linux-kernel - Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic

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Date:	Sat, 13 Feb 2016 10:14:18 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Waiman Long <Waiman.Long@....com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ding Tianhong <dingtianhong@...wei.com>,
	Jason Low <jason.low2@....com>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <Will.Deacon@....com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to
 mutex_optimistic_spin()

On Sat, 13 Feb 2016, Peter Zijlstra wrote:

>Can't see it do that, also, if it were to do that, we'd not be here
>since having a waiter would then mean no spinners and no starvation
>etc..

I was having a hard time understanding why on earth you didn't see that. And yes
I was also wondering why it was even there... but I was looking at -next, where we
have Ding's original patch b9ce3647b4901071b0dd35d62954a4bb0e5ba1d1.... Paul, could
you drop this patch?

But yeah, I do agree that waiters should also do the mutex_can_spin_on_owner()
check unless I'm missing something subtle from Waiman.

Thanks,
Davidlohr