* sched/fair: Fix fixed point arithmetic width for shares and effective load
@ 2017-01-07 20:38 Samuel Thibault
2017-01-08 11:29 ` Greg KH
0 siblings, 1 reply; 6+ messages in thread
From: Samuel Thibault @ 2017-01-07 20:38 UTC (permalink / raw)
To: stable, Greg KH
Cc: Dietmar Eggemann, Peter Zijlstra, Mike Galbraith, Thomas Gleixner
Hello,
Please backport
commit ab522e33f91799661aad47bebb691f241a9f6bb8
('sched/fair: Fix fixed point arithmetic width for shares and effective load')
to 4.8.
It was apparently not backported as of 4.8.16, while it fixes a huge
performance regression in our tests, see the graphs between 19320.5 and
19451.5 on
http://starpu.gforge.inria.fr/testing/trunk/benchmarks/tasks_size_overhead_total_lws-200.png
which happened to be using a kernel without this fix.
FTR, here is the patch again.
Samuel
commit ab522e33f91799661aad47bebb691f241a9f6bb8
Author: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Mon Aug 22 15:00:41 2016 +0100
sched/fair: Fix fixed point arithmetic width for shares and effective load
Since commit:
2159197d6677 ("sched/core: Enable increased load resolution on 64-bit kernels")
we now have two different fixed point units for load:
- 'shares' in calc_cfs_shares() has 20 bit fixed point unit on 64-bit
kernels. Therefore use scale_load() on MIN_SHARES.
- 'wl' in effective_load() has 10 bit fixed point unit. Therefore use
scale_load_down() on tg->shares which has 20 bit fixed point unit on
64-bit kernels.
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8fb4d19..786ef94 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5017,9 +5017,9 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
* wl = S * s'_i; see (2)
*/
if (W > 0 && w < W)
- wl = (w * (long)tg->shares) / W;
+ wl = (w * (long)scale_load_down(tg->shares)) / W;
else
- wl = tg->shares;
+ wl = scale_load_down(tg->shares);
/*
* Per the above, wl is the new se->load.weight value; since
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: sched/fair: Fix fixed point arithmetic width for shares and effective load
2017-01-07 20:38 sched/fair: Fix fixed point arithmetic width for shares and effective load Samuel Thibault
@ 2017-01-08 11:29 ` Greg KH
2017-01-08 11:32 ` Samuel Thibault
0 siblings, 1 reply; 6+ messages in thread
From: Greg KH @ 2017-01-08 11:29 UTC (permalink / raw)
To: Samuel Thibault, stable, Dietmar Eggemann, Peter Zijlstra,
Mike Galbraith, Thomas Gleixner
On Sat, Jan 07, 2017 at 09:38:36PM +0100, Samuel Thibault wrote:
> Hello,
>
> Please backport
> commit ab522e33f91799661aad47bebb691f241a9f6bb8
> ('sched/fair: Fix fixed point arithmetic width for shares and effective load')
> to 4.8.
As 4.8-stable is about to go end-of-life on Monday (tomorrow), can't you
just use 4.9 instead?
> It was apparently not backported as of 4.8.16, while it fixes a huge
> performance regression in our tests, see the graphs between 19320.5 and
> 19451.5 on
>
> http://starpu.gforge.inria.fr/testing/trunk/benchmarks/tasks_size_overhead_total_lws-200.png
>
> which happened to be using a kernel without this fix.
>
> FTR, here is the patch again.
>
> Samuel
>
> commit ab522e33f91799661aad47bebb691f241a9f6bb8
> Author: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Date: Mon Aug 22 15:00:41 2016 +0100
>
> sched/fair: Fix fixed point arithmetic width for shares and effective load
>
> Since commit:
>
> 2159197d6677 ("sched/core: Enable increased load resolution on 64-bit kernels")
>
> we now have two different fixed point units for load:
>
> - 'shares' in calc_cfs_shares() has 20 bit fixed point unit on 64-bit
> kernels. Therefore use scale_load() on MIN_SHARES.
>
> - 'wl' in effective_load() has 10 bit fixed point unit. Therefore use
> scale_load_down() on tg->shares which has 20 bit fixed point unit on
> 64-bit kernels.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Mike Galbraith <efault@gmx.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@arm.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
I would need an ack from the developers of the patch before I could take
this into a stable kernel, but again, it's a bit late for 4.8, so I
don't think we should worry about it anymore, do you?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: sched/fair: Fix fixed point arithmetic width for shares and effective load
2017-01-08 11:29 ` Greg KH
@ 2017-01-08 11:32 ` Samuel Thibault
2017-01-08 12:51 ` Greg KH
0 siblings, 1 reply; 6+ messages in thread
From: Samuel Thibault @ 2017-01-08 11:32 UTC (permalink / raw)
To: Greg KH
Cc: stable, Dietmar Eggemann, Peter Zijlstra, Mike Galbraith,
Thomas Gleixner
Greg KH, on Sun 08 Jan 2017 12:29:18 +0100, wrote:
> On Sat, Jan 07, 2017 at 09:38:36PM +0100, Samuel Thibault wrote:
> > Please backport
> > commit ab522e33f91799661aad47bebb691f241a9f6bb8
> > ('sched/fair: Fix fixed point arithmetic width for shares and effective load')
> > to 4.8.
>
> As 4.8-stable is about to go end-of-life on Monday (tomorrow),
Ah Ok.
> can't you just use 4.9 instead?
