From: Peng Liu <iwtbavbm@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, valentin.schneider@arm.com,
raistlin@linux.it, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/2] sched/deadline: optimize sched_dl_global_validate()
Date: Thu, 8 Oct 2020 21:58:07 +0800 [thread overview]
Message-ID: <20201008135807.GA29010@iZj6chx1xj0e0buvshuecpZ> (raw)
In-Reply-To: <20201007165533.GL2628@hirez.programming.kicks-ass.net>
On Wed, Oct 07, 2020 at 06:55:33PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 07, 2020 at 11:12:29PM +0800, Peng Liu wrote:
> > +/* Used for dl_bw check and update. */
> > +static u32 dl_generation;
>
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 28709f6b0975..53477e8b26b0 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -798,6 +798,13 @@ struct root_domain {
> > */
> > cpumask_var_t dlo_mask;
> > atomic_t dlo_count;
> > +
> > + /*
> > + * Indicate whether a root_domain's dl_bw has been checked or
> > + * updated. It's monotonously increasing, then wrap around.
> > + */
> > + u32 visit_gen;
> > +
> > struct dl_bw dl_bw;
> > struct cpudl cpudl;
> >
> > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> > index dd7770226086..90f3e5558fa2 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -516,6 +516,7 @@ static int init_rootdomain(struct root_domain *rd)
> > init_irq_work(&rd->rto_push_work, rto_push_irq_work_func);
> > #endif
> >
> > + rd->visit_gen = 0;
> > init_dl_bw(&rd->dl_bw);
> > if (cpudl_init(&rd->cpudl) != 0)
> > goto free_rto_mask;
>
> I'm fairly sure I made the generation a u64, the above is susceptible to
> a false positive due to wrap-around.
>
> Increase the generation to -1, create a new root domain, then the next
> generation is 0 and we'll skip the new domain, even though it should be
> updated.
Ah... at first, I also thought that u32 is "big enough" given that
no one would frequently change the settings, 'wrap-around' shouldn't
be a concern.
So...OK, I will revert it back to u64. What a big circle! :)
Thanks for your time!
next prev parent reply other threads:[~2020-10-08 13:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 15:11 [PATCH v5 0/2] sched/deadline: Fix and optimize sched_dl_global_validate() Peng Liu
2020-10-07 15:12 ` [PATCH v5 1/2] sched/deadline: " Peng Liu
2020-10-07 16:55 ` Peter Zijlstra
2020-10-08 13:58 ` Peng Liu [this message]
2020-10-07 15:13 ` [PATCH v5 2/2] sched/deadline: Fix sched_dl_global_validate() Peng Liu
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