linux-kernel - Re: [PATCH v4] softlockup: remove hung_task_check

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Message-ID: <20090127132626.GH23121@elte.hu>
Date:	Tue, 27 Jan 2009 14:26:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mandeep Singh Baines <msb@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	rientjes@...gle.com, mbligh@...gle.com, thockin@...gle.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4] softlockup: remove hung_task_check_count


* Mandeep Singh Baines <msb@...gle.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.

	Ingo
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