Date: Fri, 23 Jan 2009 10:23:06 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Mandeep Baines <msb@google.com>
Cc: fweisbec@gmail.com, linux-kernel@vger.kernel.org, rientjes@google.com,
       mbligh@google.com, thockin@google.com
Subject: Re: [PATCH v3] softlockup: remove hung_task_check_count
Message-ID: <20090123092306.GB29820@elte.hu>
References: <20090122083457.GC7438@elte.hu> <20090122195513.GA22146@google.com> <1fe6c7900901221921m586b129dwf8c3446f897b57f0@mail.gmail.com>
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* Mandeep Baines <msb@google.com> wrote:

> On Thu, Jan 22, 2009 at 11:55 AM, Mandeep Singh Baines <msb@google.com> 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.

	Ingo
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