On Wed, Jan 21, 2015 at 3:15 PM, Peter Jeremy <peter_at_rulingia.com> wrote: > On 2015-Jan-04 11:56:14 -0600, Bryan Venteicher < > bryanv_at_daemoninthecloset.org> wrote: > >For the last few weeks, I've been working on adding support for KVM clock > >in the projects/paravirt branch. Currently, a KVM VM guest will end up > >selecting either the HPET or ACPI as the timecounter source. > Unfortunately, > >this is very costly since every timecounter fetch causes a VM exit. KVM > >clock allows the guest to use the TSC instead; it is very similar to the > >existing Xen timer. > > A somewhat late response but have you looked at > > https://github.com/blitz/freebsd/commit/cdc5f872b3e48cc0dda031fc7d6bdedc65c3148f > I've been running this[*] on a Google Compute Engine instance for about 6 > months without problems. > > A goal of my work was to put a bit of infrastructure in place so FreeBSD can support pvops across a variety of hypervisors. KVMCLOCK happens to be about the easiest to implement, and has a decent performance win for many situations. I think that commit is broken on SMP guests: CPU_FOREACH() does not switch the current CPU, so it just keeps writing to the MSR on the BSP. [*] I had to patch out the test for KVM_FEATURE_CLOCKSOURCE_STABLE_BIT but > I think that's a GCE issue. > > -- > Peter Jeremy >Received on Thu Jan 22 2015 - 00:06:47 UTC
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