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
> > even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
> > check and while we are at it, exclude the cost of initialising the CPU
> > mask from the average scan cost.
> >
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > ---
> >  kernel/sched/fair.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index ac7b34e7372b..5c41875aec23 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6153,6 +6153,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> >         if (!this_sd)
> >                 return -1;
> 
> Just noticed while reviewing the patch that the above related to
> this_sd can also go under sched_feat(SIS_PROP)
> 

Technically yes but I also decided against it. It's a functional difference
depending on whether SIS_PROP is set in the highly unlikely case that
this_sd == NULL. I was also thinking in terms of what happens if SIS_PROP
was disabled and enabled while a search is in progress even if it's very
unlikely. In that case, this_sd would be uninitialised. That might be
impossible in practice depending on how static branching is implemented
but I don't think we should rely on the internals of jump labels and play
it safe. I can move it in if you feel strongly about it but I think the
disable/enable race is enough of a concern to leave it alone.

-- 
Mel Gorman
SUSE Labs

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Ziljstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Linux-ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP
Date: Tue, 8 Dec 2020 16:30:00 +0000	[thread overview]
Message-ID: <20201208163000.GL3371@techsingularity.net> (raw)
In-Reply-To: <CAKfTPtBGghbKimO17UTPUHQGZc=GkY849HFrkqqojirPhJKFoQ@mail.gmail.com>

On Tue, Dec 08, 2020 at 05:03:21PM +0100, Vincent Guittot wrote:
> On Tue, 8 Dec 2020 at 16:35, Mel Gorman <mgorman@techsingularity.net> wrote:
> >
> > As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
> > even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
> > check and while we are at it, exclude the cost of initialising the CPU
> > mask from the average scan cost.
> >
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > ---
> >  kernel/sched/fair.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index ac7b34e7372b..5c41875aec23 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6153,6 +6153,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> >         if (!this_sd)
> >                 return -1;
> 
> Just noticed while reviewing the patch that the above related to
> this_sd can also go under sched_feat(SIS_PROP)
> 

Technically yes but I also decided against it. It's a functional difference
depending on whether SIS_PROP is set in the highly unlikely case that
this_sd == NULL. I was also thinking in terms of what happens if SIS_PROP
was disabled and enabled while a search is in progress even if it's very
unlikely. In that case, this_sd would be uninitialised. That might be
impossible in practice depending on how static branching is implemented
but I don't think we should rely on the internals of jump labels and play
it safe. I can move it in if you feel strongly about it but I think the
disable/enable race is enough of a concern to leave it alone.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2020-12-08 16:31 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 15:34 [PATCH 0/4] Reduce scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-08 15:34 ` Mel Gorman
2020-12-08 15:34 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-08 15:34   ` Mel Gorman
2020-12-08 16:13   ` Vincent Guittot
2020-12-08 16:13     ` Vincent Guittot
2020-12-08 15:34 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2020-12-08 15:34   ` Mel Gorman
2020-12-08 16:03   ` Vincent Guittot
2020-12-08 16:03     ` Vincent Guittot
2020-12-08 16:30     ` Mel Gorman [this message]
2020-12-08 16:30       ` Mel Gorman
2020-12-09  5:28     ` Li, Aubrey
2020-12-09  5:28       ` Li, Aubrey
2020-12-09  9:05       ` Mel Gorman
2020-12-09  9:05         ` Mel Gorman
2020-12-09 11:07         ` Li, Aubrey
2020-12-09 11:07           ` Li, Aubrey
2020-12-09 11:33           ` Mel Gorman
2020-12-09 11:33             ` Mel Gorman
2020-12-10  5:18   ` Li, Aubrey
2020-12-10  5:18     ` Li, Aubrey
2020-12-10  9:32     ` Mel Gorman
2020-12-10  9:32       ` Mel Gorman
2020-12-08 15:35 ` [PATCH 3/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-08 15:35   ` Mel Gorman
2020-12-08 16:14   ` Vincent Guittot
2020-12-08 16:14     ` Vincent Guittot
2020-12-10  9:40     ` Vincent Guittot
2020-12-10  9:40       ` Vincent Guittot
2020-12-11  6:25   ` Hillf Danton
2020-12-11  9:02     ` Mel Gorman
2020-12-11  9:02       ` Mel Gorman
2020-12-11  9:34       ` Hillf Danton
2020-12-11  9:45         ` Mel Gorman
2020-12-11  9:45           ` Mel Gorman
2020-12-08 15:35 ` [PATCH 4/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-08 15:35   ` Mel Gorman
2020-12-08 16:15   ` Vincent Guittot
2020-12-08 16:15     ` Vincent Guittot
2020-12-09 14:37 ` [PATCH 0/4] Reduce scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-09 14:37   ` Mel Gorman
2020-12-10  8:00   ` Vincent Guittot
2020-12-10  8:00     ` Vincent Guittot
2020-12-10  9:38     ` Vincent Guittot
2020-12-10  9:38       ` Vincent Guittot
2020-12-10 11:04       ` Mel Gorman
2020-12-10 11:04         ` Mel Gorman
2020-12-11  9:51         ` Vincent Guittot
2020-12-11  9:51           ` Vincent Guittot
2020-12-11 10:23           ` Mel Gorman
2020-12-11 10:23             ` Mel Gorman
2020-12-12 10:02             ` Vincent Guittot
2020-12-12 10:02               ` Vincent Guittot
  -- strict thread matches above, loose matches on Subject: below --
2021-01-25  8:59 [PATCH v4 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-25  8:59 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2021-01-27 10:39   ` Vincent Guittot
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-27 13:52 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman

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