linux-kernel - Re: [PATCH v2] locking/pvqspinlock: Hybrid PV queued/unfair locks

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Date:   Wed, 8 Nov 2017 00:40:05 -0800
From:   Eduardo Valentin <eduval@...zon.com>
To:     Waiman Long <longman@...hat.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Juergen Gross" <jgross@...e.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Eduardo Valentin <eduval@...zon.com>
Subject: Re: [PATCH v2] locking/pvqspinlock: Hybrid PV queued/unfair locks

On Tue, Nov 07, 2017 at 04:18:06PM -0500, Waiman Long wrote:
> Currently, all the lock waiters entering the slowpath will do one
> lock stealing attempt to acquire the lock. That helps performance,
> especially in VMs with over-committed vCPUs. However, the current
> pvqspinlocks still don't perform as good as unfair locks in many cases.
> On the other hands, unfair locks do have the problem of lock starvation
> that pvqspinlocks don't have.
> 
> This patch combines the best attributes of an unfair lock and a
> pvqspinlock into a hybrid lock with 2 modes - queued mode & unfair
> mode. A lock waiter goes into the unfair mode when there are waiters
> in the wait queue but the pending bit isn't set. Otherwise, it will
> go into the queued mode waiting in the queue for its turn.
> 

> 
> Signed-off-by: Waiman Long <longman@...hat.com>

Reviewed-by: Eduardo Valentin <eduval@...zon.com>

-- 
All the best,
Eduardo Valentin