linux-kernel - Re: [RFC PATCH] tick/sched: update full_nohz status after SCHED dep is cleared

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Date:   Thu, 21 May 2020 02:44:44 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     fweisbec@...il.com, tglx@...utronix.de, mingo@...nel.org,
        linux-rt-users@...r.kernel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] tick/sched: update full_nohz status after SCHED dep
 is cleared

On Wed, May 20, 2020 at 08:47:10PM +0200, Juri Lelli wrote:
> On 20/05/20 19:02, Frederic Weisbecker wrote:
> > On Wed, May 20, 2020 at 06:49:25PM +0200, Juri Lelli wrote:
> > > On 20/05/20 18:24, Frederic Weisbecker wrote:
> > > 
> > > Hummm, so I enabled 'timer:*', anything else you think I should be
> > > looking at?
> > 
> > Are you sure you also enabled timer_expire_entry?
> > Because:
> 
> I run with
> 
> trace-cmd record -e sched_switch -e sched_wakeup -e sched_migrate_task \
> -e 'timer:*' -e 'irq_vectors:*' -e 'irq:softirq*' \
> -e 'irq:irq_handler*' taskset --cpu-list 4-35 ./sysjitter/sysjitter \
> --runtime 10 200
> 
> And
> 
> $ grep ' timer_expire_entry:' trace.txt | wc -l
> 1173
> 
> seems to confirm that the event was indeed enabled, e.g.
> 
> ksoftirqd/11-100   [011]   159.270023: timer_expire_entry:   timer=0xffff9807df8a5a60 function=delayed_work_timer_fn now=4294826418 baseclk=4294825984

That's interesting! I'll see if I can reproduce that with threaded irqs. If not we'll
have to investigate on your machine. We really don't want to trigger timer softirqs
when it's not necessary.