linux-kernel - Re: [PATCH 2/2] locking/mutex,rwsem: Reduce vcpu_is

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Date:   Wed, 8 Feb 2017 14:09:26 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jeremy Fitzhardinge <jeremy@...p.org>,
        Chris Wright <chrisw@...s-sol.org>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH 2/2] locking/mutex,rwsem: Reduce vcpu_is_preempted()
 calling frequency

On 02/08/2017 02:05 PM, Peter Zijlstra wrote:
> On Wed, Feb 08, 2017 at 01:00:25PM -0500, Waiman Long wrote:
>> As the vcpu_is_preempted() call is pretty costly compared with other
>> checks within mutex_spin_on_owner() and rwsem_spin_on_owner(), they
>> are done at a reduce frequency of once every 256 iterations.
> That's just disgusting.

I do have some doubt myself on the effectiveness of this patch. Anyway,
it is the first patch that I think is more beneficial.

Cheers,
Longman