lkml.org 
[lkml]   [2020]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] sched/fair: improve spreading of utilization
Date

On Thu, Mar 12 2020, Vincent Guittot wrote:
> kernel/sched/fair.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3c8a379c357e..97a0307312d9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9025,6 +9025,14 @@ static struct rq *find_busiest_queue(struct lb_env *env,
> case migrate_util:
> util = cpu_util(cpu_of(rq));
>
> + /*
> + * Don't try to pull utilization from a CPU with one
> + * running task. Whatever its utilization, we will fail
> + * detach the task.
> + */
> + if (nr_running <= 1)
> + continue;
> +

Doesn't this break misfit? If the busiest group is group_misfit_task, it
is totally valid for the runqueues to have a single running task -
that's the CPU-bound task we want to upmigrate.

If the busiest rq has only a single running task, we'll skip the
detach_tasks() block and go straight to the active balance bits.
Misfit balancing totally relies on this, and IMO ASYM_PACKING does
too. Looking at voluntary_active_balance(), it seems your change also
goes against the one added by
1aaf90a4b88a ("sched: Move CFS tasks to CPUs with higher capacity")

The bandaid here would be gate this 'continue' with checks against the
busiest_group_type, but that's only a loose link wrt
voluntary_active_balance().

> if (busiest_util < util) {
> busiest_util = util;
> busiest = rq;

\
 
 \ /
  Last update: 2020-03-13 12:00    [W:0.082 / U:1.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site