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@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
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
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