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Re: [Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen: drop anti-dependency on X86_VISWS
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Sat, 9 Apr 2011 11:34:52 +0100
Cc: "randy.dunlap@xxxxxxxxxx" <randy.dunlap@xxxxxxxxxx>, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, "eric.dumazet@xxxxxxxxx" <eric.dumazet@xxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, Miller <davem@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, "virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx" <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, "mingo@xxxxxxxxxx" <mingo@xxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx>, "tglx@xxxxxxxxxxxxx" <tglx@xxxxxxxxxxxxx>, "mirq-linux@xxxxxxxxxxxx" <mirq-linux@xxxxxxxxxxxx>, "pazke@xxxxxxxxx" <pazke@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, David
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On Fri, 2011-04-08 at 11:24 -0700, Jeremy Fitzhardinge wrote:
> On 04/08/2011 08:42 AM, Jan Beulich wrote:
> >>>> On 08.04.11 at 17:25, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> >> On 04/07/2011 11:38 PM, Ian Campbell wrote:
> >>> Is there any downside to this patch (is X86_CMPXCHG in the same sort of
> >>> boat?)
> >> Only if we don't use cmpxchg in shared memory with other domains or the
> >> hypervisor.  (I don't think it will dynamically switch between real and
> >> emulated cmpxchg depending on availability.)

We do use cmpxchg in the grant table code at least (actually,
sync_cmpxchng in that case).

> > Actually it does - see the "#ifndef CONFIG_X86_CMPXCHG" section
> > in asm/cmpxchg_32.h.
> Hm, OK.  Still, I'm happiest with that dependency in case someone
> knobbles the cpu to exclude cmpxchg and breaks things.

Dropping the TSC patch is sensible though?


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