From: Quentin Perret <quentin.perret@arm.com>
To: Luca Abeni <luca.abeni@santannapisa.it>
Cc: linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J . Wysocki" <rafael@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
"Paul E . McKenney" <paulmck@linux.ibm.com>,
Joel Fernandes <joel@joelfernandes.org>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>
Subject: Re: [RFC PATCH 6/6] sched/dl: Try not to select a too fast core
Date: Tue, 7 May 2019 16:57:34 +0100 [thread overview]
Message-ID: <20190507155732.7ravrnld54rb6k5a@queper01-lin> (raw)
In-Reply-To: <20190506044836.2914-7-luca.abeni@santannapisa.it>
On Monday 06 May 2019 at 06:48:36 (+0200), Luca Abeni wrote:
> From: luca abeni <luca.abeni@santannapisa.it>
>
> When a task can fit on multiple CPU cores, try to select the slowest
> core that is able to properly serve the task. This avoids useless
> future migrations, leaving the "fast cores" idle for more heavyweight
> tasks.
But only if the _current_ capacity of big CPUs (at the current freq) is
higher than the current capacity of the littles, is that right ? So we
don't really have a guarantee to pack small tasks on little cores ...
What is the rationale for looking at the current freq in dl_task_fit() ?
Energy reasons ? If so, I'd argue you should look at the energy model to
break the tie between CPU candidates ... ;)
And in the mean time, you could just look at arch_scale_cpu_capacity()
to check if a task fits ?
> Signed-off-by: luca abeni <luca.abeni@santannapisa.it>
> ---
> kernel/sched/cpudeadline.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 2a4ac7b529b7..897ed71af515 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -143,17 +143,24 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
> struct cpumask *later_mask)
> {
> const struct sched_dl_entity *dl_se = &p->dl;
> + struct cpumask tmp_mask;
Hmm, these can get pretty big, so not sure about having one on the stack ...
>
> if (later_mask &&
> - cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
> + cpumask_and(&tmp_mask, cp->free_cpus, &p->cpus_allowed)) {
> int cpu, max_cpu = -1;
> - u64 max_cap = 0;
> + u64 max_cap = 0, min_cap = SCHED_CAPACITY_SCALE * SCHED_CAPACITY_SCALE;
>
> - for_each_cpu(cpu, later_mask) {
> + cpumask_clear(later_mask);
> + for_each_cpu(cpu, &tmp_mask) {
> u64 cap;
>
> - if (!dl_task_fit(&p->dl, cpu, &cap))
> - cpumask_clear_cpu(cpu, later_mask);
> + if (dl_task_fit(&p->dl, cpu, &cap) && (cap <= min_cap)) {
> + if (cap < min_cap) {
> + min_cap = cap;
> + cpumask_clear(later_mask);
> + }
> + cpumask_set_cpu(cpu, later_mask);
> + }
>
> if (cap > max_cap) {
> max_cap = cap;
> --
> 2.20.1
>
Thanks,
Quentin
next prev parent reply other threads:[~2019-05-07 15:57 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-06 4:48 [RFC PATCH 0/6] Capacity awareness for SCHED_DEADLINE Luca Abeni
2019-05-06 4:48 ` [RFC PATCH 1/6] sched/dl: Improve deadline admission control for asymmetric CPU capacities Luca Abeni
2019-05-07 13:48 ` Quentin Perret
2019-05-07 13:55 ` Vincent Guittot
2019-05-07 14:02 ` Quentin Perret
2019-05-07 14:25 ` luca abeni
2019-05-07 14:31 ` Quentin Perret
2019-05-07 14:43 ` luca abeni
2019-07-08 11:22 ` Dietmar Eggemann
2019-07-08 15:05 ` Quentin Perret
2019-06-18 16:41 ` Alessio Balsini
2019-05-06 4:48 ` [RFC PATCH 2/6] sched/dl: Capacity-aware migrations Luca Abeni
2019-05-07 13:35 ` Quentin Perret
2019-05-07 14:17 ` luca abeni
2019-05-07 15:04 ` Quentin Perret
2019-05-07 14:10 ` Quentin Perret
2019-05-07 14:41 ` luca abeni
2019-05-07 15:02 ` Quentin Perret
2019-05-08 8:04 ` Juri Lelli
2019-05-08 8:17 ` luca abeni
2019-07-04 12:05 ` Dietmar Eggemann
2019-07-08 7:41 ` luca abeni
2019-07-08 10:41 ` Dietmar Eggemann
2019-05-06 4:48 ` [RFC PATCH 3/6] sched/dl: Try better placement even for deadline tasks that do not block Luca Abeni
2019-05-07 14:13 ` Quentin Perret
2019-05-07 16:00 ` Morten Rasmussen
2019-05-08 8:01 ` Juri Lelli
2019-05-08 8:14 ` luca abeni
2019-05-08 9:22 ` Juri Lelli
2019-07-08 13:55 ` Peter Zijlstra
2019-07-09 13:24 ` luca abeni
2019-07-09 13:42 ` Peter Zijlstra
2019-07-11 11:17 ` Dietmar Eggemann
2019-07-11 12:00 ` Peter Zijlstra
2019-07-11 15:33 ` Dietmar Eggemann
2019-07-09 14:44 ` Dietmar Eggemann
2019-05-06 4:48 ` [RFC PATCH 4/6] sched/dl: Improve capacity-aware wakeup Luca Abeni
2019-05-08 9:08 ` Juri Lelli
2019-05-08 9:24 ` luca abeni
2019-05-08 12:05 ` Juri Lelli
2019-05-08 12:47 ` luca abeni
2019-05-08 13:10 ` Juri Lelli
2019-05-08 14:12 ` luca abeni
2019-05-06 4:48 ` [RFC PATCH 5/6] sched/dl: If the task does not fit anywhere, select the fastest core Luca Abeni
2019-05-06 4:48 ` [RFC PATCH 6/6] sched/dl: Try not to select a too fast core Luca Abeni
2019-05-07 15:57 ` Quentin Perret [this message]
2019-05-08 6:26 ` luca abeni
2019-05-09 13:46 ` Quentin Perret
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