Date: Sun, 15 Jun 2014 15:16:54 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-arch@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
        Paolo Bonzini <paolo.bonzini@gmail.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Oleg Nesterov <oleg@redhat.com>, Gleb Natapov <gleb@redhat.com>,
        Scott J Norton <scott.norton@hp.com>, Chegu Vinod <chegu_vinod@hp.com>
Subject: Re: [PATCH v11 14/16] pvqspinlock: Add qspinlock para-virtualization
 support
Message-ID: <20140615131654.GJ11371@laptop.programming.kicks-ass.net>
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On Thu, Jun 12, 2014 at 04:48:41PM -0400, Waiman Long wrote:
> I don't have a good understanding of the kernel alternatives mechanism.

I didn't either; I do now, cost me a whole day reading up on
alternative/paravirt code patching.

See the patches I just send out; I got the 'native' case with paravirt
enabled to be one NOP worse than the native case without paravirt -- for
queue_spin_unlock.

The lock slowpath is several nops and some pointless movs more expensive.
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