linux-kernel - Re: [RFC PATCH 1/3] locking/mutex: Try to acquire mutex only if it is unlocked

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Message-ID: <1401996117.6680.33.camel@j-VirtualBox>
Date:	Thu, 05 Jun 2014 12:21:57 -0700
From:	Jason Low <jason.low2@...com>
To:	Waiman Long <waiman.long@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	tim.c.chen@...ux.intel.com, peter@...leysoftware.com,
	riel@...hat.com, hpa@...or.com, walken@...gle.com,
	davidlohr@...com, aswin@...com, scott.norton@...com,
	chegu_vinod@...com
Subject: Re: [RFC PATCH 1/3] locking/mutex: Try to acquire mutex only if it
 is unlocked

On Wed, 2014-06-04 at 23:24 -0400, Waiman Long wrote:
> On 06/04/2014 05:26 PM, Jason Low wrote:
> > On Wed, 2014-06-04 at 21:43 +0200, Peter Zijlstra wrote:
> >> Please make them inline functions, also can we rename the SHOW_NO_WAITER
> >> thing, because its not at all clear to me wtf it does; should it be
> >> called: mutex_no_waiters() or somesuch?
> > Okay, I can make them inline functions. I mainly added the macro to keep
> > it consistent with the MUTEX_SHOW_NO_WAITER() check, but we can surely
> > make this more clear. mutex_no_waiters() sounds fine, or perhaps
> > something like mutex_has_no_waiters()?
> >
> 
> You can remove the MUTEX_SHOW_NO_WAITER macro as all the call sites are 
> to be replaced.

Sure.

> I didn't check directly for unlocked count because of 
> fairness concern in my original patch, but I think checking directly for 
> unlocked count should be fine too.

Can you elaborate on the "fairness concern"? In the current code, we're
already directly checking for unlocked count in
atomic_read(&lock->count) == 1 if that's what you're referring to.

Thanks,
Jason

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