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xen-devel
[Xen-devel] Re: [PATCH 00/20] x86: ticket lock rewrite and paravirtualiz
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 00/20] x86: ticket lock rewrite and paravirtualization |
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From: |
"H. Peter Anvin" <hpa@xxxxxxxxx> |
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Date: |
Fri, 12 Nov 2010 14:12:35 -0800 |
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Cc: |
Nick Piggin <npiggin@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx> |
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Fri, 12 Nov 2010 14:15:48 -0800 |
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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
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