Re: Instructions for clock sync for tracing host/guest

[Joel Fernandes <joelaf@google.com>]

On Fri, Apr 23, 2021 at 7:33 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> Hi Joel,
>
> FYI, VMware gave everyone the day off today, so don't expect any real
> responses till next week.

Got it.

> On Fri, 23 Apr 2021 04:37:40 -0400
> Joel Fernandes <joelaf@google.com> wrote:
>
> > Apologies for the top post as I'm on Gmail mobile and only half awake at
> > 4.30am.  I should check but can we just scrape the crosvm PIDs from the
> > host trace itself ? The vCPU threads are in scheduler events in the host
> > trace. Of course that wouldn't work if we don't have events. Let me know if
> > that works for you or if I should find another way.
> >
> > By the way if sync is supposed to fall back to the ptp algo, why did it not
> > fallback for me?
>
> If both guest and host support an algo, it will use the one that has the
> best synchronization (like KVM). If the guest says it supports KVM and the
> host says it supports KVM, then it will use it. The question now remains,
> did one of them lie? ;-)

Good question, will try to debug and see what each said.

> > Other thoughts:
> > - it would be cool if trace cmd agent was run by the host directly on the
> > guest. That might eliminate a step. I can try to see if that's possible
> > with crosvm but it's not super high priority.
>
> Not sure what you mean by that.

I meant that currently, doing "trace-cmd agent" in the guest is an
extra step. I'd rather the "trace-cmd record" on the host spawn the
agent within the guest somehow, thus eliminating that extra step.

> > Yes thanks for sending me any patches and happy to try.
>
> Feel free to send us patches too! ;-)

Yes, certainly. My first attempt was to see if I could hit the ground
running with my VM problems, if trace-cmd was in sufficient shape.
Looks like trace-cmd is almost there and happy to help with the best
of my ability to write any patches.

> Anyway, see you next week.

You too, thanks,
-Joel

>
> -- Steve