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Date:   Wed, 8 Nov 2017 00:40:05 -0800
From:   Eduardo Valentin <eduval@amazon.com>
To:     Waiman Long <longman@redhat.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Juergen Gross" <jgross@suse.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Eduardo Valentin <eduval@amazon.com>
Subject: Re: [PATCH v2] locking/pvqspinlock: Hybrid PV queued/unfair locks
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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@redhat.com>

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

-- 
All the best,
Eduardo Valentin

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