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xen-devel
Re: [Xen-devel] [PATCH] TSC scaling for live migration between platforms
On Thu, Jun 18, 2009 at 01:27:23PM -0700, Dan Magenheimer wrote:
> > Certainly Solaris relies on the TSC for time-keeping, and uses it very
> > heavily. To the extent that I doubt it's even feasible to migrate to a
> > machine where scaling needs to be done, and such a migration should be
> > refused, since it would essentially kill the guest.
>
> Hmmm... any numbers? Certainly Solaris isn't reading TSC much
# dtrace -n 'fbt::tsc_gethrtime:entry /cpu == 0/ { @ = sum(1); }' -c "sleep 10"
dtrace: description 'fbt::tsc_gethrtime:entry ' matched 1 probe
dtrace: pid 29708 has exited
27798
This is on a basically idle 8-way system. (The other CPUs are less busy.)
http://blogs.sun.com/eschrock/entry/microstate_accounting_in_solaris_10
> that data centers running Solaris guests must segregate sets of
> their machines by clock rate and disallow migrations
> between the sets?
Certainly for Solaris HVM that has to be the case until we make it use PV time
(presuming that is safe, which I'm not sure offhand).
> THAT expensive on x86? (If max(TSC/sec/processor)~=1000 and
> cycles/emulation~=5000, total degradation would be
> less than 1%. (Sounds high, but if the alternative is
At the end of the day, though, only testing will tell us for sure.
regards
john
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