linux-kernel - Re: [PATCH -v4 8/8] locking/mutex: Enable optimistic spinning of woken waiter

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Message-ID: <58055CF8.2060806@hpe.com>
Date:   Mon, 17 Oct 2016 19:21:28 -0400
From:   Waiman Long <waiman.long@....com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason Low <jason.low2@....com>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <Will.Deacon@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Imre Deak <imre.deak@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Terry Rudd <terry.rudd@....com>,
        "Paul E. McKenney" <paulmck@...ibm.com>,
        Jason Low <jason.low2@...com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH -v4 8/8] locking/mutex: Enable optimistic spinning of
 woken waiter

On 10/07/2016 10:52 AM, Peter Zijlstra wrote:
> @@ -600,7 +630,7 @@ __mutex_lock_common(struct mutex *lock,
>   	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
>
>   	if (__mutex_trylock(lock, false) ||
> -	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
> +	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
>   		/* got the lock, yay! */
>   		lock_acquired(&lock->dep_map, ip);
>   		if (use_ww_ctx)
> @@ -669,7 +699,8 @@ __mutex_lock_common(struct mutex *lock,
>   		 * state back to RUNNING and fall through the next schedule(),
>   		 * or we must see its unlock and acquire.
>   		 */
> -		if (__mutex_trylock(lock, first))
> +		if ((first&&  mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, true)) ||
> +		     __mutex_trylock(lock, first))

Do we need a __mutex_trylock() here? mutex_optimistic_spin() will do the 
trylock and we have one at the top of the loop.

Cheers,
Longman