From: Peter Zijlstra <peterz@infradead.org>
To: Mandeep Singh Baines <msb@google.com>
Cc: "Ingo Molnar" <mingo@elte.hu>,
linux-kernel@vger.kernel.org,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
rientjes@google.com, mbligh@google.com, thockin@google.com,
"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH v4] softlockup: remove hung_task_check_count
Date: Wed, 28 Jan 2009 09:25:00 +0100 [thread overview]
Message-ID: <1233131100.10992.43.camel@laptop> (raw)
In-Reply-To: <20090127184851.GD22298@google.com>
On Tue, 2009-01-27 at 10:48 -0800, Mandeep Singh Baines wrote:
> Ingo Molnar (mingo@elte.hu) wrote:
> >
> > * Mandeep Singh Baines <msb@google.com> wrote:
> >
> > > The design was proposed by Frédéric Weisbecker. Peter Zijlstra suggested
> > > the use of RCU.
> >
> > ok, this looks _much_ cleaner.
> >
> > One question:
> >
> > > - read_lock(&tasklist_lock);
> > > + rcu_read_lock();
> > > do_each_thread(g, t) {
> > > - if (!--max_count)
> > > + if (need_resched())
> > > goto unlock;
> >
> > Isnt it dangerous to skip a check just because we got marked for
> > reschedule? Since it runs so rarely it could by accident be preempted and
> > we'd not get any checking done for a long time.
> >
>
> Yeah, the checking could be deferred indefinitely. So you could have a system
> where tasks are hung but it takes a really long time to detect this and
> finally panic the system. Not so good for high-availability.
Why break out at all? Are you that worried about khungtaskd introducing
latencies? Is using preemptible RCU an option for you?
next prev parent reply other threads:[~2009-01-28 8:25 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-25 20:50 [RFC][PATCH 2/2] add a counter for writers spinning on a rwlock Frederic Weisbecker
2009-01-26 13:32 ` Ingo Molnar
2009-01-26 13:48 ` Peter Zijlstra
2009-01-26 15:25 ` Frédéric Weisbecker
2009-01-26 15:37 ` Peter Zijlstra
2009-01-26 16:04 ` Frédéric Weisbecker
2009-01-26 17:36 ` Mandeep Baines
2009-01-26 17:41 ` Peter Zijlstra
2009-01-27 0:30 ` [PATCH v4] softlockup: remove hung_task_check_count Mandeep Singh Baines
2009-01-27 9:27 ` Frederic Weisbecker
2009-01-27 13:26 ` Ingo Molnar
2009-01-27 18:48 ` Mandeep Singh Baines
2009-01-28 8:25 ` Peter Zijlstra [this message]
2009-01-29 1:42 ` Mandeep Singh Baines
2009-01-30 20:41 ` Mandeep Singh Baines
2009-01-30 20:46 ` [PATCH 1/2] softlockup: convert read_lock in hung_task to rcu_read_lock Mandeep Singh Baines
2009-01-30 20:49 ` [PATCH 2/2] softlockup: check all tasks in hung_task Mandeep Singh Baines
2009-01-31 19:22 ` Peter Zijlstra
2009-02-03 0:05 ` [PATCH 2/2 v2] " Mandeep Singh Baines
2009-02-03 12:23 ` Ingo Molnar
2009-02-03 20:56 ` [PATCH 2/2 v3] " Mandeep Singh Baines
2009-02-04 19:43 ` Ingo Molnar
2009-02-05 4:35 ` [PATCH 2/2 v4] " Mandeep Singh Baines
2009-02-05 14:34 ` Ingo Molnar
2009-02-05 17:48 ` Andrew Morton
2009-02-05 18:07 ` Ingo Molnar
2009-02-05 18:30 ` Andrew Morton
2009-02-05 18:58 ` Ingo Molnar
2009-02-05 18:40 ` Mandeep Singh Baines
2009-02-05 17:56 ` [PATCH] softlockup: convert read_lock in hung_task to rcu_read_lock Mandeep Singh Baines
2009-02-05 18:13 ` Ingo Molnar
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