I was fretting about the overhead of emulating TSC in guest kernels. Is it possible (and relatively inexpensive) to change CR4.TSD on every transition between guest kernel and userland? I suspect not, but thought I''d check. If so, what about HVM vs PV and 32-bit vs 64-bit guest. Thanks, Dan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
It''s only likely to be reasonable for PV 64-bit guests, which transition via the hypervisor already for guest-kernel <-> guest-app transitions (i.e., those transition times suck already). -- Keir On 21/09/2009 23:49, "Dan Magenheimer" <dan.magenheimer@oracle.com> wrote:> I was fretting about the overhead of emulating TSC in > guest kernels. Is it possible (and relatively inexpensive) > to change CR4.TSD on every transition between guest > kernel and userland? I suspect not, but thought > I''d check. If so, what about HVM vs PV and 32-bit > vs 64-bit guest. > > Thanks, > Dan > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
>>> Keir Fraser <keir.fraser@eu.citrix.com> 22.09.09 08:34 >>> >It''s only likely to be reasonable for PV 64-bit guests, which transition via >the hypervisor already for guest-kernel <-> guest-app transitions (i.e., >those transition times suck already).But still, I don''t think adding a serializing instruction that likely (I don''t know of officially available numbers) takes hundreds of clocks is a good thing to do. Jan>On 21/09/2009 23:49, "Dan Magenheimer" <dan.magenheimer@oracle.com> wrote: >> I was fretting about the overhead of emulating TSC in >> guest kernels. Is it possible (and relatively inexpensive) >> to change CR4.TSD on every transition between guest >> kernel and userland? I suspect not, but thought >> I''d check. If so, what about HVM vs PV and 32-bit >> vs 64-bit guest._______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel