Re: [PATCH] sched/fair: Make hrtimer callback execute in the hard interrupt context

From: Peter Zijlstra
Date: Mon Mar 06 2023 - 06:06:38 EST


On Mon, Mar 06, 2023 at 03:09:38PM +0800, Zqiang wrote:
> The scheduler related hrtimers callback will be executed in softirqd
> context for PREEMPT_RT enabled kernel, this commit therefore mark
> hrtimers as harded even on PREEMPT_RT enabled kernels, there is no
> functional change.

There very much is a functional change, also your reasoning is
non-existant.

Also:

https://lkml.kernel.org/r/Y1F5sDVGen7ZVW+U@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

> Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
> ---
> kernel/sched/fair.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c36aa54ae071..98c48d144089 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5610,7 +5610,7 @@ static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
>
> hrtimer_start(&cfs_b->slack_timer,
> ns_to_ktime(cfs_bandwidth_slack_period),
> - HRTIMER_MODE_REL);
> + HRTIMER_MODE_REL_HARD);
> }
>
> /* we know any runtime found here is valid as update_curr() precedes return */
> @@ -5813,9 +5813,9 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> cfs_b->burst = 0;
>
> INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
> - hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
> + hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
> cfs_b->period_timer.function = sched_cfs_period_timer;
> - hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> cfs_b->slack_timer.function = sched_cfs_slack_timer;
> cfs_b->slack_started = false;
> }
> @@ -5835,7 +5835,7 @@ void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
>
> cfs_b->period_active = 1;
> hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
> - hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
> + hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED_HARD);
> }
>
> static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> --
> 2.25.1
>