linux-kernel - Re: [PATCH v2 1/5] mutex: In mutex_can_spin_on_owner(), return false if task need

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Message-ID: <1390946460.2807.19.camel@j-VirtualBox>
Date:	Tue, 28 Jan 2014 14:01:00 -0800
From:	Jason Low <jason.low2@...com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	mingo@...hat.com, peterz@...radead.org, Waiman.Long@...com,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, riel@...hat.com,
	akpm@...ux-foundation.org, davidlohr@...com, hpa@...or.com,
	andi@...stfloor.org, aswin@...com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [PATCH v2 1/5] mutex: In mutex_can_spin_on_owner(), return
 false if task need_resched()

On Tue, 2014-01-28 at 12:20 -0800, Paul E. McKenney wrote:
> On Tue, Jan 28, 2014 at 11:13:12AM -0800, Jason Low wrote:
> > The mutex_can_spin_on_owner() function should also return false if the
> > task needs to be rescheduled to avoid entering the MCS queue when it
> > needs to reschedule.
> > 
> > Signed-off-by: Jason Low <jason.low2@...com>
> 
> Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> But I cannot help asking how this affects performance.  (My guess is
> "not much", but always good to know.)

Hi Paul,

In the past, when I tested this particular patch, I did not see any
noticeable performance gains. Patch 1 is really more of a "correctness"
change which was why I didn't retest this by itself. I can be sure to
include the benchmarks numbers on this particular patch though next
time.

Thanks.

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