linux-kernel - Re: [RFC][PATCH 3/3] locking/mutex: Add lock handoff to avoid starvation

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Message-ID: <20160823203204.GU10153@twins.programming.kicks-ass.net>
Date:   Tue, 23 Aug 2016 22:32:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <waiman.long@....com>
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>
Subject: Re: [RFC][PATCH 3/3] locking/mutex: Add lock handoff to avoid
 starvation

On Tue, Aug 23, 2016 at 03:47:53PM -0400, Waiman Long wrote:
> On 08/23/2016 08:46 AM, Peter Zijlstra wrote:
> >N
> >@@ -573,8 +600,14 @@ __mutex_lock_common(struct mutex *lock,
> >  		schedule_preempt_disabled();
> >  		spin_lock_mutex(&lock->wait_lock, flags);
> >
> >+		if (__mutex_owner(lock) == current)
> >+			break;
> >+
> >  		if (__mutex_trylock(lock))
> >  			break;
> >+
> >+		if (__mutex_waiter_is_first(lock,&waiter))
> >+			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
> >  	}
> >  	__set_task_state(task, TASK_RUNNING);
> >
> >
> 
> You may want to think about doing some spinning while the owner is active
> instead of going back to sleep again here.

For sure; I just didn't bother pulling in your patches. I didn't want to
sink in more time in case people really hated on 1/3 ;-)