* Re: [Qemu-devel] [patch 0/2] add QMP command to reset rtc interrupt backlog
[not found] <20140530140523.653892288@amt.cnet>
@ 2014-06-02 9:13 ` Michal Privoznik
2014-06-02 16:31 ` Marcelo Tosatti
0 siblings, 1 reply; 2+ messages in thread
From: Michal Privoznik @ 2014-06-02 9:13 UTC (permalink / raw)
To: Marcelo Tosatti, qemu-devel; +Cc: gleb, pbonzini, armbru
On 30.05.2014 16:05, Marcelo Tosatti wrote:
> It is necessary to reset RTC interrupt backlog if guest time is
> synchronized via a different mechanism, such as QGA's guest-set-time
> command.
>
> Failing to do so causes both corrections to be applied (summed),
> resulting in an incorrect guest time.
>
>
Marcelo,
what happens if quest is synchronized via NTP? Does this command still
need to be executed after 'cont'?
Michal
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Qemu-devel] [patch 0/2] add QMP command to reset rtc interrupt backlog
2014-06-02 9:13 ` [Qemu-devel] [patch 0/2] add QMP command to reset rtc interrupt backlog Michal Privoznik
@ 2014-06-02 16:31 ` Marcelo Tosatti
0 siblings, 0 replies; 2+ messages in thread
From: Marcelo Tosatti @ 2014-06-02 16:31 UTC (permalink / raw)
To: Michal Privoznik; +Cc: gleb, pbonzini, qemu-devel, armbru
On Mon, Jun 02, 2014 at 11:13:15AM +0200, Michal Privoznik wrote:
> On 30.05.2014 16:05, Marcelo Tosatti wrote:
> >It is necessary to reset RTC interrupt backlog if guest time is
> >synchronized via a different mechanism, such as QGA's guest-set-time
> >command.
> >
> >Failing to do so causes both corrections to be applied (summed),
> >resulting in an incorrect guest time.
> >
> >
>
> Marcelo,
>
> what happens if quest is synchronized via NTP? Does this command
> still need to be executed after 'cont'?
>
> Michal
Yes because NTP will either take time to adjust by slewing or step the
clock (which renders guest-set-time() unuseable). During that time,
guest clock will be ahead of realtime.
Algorithm should be:
- ret = guest-set-time()
- if (ret = success)
- rtc-reset-reinjection()
That leaves a window where RTC interrupts are reinjected, but i
see no better option.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2014-06-02 9:13 ` [Qemu-devel] [patch 0/2] add QMP command to reset rtc interrupt backlog Michal Privoznik
2014-06-02 16:31 ` Marcelo Tosatti
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