I can, but we have users which use various distributions. But since 4.8
goes end-of-life, I guess no distribution will use it and the problem is
indeed moot.
Thanks,
Samuel
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: sched/fair: Fix fixed point arithmetic width for shares and effective load
2017-01-08 11:32 ` Samuel Thibault
@ 2017-01-08 12:51 ` Greg KH
2017-01-08 12:52 ` Samuel Thibault
0 siblings, 1 reply; 6+ messages in thread
From: Greg KH @ 2017-01-08 12:51 UTC (permalink / raw)
To: Samuel Thibault, stable, Dietmar Eggemann, Peter Zijlstra,
Mike Galbraith, Thomas Gleixner
On Sun, Jan 08, 2017 at 12:32:48PM +0100, Samuel Thibault wrote:
> Greg KH, on Sun 08 Jan 2017 12:29:18 +0100, wrote:
> > On Sat, Jan 07, 2017 at 09:38:36PM +0100, Samuel Thibault wrote:
> > > Please backport
> > > commit ab522e33f91799661aad47bebb691f241a9f6bb8
> > > ('sched/fair: Fix fixed point arithmetic width for shares and effective load')
> > > to 4.8.
> >
> > As 4.8-stable is about to go end-of-life on Monday (tomorrow),
>
> Ah Ok.
>
> > can't you just use 4.9 instead?
>
> I can, but we have users which use various distributions.
What distros are stuck on 4.8 that are not going to be moving to 4.9
within a week or so that you care about?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: sched/fair: Fix fixed point arithmetic width for shares and effective load
2017-01-08 12:51 ` Greg KH
@ 2017-01-08 12:52 ` Samuel Thibault
0 siblings, 0 replies; 6+ messages in thread
From: Samuel Thibault @ 2017-01-08 12:52 UTC (permalink / raw)
To: Greg KH
Cc: stable, Dietmar Eggemann, Peter Zijlstra, Mike Galbraith,
Thomas Gleixner
Greg KH, on Sun 08 Jan 2017 13:51:22 +0100, wrote:
> On Sun, Jan 08, 2017 at 12:32:48PM +0100, Samuel Thibault wrote:
> > Greg KH, on Sun 08 Jan 2017 12:29:18 +0100, wrote:
> > > On Sat, Jan 07, 2017 at 09:38:36PM +0100, Samuel Thibault wrote:
> > > > Please backport
> > > > commit ab522e33f91799661aad47bebb691f241a9f6bb8
> > > > ('sched/fair: Fix fixed point arithmetic width for shares and effective load')
> > > > to 4.8.
> > >
> > > As 4.8-stable is about to go end-of-life on Monday (tomorrow),
> >
> > Ah Ok.
> >
> > > can't you just use 4.9 instead?
> >
> > I can, but we have users which use various distributions.
>
> What distros are stuck on 4.8 that are not going to be moving to 4.9
> within a week or so that you care about?
I don't know, but there are so many of them that you never know :)
But given 4.8 is end-of-line, I now guess there won't be any.
Samuel
^ permalink raw reply [flat|nested] 6+ messages in thread
* sched/fair: Fix fixed point arithmetic width for shares and effective load
@ 2016-12-19 20:27 Samuel Thibault
0 siblings, 0 replies; 6+ messages in thread
From: Samuel Thibault @ 2016-12-19 20:27 UTC (permalink / raw)
To: stable; +Cc: Dietmar Eggemann, Peter Zijlstra, Mike Galbraith, Thomas Gleixner
Hello,
Please backport
commit ab522e33f91799661aad47bebb691f241a9f6bb8
('sched/fair: Fix fixed point arithmetic width for shares and effective load')
to 4.7 and 4.8.
It was apparently not backported as of 4.7.10 and 4.8.15, while it fixes
a huge performance regression in our tests, see the graphs between
19320.5 and 19451.5 on
http://starpu.gforge.inria.fr/testing/trunk/benchmarks/tasks_size_overhead_total_lws-200.png
which happened to be using a kernel without this fix.
FTR, here is the patch again.
Samuel
commit ab522e33f91799661aad47bebb691f241a9f6bb8
Author: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Mon Aug 22 15:00:41 2016 +0100
sched/fair: Fix fixed point arithmetic width for shares and effective load
Since commit:
2159197d6677 ("sched/core: Enable increased load resolution on 64-bit kernels")
we now have two different fixed point units for load:
- 'shares' in calc_cfs_shares() has 20 bit fixed point unit on 64-bit
kernels. Therefore use scale_load() on MIN_SHARES.
- 'wl' in effective_load() has 10 bit fixed point unit. Therefore use
scale_load_down() on tg->shares which has 20 bit fixed point unit on
64-bit kernels.
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8fb4d19..786ef94 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5017,9 +5017,9 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
* wl = S * s'_i; see (2)
*/
if (W > 0 && w < W)
- wl = (w * (long)tg->shares) / W;
+ wl = (w * (long)scale_load_down(tg->shares)) / W;
else
- wl = tg->shares;
+ wl = scale_load_down(tg->shares);
/*
* Per the above, wl is the new se->load.weight value; since
^ permalink raw reply related [flat|nested] 6+ messages in thread
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2017-01-07 20:38 sched/fair: Fix fixed point arithmetic width for shares and effective load Samuel Thibault
2017-01-08 11:29 ` Greg KH
2017-01-08 11:32 ` Samuel Thibault
2017-01-08 12:51 ` Greg KH
2017-01-08 12:52 ` Samuel Thibault
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2016-12-19 20:27 Samuel Thibault
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