On Wed, May 07, 2014 at 07:35:13PM -0300, Marcelo Tosatti wrote: > On Tue, May 06, 2014 at 03:27:20PM +0200, Ján Tomko wrote: > > Not yet merged in upstream QEMU: > > https://lists.gnu.org/archive/html/qemu-devel/2014-04/msg05024.html > > > > Add support for invariant TSC timer running at constant rate in > > all ACPI P-, C- and T-states. > > > > It can be enabled by specifying: > > <clock> > > <timer name='invtsc' present='yes'/> > > </clock> > > in the domain XML. > > > > Migration and saving the domain does not work with this timer. > > > > The support for this timer is indicated by bit 8 of EDX after calling > > CPUID with 0x80000007. It does not show up in /proc/cpuinfo [1] > > and since we're calling qemu without 'enforce', it doesn't error > > out if the host doesn't support this. > > It is not a timer, really, but a CPU flag. > > > Alternatively, we could expose it in libvirt as a cpu flag: > > <cpu mode='custom' match='exact'> > > <model fallback='forbid'>qemu64</model> > > <feature policy='require' name='invtsc'/> > > </cpu> > > Would prefer that option. Can't one modify QEMU's "-cpu" parameters, via > libvirt XML? > > > or maybe add +invtsc to qemu args when the 'nonstop_tsc' flag is > > requested? > > No, since it blocks migration better not condition "+invtsc" on > presence of 'nonstop_tsc' flag. Simply adding <feature name='invtsc'> <cpuid function='0x80000007' edx='0x00000100'/> </feature> To cpu_map.xml is sufficient to allow users to enable this feature on demand ? Haven't thought about all the corner cases, though. -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list