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Date: Fri, 12 Nov 2010 14:12:35 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nick Piggin <npiggin@suse.de>, Jan Beulich <JBeulich@novell.com>,
        Avi Kivity <avi@redhat.com>, Xen-devel <xen-devel@lists.xensource.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Subject: Re: [PATCH 00/20] x86: ticket lock rewrite and paravirtualization
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On 11/03/2010 07:59 AM, Jeremy Fitzhardinge wrote:
> 
>       - with an unmodified struct spinlock, it can check to see if
>         head == tail after unlock; if not, then there's someone else
>         trying to lock, and we can do a kick.  Unfortunately this
>         generates very high level of redundant kicks, because the
>         waiting CPU might not have blocked yet (which is the common
>         case)
> 

How high is "very high" here -- most of the time (so that any mitigation
on the slow patch is useless)?

	-hpa