Re: [PATCH] sched/deadline: Fix missing clock update in migrate_task_rq_dl()

[Juri Lelli <juri.lelli@redhat.com>]

Hi,

On 04/08/21 15:59, Dietmar Eggemann wrote:
> A missing clock update is causing the following warning:
> 
> rq->clock_update_flags < RQCF_ACT_SKIP
> WARNING: CPU: 112 PID: 2041 at kernel/sched/sched.h:1453
> sub_running_bw.isra.0+0x190/0x1a0
> ...
> CPU: 112 PID: 2041 Comm: sugov:112 Tainted: G W 5.14.0-rc1 #1
> Hardware name: WIWYNN Mt.Jade Server System
> B81.030Z1.0007/Mt.Jade Motherboard, BIOS 1.6.20210526 (SCP:
> 1.06.20210526) 2021/05/26
> ...
> Call trace:
>   sub_running_bw.isra.0+0x190/0x1a0
>   migrate_task_rq_dl+0xf8/0x1e0
>   set_task_cpu+0xa8/0x1f0
>   try_to_wake_up+0x150/0x3d4
>   wake_up_q+0x64/0xc0
>   __up_write+0xd0/0x1c0
>   up_write+0x4c/0x2b0
>   cppc_set_perf+0x120/0x2d0
>   cppc_cpufreq_set_target+0xe0/0x1a4 [cppc_cpufreq]
>   __cpufreq_driver_target+0x74/0x140
>   sugov_work+0x64/0x80
>   kthread_worker_fn+0xe0/0x230
>   kthread+0x138/0x140
>   ret_from_fork+0x10/0x18
> 
> The task causing this is the `cppc_fie` DL task introduced by
> commit 1eb5dde674f5 ("cpufreq: CPPC: Add support for frequency
> invariance").
> 
> With CONFIG_ACPI_CPPC_CPUFREQ_FIE=y and schedutil cpufreq governor on
> slow-switching system (like on this Ampere Altra WIWYNN Mt. Jade Arm
> Server):
> 
> DL task `curr=sugov:112` lets `p=cppc_fie` migrate and since the latter
> is in `non_contending` state, migrate_task_rq_dl() calls
> 
>   sub_running_bw()->__sub_running_bw()->cpufreq_update_util()->
>   rq_clock()->assert_clock_updated()
> 
> on p.
> 
> Fix this by updating the clock for a non_contending task in
> migrate_task_rq_dl() before calling sub_running_bw().
> 
> Reported-by: Bruno Goncalves <bgoncalv@redhat.com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
>  kernel/sched/deadline.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index aaacd6cfd42f..4920f498492f 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1733,6 +1733,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused
>  	 */
>  	raw_spin_rq_lock(rq);
>  	if (p->dl.dl_non_contending) {
> +		update_rq_clock(rq);
>  		sub_running_bw(&p->dl, &rq->dl);
>  		p->dl.dl_non_contending = 0;
>  		/*

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Thanks!
Juri