From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org,
josef@toxicpanda.com
Cc: torvalds@linux-foundation.org, vincent.guittot@linaro.org,
efault@gmx.de, pjt@google.com, clm@fb.com,
morten.rasmussen@arm.com, bsegall@google.com,
yuyang.du@intel.com
Subject: Re: [PATCH -v2 15/18] sched/fair: Align PELT windows between cfs_rq and its se
Date: Wed, 4 Oct 2017 20:27:01 +0100 [thread overview]
Message-ID: <fae8858f-13ce-b753-7bce-cfb6a1cba92d@arm.com> (raw)
In-Reply-To: <20170901132748.738108335@infradead.org>
On 01/09/17 14:21, Peter Zijlstra wrote:
> The PELT _sum values are a saw-tooth function, dropping on the decay
> edge and then growing back up again during the window.
>
> When these window-edges are not aligned between cfs_rq and se, we can
> have the situation where, for example, on dequeue, the se decays
> first.
>
> Its _sum values will be small(er), while the cfs_rq _sum values will
> still be on their way up. Because of this, the subtraction:
> cfs_rq->avg._sum -= se->avg._sum will result in a positive value. This
> will then, once the cfs_rq reaches an edge, translate into its _avg
> value jumping up.
>
> This is especially visible with the runnable_load bits, since they get
> added/subtracted a lot.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/fair.c | 45 +++++++++++++++++++++++++++++++--------------
> 1 file changed, 31 insertions(+), 14 deletions(-)
[...]
> @@ -3644,7 +3634,34 @@ update_cfs_rq_load_avg(u64 now, struct c
> */
> static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
> {
> + u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib;
> +
> + /*
> + * When we attach the @se to the @cfs_rq, we must align the decay
> + * window because without that, really weird and wonderful things can
> + * happen.
> + *
> + * XXX illustrate
> + */
> se->avg.last_update_time = cfs_rq->avg.last_update_time;
> + se->avg.period_contrib = cfs_rq->avg.period_contrib;
> +
> + /*
> + * Hell(o) Nasty stuff.. we need to recompute _sum based on the new
> + * period_contrib. This isn't strictly correct, but since we're
> + * entirely outside of the PELT hierarchy, nobody cares if we truncate
> + * _sum a little.
> + */
> + se->avg.util_sum = se->avg.util_avg * divider;
> +
> + se->avg.load_sum = divider;
> + if (se_weight(se)) {
> + se->avg.load_sum =
> + div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
> + }
Can scale_load_down(se->load.weight) ever become 0 here?
[...]
next prev parent reply other threads:[~2017-10-04 19:27 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-01 13:20 [PATCH -v2 00/18] sched/fair: A bit of a cgroup/PELT overhaul Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 01/18] sched/fair: Clean up calc_cfs_shares() Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 02/18] sched/fair: Add comment to calc_cfs_shares() Peter Zijlstra
2017-09-28 10:03 ` Morten Rasmussen
2017-09-29 11:35 ` Peter Zijlstra
2017-09-29 13:03 ` Morten Rasmussen
2017-09-01 13:21 ` [PATCH -v2 03/18] sched/fair: Cure calc_cfs_shares() vs reweight_entity() Peter Zijlstra
2017-09-29 9:04 ` Morten Rasmussen
2017-09-29 11:38 ` Peter Zijlstra
2017-09-29 13:00 ` Morten Rasmussen
2017-09-01 13:21 ` [PATCH -v2 04/18] sched/fair: Remove se->load.weight from se->avg.load_sum Peter Zijlstra
2017-09-29 15:26 ` Morten Rasmussen
2017-09-29 16:39 ` Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 05/18] sched/fair: Change update_load_avg() arguments Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 06/18] sched/fair: Move enqueue migrate handling Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 07/18] sched/fair: Rename {en,de}queue_entity_load_avg() Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 08/18] sched/fair: Introduce {en,de}queue_load_avg() Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 09/18] sched/fair: More accurate reweight_entity() Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 10/18] sched/fair: Use reweight_entity() for set_user_nice() Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 11/18] sched/fair: Rewrite cfs_rq->removed_*avg Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 12/18] sched/fair: Rewrite PELT migration propagation Peter Zijlstra
2017-10-09 8:08 ` Morten Rasmussen
2017-10-09 9:45 ` Peter Zijlstra
2017-10-18 12:45 ` Morten Rasmussen
2017-10-30 13:35 ` Peter Zijlstra
2017-10-09 15:03 ` Vincent Guittot
2017-10-09 15:29 ` Vincent Guittot
2017-10-10 7:29 ` Peter Zijlstra
2017-10-10 7:44 ` Vincent Guittot
2017-10-13 15:22 ` Vincent Guittot
2017-10-13 20:41 ` Peter Zijlstra
2017-10-15 12:01 ` Vincent Guittot
2017-10-16 13:55 ` Vincent Guittot
2017-10-19 15:04 ` Vincent Guittot
2017-10-30 17:20 ` Peter Zijlstra
2017-10-31 11:14 ` Vincent Guittot
2017-10-31 15:01 ` Peter Zijlstra
2017-10-31 16:38 ` Vincent Guittot
2017-11-16 14:09 ` [PATCH v3] sched: Update runnable propagation rule Vincent Guittot
2017-11-16 14:21 ` [PATCH v4] " Vincent Guittot
2017-12-06 11:40 ` Peter Zijlstra
2017-12-06 17:10 ` Ingo Molnar
2017-12-06 20:29 ` [tip:sched/core] sched/fair: Update and fix the " tip-bot for Vincent Guittot
2017-09-01 13:21 ` [PATCH -v2 13/18] sched/fair: Propagate an effective runnable_load_avg Peter Zijlstra
2017-10-02 17:46 ` Dietmar Eggemann
2017-10-03 8:50 ` Peter Zijlstra
2017-10-03 9:29 ` Dietmar Eggemann
2017-10-03 12:26 ` Dietmar Eggemann
2017-09-01 13:21 ` [PATCH -v2 14/18] sched/fair: Synchonous PELT detach on load-balance migrate Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 15/18] sched/fair: Align PELT windows between cfs_rq and its se Peter Zijlstra
2017-10-04 19:27 ` Dietmar Eggemann [this message]
2017-10-06 13:02 ` Peter Zijlstra
2017-10-09 12:15 ` Dietmar Eggemann
2017-10-09 12:19 ` Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 16/18] sched/fair: More accurate async detach Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 17/18] sched/fair: Calculate runnable_weight slightly differently Peter Zijlstra
2017-09-01 13:21 ` [PATCH -v2 18/18] sched/fair: Update calc_group_*() comments Peter Zijlstra
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