On Tue, Jun 21, 2011 at 11:56:26AM +0300, Avi Kivity wrote: > On 06/21/2011 11:41 AM, Gleb Natapov wrote: > >On Tue, Jun 21, 2011 at 11:09:21AM +0300, Avi Kivity wrote: > >> On 06/21/2011 09:02 AM, Gleb Natapov wrote: > >> >On Mon, Jun 20, 2011 at 07:34:57PM +0300, Avi Kivity wrote: > >> >> >The only two things which came to my mind are: > >> >> > > >> >> > * NMI (aka. ipmitool diag) - already available in qemu/kvm - but requires > >> >> > in-guest kexec/kdump > >> >> > * Hardware-Watchdog (also available in qemu/libvirt) > >> >> > >> >> A watchdog has the advantage that is also detects lockups. > >> >> > >> >And has disadvantage that all time base heuristics are bite us in the > >> >end. > >> > >> The perf-based watchdog counts clocks-not-halted, not time, so it is > >> safe from time issues. > >So it counts only instruction that guest actually executed? That's > >perfect then. How much overhead it has in a guest though? > > Should be pretty low, especially if the guest is idle. There were > some negative reports about the pmu From David Ahern, so it needs to > be verified. But it will be running not only when the guest is idle. > > > >> We could make the hardware watchdog cheat in > >> the same way. > >> > >Something like steal time, but for watchdog. But this become complicated fast. > >Watchdog emulation will have to move into kernel for starter. > > Why? You can use a performance counter from userspace. > Heh, haven't thought about such way of implementing watchdog device. But the same question again: what impact on performance constantly running guest under perf is? Doesn't running guest under perf involve a lot of NMIs (and hence vmexists)? -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
