This is a note to let you know that I've just added the patch titled
sched/fair: Fix effective_load() to consistently use smoothed load
to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fair-fix-effective_load-to-consistently-use-smoothed-load.patch
and it can be found in the queue-4.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7dd4912594daf769a46744848b05bd5bc6d62469 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Fri, 24 Jun 2016 15:53:54 +0200
Subject: sched/fair: Fix effective_load() to consistently use smoothed load
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 7dd4912594daf769a46744848b05bd5bc6d62469 upstream.
Starting with the following commit:
fde7d22e01aa ("sched/fair: Fix overly small weight for interactive group entities")
calc_tg_weight() doesn't compute the right value as expected by effective_load().
The difference is in the 'correction' term. In order to ensure \Sum
rw_j >= rw_i we cannot use tg->load_avg directly, since that might be
lagging a correction on the current cfs_rq->avg.load_avg value.
Therefore we use tg->load_avg - cfs_rq->tg_load_avg_contrib +
cfs_rq->avg.load_avg.
Now, per the referenced commit, calc_tg_weight() doesn't use
cfs_rq->avg.load_avg, as is later used in @w, but uses
cfs_rq->load.weight instead.
So stop using calc_tg_weight() and do it explicitly.
The effects of this bug are wake_affine() making randomly
poor choices in cgroup-intense workloads.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: fde7d22e01aa ("sched/fair: Fix overly small weight for interactive group entities")
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/fair.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -687,8 +687,6 @@ void init_entity_runnable_average(struct
/* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
}
-static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq);
-static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq);
#else
void init_entity_runnable_average(struct sched_entity *se)
{
@@ -4822,19 +4820,24 @@ static long effective_load(struct task_g
return wl;
for_each_sched_entity(se) {
- long w, W;
+ struct cfs_rq *cfs_rq = se->my_q;
+ long W, w = cfs_rq_load_avg(cfs_rq);
- tg = se->my_q->tg;
+ tg = cfs_rq->tg;
/*
* W = @wg + \Sum rw_j
*/
- W = wg + calc_tg_weight(tg, se->my_q);
+ W = wg + atomic_long_read(&tg->load_avg);
+
+ /* Ensure \Sum rw_j >= rw_i */
+ W -= cfs_rq->tg_load_avg_contrib;
+ W += w;
/*
* w = rw_i + @wl
*/
- w = cfs_rq_load_avg(se->my_q) + wl;
+ w += wl;
/*
* wl = S * s'_i; see (2)
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-4.6/x86-quirks-apply-nvidia_bugs-quirk-only-on-root-bus.patch
queue-4.6/x86-quirks-add-early-quirk-to-reset-apple-airport-card.patch
queue-4.6/sched-fair-fix-effective_load-to-consistently-use-smoothed-load.patch
queue-4.6/sched-debug-fix-deadlock-when-enabling-sched-events.patch
queue-4.6/x86-quirks-reintroduce-scanning-of-secondary-buses.patch
queue-4.6/kernel-sysrq-watchdog-sched-core-reset-watchdog-on-all-cpus-while-processing-sysrq-w.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html