From: Peter Zijlstra <peterz@infradead.org>
To: luca abeni <luca.abeni@santannapisa.it>
Cc: Juri Lelli <juri.lelli@redhat.com>,
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: Fri, 19 Oct 2018 15:14:18 +0200 [thread overview]
Message-ID: <20181019131418.GI3121@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181018123332.6f33f715@luca64>
On Thu, Oct 18, 2018 at 12:33:32PM +0200, luca abeni wrote:
> Hi Peter,
>
> On Thu, 18 Oct 2018 11:48:50 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> [...]
> > > So, I tend to think that we might want to play safe and put some
> > > higher minimum value for dl_runtime (it's currently at 1ULL <<
> > > DL_SCALE). Guess the problem is to pick a reasonable value, though.
> > > Maybe link it someway to HZ? Then we might add a sysctl (or
> > > similar) thing with which knowledgeable users can do whatever they
> > > think their platform/config can support?
> >
> > 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.
>
> I agree with this.
>
>
> > And do we want to put the limit on runtime or on period ?
>
> I think we should have a minimum allowed runtime, a maximum allowed
> runtime, a minimum allowed period and a (per-user? per-control
> group?) maximum allowed utilization.
I was talking about a global !root max-u, but yes the cgroup max-u makes
definite sense as well.
> I suspect having a maximum period is useless, if we already enforce a
> maximum runtime.
Probably; yes. The asymmetry is unfortunate of course.
> > That is, something like:
> >
> > TICK_NSEC/2 < period < 10*TICK_NSEC
>
> As written above I would not enforce a maximum period.
I'm confused: 'period < 10*TICK_NSEC' reads like a max to me.
(irrespective of the argument on wether the max should be HZ related;
and I think you and Juri made good argument for it not to be)
> > and/or
> >
> > TICK_NSEC/2 < runtime < 10*TICK_NSEC
>
> I think (but I might be wrong) that "TICK_NSEC/2" is too large... I
> would divide the tick for a larger number (how many time do we want to
> allow the loop to run?)
It depends on how strict we want to enforce the no-interference rule.
The smaller we make this, the less accurate we enforce, the worse the
interference between tasks.
Note that we're only talking about a default; and HZ=100 is daft in any
case.
> And I think the maximum runtime should not be TICK-dependent... It is
> the maximum amount of time for which we allow the dealdine task to
> starve non-deadline tasks, so it should be an absolute time, not
> something HZ-dependent... No?
Agreed.
> > 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).
>
> Regarding capping u for users: some time ago, with Juri we discussed
> the idea of having per-cgroup limits on the deadline utilization... I
> think this is a good idea (and if the userspace creates a cgroup per
> user, this results in per-user capping - but it is more flexible in
> general)
Agreed, that makes sense.
next prev parent reply other threads:[~2018-10-19 13:14 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
2018-10-18 10:33 ` luca abeni
2018-10-19 13:14 ` Peter Zijlstra [this message]
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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