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xen-devel
Re: [Xen-devel] [PATCH RFC 03/12] x86/ticketlock: Use C for __ticket_spi
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
Re: [Xen-devel] [PATCH RFC 03/12] x86/ticketlock: Use C for __ticket_spin_unlock |
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From: |
"H. Peter Anvin" <hpa@xxxxxxxxx> |
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Date: |
Fri, 06 Aug 2010 10:47:23 -0700 |
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Cc: |
Nick Piggin <npiggin@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx> |
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On 07/20/2010 09:17 AM, Jeremy Fitzhardinge wrote:
>
> "volatile" would be a compiler barrier, but it has no direct effect on,
> or relevence to, the CPU. It just cares about the LOCK_PREFIX. The
> "memory" clobber is probably unnecessary as well, since the constraints
> already tell the compiler the most important information. We can add
> barriers separately as needed.
>
You absolutely need volatile, since otherwise you're permitting the
compiler to split, re-execute or even drop the code. Anything else
might work, by accident, but it's not clean.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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