Re: [Qemu-devel] [PATCH] kvmclock: Ensure time in migration never goes backward

[Marcelo Tosatti]

On Tue, May 06, 2014 at 09:54:35PM +0200, Marcin Gibuła wrote:
> >Yes, and it isn't. Any ideas why it's not? This patch really just uses
> >the guest visible kvmclock time rather than the host view of it on
> >migration.
> >
> >There is definitely something very broken on the host's side since it
> >does return a smaller time than the guest exposed interface indicates.
> 
> Don't know if helps but here are example values from
> time_at_migration and s->clock from your patch.
> 
> Tested on 5 restores of saved VM that (used to) hang:
> 
>    s->clock      time_at_migration
> 157082235125698  157113284546655
> 157082235125698  157113298196976
> 157082235125698  157113284615117
> 157082235125698  157113284486601
> 157082235125698  157113284479740
> 
> Now, when I compare system time on guest with and without patch:
> 
> On unpatched qemu vm restores with date: Apr 18 06:56:36
> On patched qemu it says: Apr 18 06:57:06
> 
> -- 
> mg

Marcin,

Can you turn off the TSC clock on the host and attempt to reproduce the 
issue, without Alexander's patch? 

Just 

echo hpet > /sys/devices/system/clocksource/clocksource0/current_clocksource

(or any other clock except tsc if you don't have hpet).
TIA.