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Re: [Xen-devel] write_tsc in a PV domain?

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] write_tsc in a PV domain?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 31 Aug 2009 12:18:39 -0700
Cc: "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
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On 08/31/09 11:11, Dan Magenheimer wrote:
> I'm experimenting with clock_gettime(), gettimeofday(),
> and rdtsc with a 2.6.30 64-bit pvguest.  I have tried both
> with kernel.vsyscall64 equal to 0 and 1 (but haven't seen
> any significant difference between the two).  I have
> confirmed from sysfs that clocksource=xen

Yeah, as I said, I wouldn't expect vsyscall to work under Xen at the
moment; the Xen clocksource will disable it.  Clocksources can implement
a "vread" method for use from a vsyscall, but from a quick look it
didn't appear we could use it as-is (because the pvclock info isn't
mapped into userspace, and the current vsyscall code assumes a single
set of parameters rather than percpu).


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