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[Xen-devel] pvclock (PV and HVM) and vsyscall

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Subject: [Xen-devel] pvclock (PV and HVM) and vsyscall
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Fri, 15 Oct 2010 08:48:14 -0700 (PDT)
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The other discussion of RADclock reminded me:

IIRC the pvclock algorithm is still incompatible with
vsyscall/vdso (fast system calls) and there was no obvious
and upstreamable solution to resolve this.

This means that any userland call to the various gettimeofday
routines will always do a true system call on both (a) a PV
domain or (b) any PV on HVM domain with Stefanos' pvclock patch.

Since true syscalls are very expensive on a 64-bit
PV domain, I'm wondering if pvclock is still the right
default choice for upstream (at least for 64-bit).

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