linux-kernel - Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits with HZ/20

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Message-ID: <20f4de24-d7f1-4a10-bb32-b9d39773c9a6@paulmck-laptop>
Date:   Fri, 25 Aug 2023 18:31:56 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>, rcu@...r.kernel.org
Subject: Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits
 with HZ/20

On Fri, Aug 25, 2023 at 02:55:38AM +0000, Joel Fernandes wrote:
> On Wed, Aug 23, 2023 at 02:07:55PM -0700, Paul E. McKenney wrote:
> > On Wed, Aug 16, 2023 at 08:49:12PM +0000, Joel Fernandes (Google) wrote:
> > > In the past, we see that spinning on schedule_timeout* with a wait of 1
> > > jiffie can hang the kernel. See d52d3a2bf408 ("torture: Fix hang during
> > > kthread shutdown phase").
> > > 
> > > Recently again it showed up in torture's stutter code as well. The behavior is
> > > the the function may instantly return and never go to sleep preempting whatever
> > > was running under it.
> > > 
> > > To prevent future issues, apply the same fix mentioned in the above
> > > commit d52d3a2bf408 to more places.
> > > 
> > > I took care to only apply it to places where I thought it made sense.
> > > 
> > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > 
> > Hearing no objections, I applied this for further review and testing.
> > 
> > In the future, should some of these become hrtimers?
> 
> Yes they certainly could be but we don't need these ones to be high
> resolution AFAICS and the jiffie granularity should be good.

True, but wouldn't avoiding the repeated wakeups, even at the lower
frequency, be of some value?

							Thanx, Paul