linux-kernel - Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly

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Message-ID: <m2r4p7u5pk.fsf@firstfloor.org>
Date:	Tue, 09 Oct 2012 06:37:27 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Ivo Sieben <meltedpianoman@...il.com>
Cc:	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	<linux-serial@...r.kernel.org>, Alan Cox <alan@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly

Ivo Sieben <meltedpianoman@...il.com> writes:

> Check the waitqueue task list to be non empty before entering the critical
> section. This prevents locking the spin lock needlessly in case the queue
> was empty, and therefor also prevent scheduling overhead on a PREEMPT_RT
> system.
>
> Signed-off-by: Ivo Sieben <meltedpianoman@...il.com>
> ---
>
>  REPOST:
>  Request for comments:
>  - Does this make any sense?

Looks good to me. Avoiding any spinlock is good.  I don't even think you
need "careful", if you miss an update it was just as it happened a
little later.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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