linux-kernel - Re: [PATCH 3/4] paravirt: add virt_spin

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Message-ID: <20170906070816.s6rtgtqpljnbudux@hirez.programming.kicks-ass.net>
Date:   Wed, 6 Sep 2017 09:08:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org, jeremy@...p.org,
        chrisw@...s-sol.org, akataria@...are.com, rusty@...tcorp.com.au,
        boris.ostrovsky@...cle.com, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com
Subject: Re: [PATCH 3/4] paravirt: add virt_spin_lock pvops function


Guys, please trim email.

On Tue, Sep 05, 2017 at 10:31:46AM -0400, Waiman Long wrote:
> For clarification, I was actually asking if you consider just adding one
> more jump label to skip it for Xen/KVM instead of making
> virt_spin_lock() a pv-op.

I don't understand. What performance are you worried about. Native will
now do: "xor rax,rax; jnz some_cold_label" that's fairly trival code.