On 2011-04-19 08:46, Roedel, Joerg wrote:
On Mon, Apr 18, 2011 at 08:02:35PM -0400, Zachary Amsden wrote:
On Sat, Apr 16, 2011 at 06:09:17PM +0200, Jan Kiszka wrote:
On 2011-03-25 09:44, Joerg Roedel wrote:
+ tsc_delta = !vcpu->arch.last_guest_tsc ? 0 :
+ tsc - vcpu->arch.last_guest_tsc;
This patch appears to cause troubles to Linux guests on TSC clocksource
and APIC highres timer. The first boot after qemu start is always fine,
but after a reboot the guest timer appears to fire incorrectly or even
not at all.
Was this patch tested with a guest reboot scenario as well? Does it
account for the TSC being reset to 0 on reboot?
Hmm, probably the last_guest_tsc is not updated correctly in this
scenario. I will have a look tomorrow.
Joerg
To avoid this problem, when the TSC is reset, the overshoot protection
where last_guest_tsc is used is specifically disabled:
/* Reset of TSC must disable overshoot protection below */
vcpu->arch.hv_clock.tsc_timestamp = 0;
vcpu->arch.last_tsc_write = data;
vcpu->arch.last_tsc_nsec = ns;
You can probably use the same test - last_guest_tsc is only valid if
tsc_timestamp above != 0.
Yes, this should also work. But the other way we get rid of
last_host_tsc which is also a good thing :)
That reminds me: I think we still have the bug that KVM overeagerly
declares the host's TSC unstable after resume from S3 because the TSC
appears to go backward when KVM checks. Or should this have been fixed now?
That should have been fixed... let me check if the patch has made it
upstream.
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