On Wed, Dec 09, 2015 at 01:10:59PM -0800, Andy Lutomirski wrote: > I'm trying to clean up kvmclock and I can't get it to work at all. My > host is 4.4.0-rc3-ish on a Skylake laptop that has a working TSC. > > If I boot an SMP (2 vcpus) guest, tracing says: > > qemu-system-x86-2517 [001] 102242.610654: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 0 > qemu-system-x86-2521 [000] 102242.613742: kvm_track_tsc: > vcpu_id 0 masterclock 0 offsetmatched 0 nr_online 1 hostclock tsc > qemu-system-x86-2522 [000] 102242.622959: kvm_track_tsc: > vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc > qemu-system-x86-2521 [000] 102242.645123: kvm_track_tsc: > vcpu_id 0 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc > qemu-system-x86-2522 [000] 102242.647291: kvm_track_tsc: > vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc > qemu-system-x86-2521 [000] 102242.653369: kvm_track_tsc: > vcpu_id 0 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc > qemu-system-x86-2522 [000] 102242.653429: kvm_track_tsc: > vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc > qemu-system-x86-2517 [001] 102242.653447: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 1 > qemu-system-x86-2521 [000] 102242.653657: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 1 > qemu-system-x86-2522 [002] 102242.664448: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 1 > > > If I boot a UP guest, tracing says: > > qemu-system-x86-2567 [001] 102370.447484: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 1 > qemu-system-x86-2571 [002] 102370.447688: kvm_update_master_clock: > masterclock 0 hostclock tsc offsetmatched 1 > > I suspect, but I haven't verified, that this is fallout from: > > commit 16a9602158861687c78b6de6dc6a79e6e8a9136f > Author: Marcelo Tosatti <mtosatti@xxxxxxxxxx> > Date: Wed May 14 12:43:24 2014 -0300 > > KVM: x86: disable master clock if TSC is reset during suspend > > Updating system_time from the kernel clock once master clock > has been enabled can result in time backwards event, in case > kernel clock frequency is lower than TSC frequency. > > Disable master clock in case it is necessary to update it > from the resume path. > > Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > > Can we please stop making kvmclock more complex? It's a beast right > now, and not in a good way. It's far too tangled with the vclock > machinery on both the host and guest sides, the pvclock stuff is not > well thought out (even in principle in an ABI sense), and it's never > been clear to my what problem exactly the kvmclock stuff is supposed > to solve. > > > I'm somewhat tempted to suggest that we delete kvmclock entirely and > start over. A correctly functioning KVM guest using TSC (i.e. > ignoring kvmclock entirely) seems to work rather more reliably and > considerably faster than a kvmclock guest. > > --Andy Users can do that, if they want. "clocksource=tsc" kernel option. -- 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
