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.
Zach
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