Re: [PATCH v3] softlockup: remove hung_task_check_count

From: Ingo Molnar
Date: Fri Jan 23 2009 - 04:23:29 EST

* Mandeep Baines <msb@xxxxxxxxxx> wrote:

> On Thu, Jan 22, 2009 at 11:55 AM, Mandeep Singh Baines <msb@xxxxxxxxxx> wrote:
> >
> > The unlock and lock could be removed and only compiled in if PREEMPT.
> > If the number of tasks isn't bound, the lock might be held too long.
> >
> This is incorrect. The adding the lock and unlock will not make the
> system more pre-emptive. To be more pre-emptive you'd want to check
> need_resched() as often as possible.
> > It would be kinda funny if hung_task caused a softlockup.
> >
> Again. This is incorrect. Rescheduling if need_resched() will prevent
> softlockup.
> Not sure what I was thinking this morning;)
> However, I am happy with the patch. To give writers a chance, the lock
> should held for bounded time. Holding the lock in khungtask (which is
> running at low scheduler priority) could potentially be delaying
> important work. The longer the lock is held, the bigger the priority
> inversion problem.

not sure i like the whole idea of removing the max iterations check. In
theory if there's a _ton_ of tasks, we could spend a lot of time looping
there. So it always looked prudent to limit it somewhat.

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