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From: luca abeni <luca.abeni@santannapisa.it>
To: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Juri Lelli <juri.lelli@gmail.com>,
	syzbot <syzbot+385468161961cee80c31@syzkaller.appspotmail.com>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	LKML <linux-kernel@vger.kernel.org>,
	mingo@redhat.com, nstange@suse.de,
	syzkaller-bugs@googlegroups.com, henrik@austad.us,
	Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
	Claudio Scordino <claudio@evidence.eu.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: INFO: rcu detected stall in do_idle
Date: Thu, 18 Oct 2018 12:38:05 +0200	[thread overview]
Message-ID: <20181018123805.0f4cadd0@luca64> (raw)
In-Reply-To: <20181018101008.GB21611@localhost.localdomain>

Hi Juri,

On Thu, 18 Oct 2018 12:10:08 +0200
Juri Lelli <juri.lelli@redhat.com> wrote:
[...]
> > Yes, a HZ related limit sounds like something we'd want. But if
> > we're going to do a minimum sysctl, we should also consider adding
> > a maximum, if you set a massive period/deadline, you can, even with
> > a relatively low u, incur significant delays.
> > 
> > And do we want to put the limit on runtime or on period ?
> > 
> > That is, something like:
> > 
> >   TICK_NSEC/2 < period < 10*TICK_NSEC
> > 
> > and/or
> > 
> >   TICK_NSEC/2 < runtime < 10*TICK_NSEC
> > 
> > Hmm, for HZ=1000 that ends up with a max period of 10ms, that's far
> > too low, 24Hz needs ~41ms. We can of course also limit the runtime
> > by capping u for users (as we should anyway).  
> 
> I also thought of TICK_NSEC/2 as a reasonably safe lower limit

I tend to think that something larger than "2" should be used (maybe
10? I mean: even if HZ = 100, it might make sense to allow a runtime
equal to 1ms...)


> that will implicitly limit period as well since
> 
>    runtime <= deadline <= period

I agree that if we end up with TICK_NSEC/2 for the runtime limit then
explicitly enforcing a minimum period is not needed.



> Not sure about the upper limit, though. Lower limit is something
> related to the inherent granularity of the platform/config, upper
> limit is more to do with highest prio stuff with huge period delaying
> everything else; doesn't seem to be related to HZ?

I agree


			Luca

  reply	other threads:[~2018-10-18 10:38 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-13  7:31 INFO: rcu detected stall in do_idle syzbot
2018-10-16 13:24 ` Thomas Gleixner
2018-10-16 14:03   ` Peter Zijlstra
2018-10-16 14:41     ` Juri Lelli
2018-10-16 14:45       ` Thomas Gleixner
2018-10-16 15:36         ` Juri Lelli
2018-10-18  8:28           ` Juri Lelli
2018-10-18  9:48             ` Peter Zijlstra
2018-10-18 10:10               ` Juri Lelli
2018-10-18 10:38                 ` luca abeni [this message]
2018-10-18 10:33               ` luca abeni
2018-10-19 13:14                 ` Peter Zijlstra
2018-10-18 10:23             ` luca abeni
2018-10-18 10:47               ` Juri Lelli
2018-10-18 11:08                 ` luca abeni
2018-10-18 12:21                   ` Juri Lelli
2018-10-18 12:36                     ` luca abeni
2018-10-19 11:39                   ` Peter Zijlstra
2018-10-19 20:50                     ` luca abeni
2018-10-24 12:03                       ` Juri Lelli
2018-10-27 11:16                         ` Dmitry Vyukov
2018-10-28  8:33                           ` Juri Lelli
2018-10-30 10:45                         ` Peter Zijlstra
2018-10-30 11:08                           ` luca abeni
2018-10-31 16:18                             ` Daniel Bristot de Oliveira
2018-10-31 16:40                               ` Juri Lelli
2018-10-31 17:39                                 ` Peter Zijlstra
2018-10-31 17:58                                 ` Daniel Bristot de Oliveira
2018-11-01  5:55                                   ` Juri Lelli
2018-11-02 10:00                                     ` Daniel Bristot de Oliveira
2018-11-05 10:55                                       ` Juri Lelli
2018-11-07 10:12                                         ` Daniel Bristot de Oliveira
2018-10-31 17:38                               ` Peter Zijlstra
2018-10-30 11:12                           ` Juri Lelli
2018-11-06 11:44                             ` Juri Lelli
2021-10-27  0:59 Hao Sun

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