linux-kernel - Re: [PATCH] sched: remove unreliable pointer in mutex_spin_on

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Date:	Mon, 13 Jun 2011 09:14:57 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] sched: remove unreliable pointer in
 mutex_spin_on_owner()

On Sat, 2011-06-11 at 22:37 +0800, Hillf Danton wrote:

> Unlike spinner and owner that are well considered, there are waiters, please
> see the following homework.
> 
> Another question about CONFIG_MUTEX_SPIN_ON_OWNER, from the view angle of
> spinners, as you mentioned above, looks like that they are crowding on a bus
> as violently as they could, in contrast to the Japanese people in earthquake.
> 
> Then the result could be, out of our image, not as optimistic as it is, since
> a thread of lower priority could out-compete another of higher priority,
> when a bunch of spinners are simultaneously trying hard to acquire the mutex,
> though only one is allowed to get award.

Note, we don't care about priorities here. If you care about that, then
use the -rt patched kernel and enable "PREEMPT_RT". Because that changes
the mutex code to be priority driven (uses rt_mutex instead of mutex).
In a year or two (or three ;) the -rt patch will be part of the kernel
and you will be able to get these things for free.

-- Steve


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