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

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Message-ID: <20200629124207.GA6088@lenoir>
Date:   Mon, 29 Jun 2020 14:42:08 +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 Mon, Jun 29, 2020 at 02:36:51PM +0200, Juri Lelli wrote:
> Hi,
> 
> On 16/06/20 22:46, Frederic Weisbecker wrote:
> > On Tue, Jun 16, 2020 at 08:57:57AM +0200, Juri Lelli wrote:
> > > Sure. Let me know if you find anything.
> > 
> > I managed to reproduce. With "threadirqs" and without
> > "tsc=reliable". I see tons of spurious TIMER softirqs.
> > Investigation begins! I'll let you know.
> 
> Gentle ping. Any new findings about this issue?

Yep, I'm working on a series to reduce timer softirqs. I'm almost
done, should post it soon.

I believe you guessed right:

* Timer tick raises timer softirq
* Ksoftirqd wakes up, restarts the tick
* Timer tick raises timer softirq
* ...

Thanks.