linux-kernel - Re: [RFC][PATCH 2/2] add a counter for writers spinning on a rwlock

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Message-Id: <1232991701.4863.222.camel@laptop>
Date:	Mon, 26 Jan 2009 18:41:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mandeep Baines <msb@...gle.com>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 2/2] add a counter for writers spinning on a rwlock

On Mon, 2009-01-26 at 09:36 -0800, Mandeep Baines wrote:

> Unfortunately, this can't be done for hung_task. It writes to the
> task_struct here:

Don't top post!

> static void check_hung_task(struct task_struct *t, unsigned long now,
>                             unsigned long timeout)
> {
>         unsigned long switch_count = t->nvcsw + t->nivcsw;
> 
>         if (t->flags & PF_FROZEN)
>                 return;
> 
>         if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
>                 t->last_switch_count = switch_count;
>                 t->last_switch_timestamp = now;
>                 return;
>         }
> 
> It is able to get away with using only a read_lock because no one else
> reads or writes to these fields.

How would RCU be different here?

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