Re: Instructions for clock sync for tracing host/guest

[Tzvetomir Stoyanov <tz.stoyanov@xxxxxxxxx>]

On Mon, Apr 26, 2021 at 3:44 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Mon, 26 Apr 2021 13:58:18 +0300
> Tzvetomir Stoyanov <tz.stoyanov@xxxxxxxxx> wrote:
>
> > On Fri, Apr 23, 2021 at 11:37 AM Joel Fernandes <joelaf@xxxxxxxxxx> 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?
> >
> > Because of a bug in the code. It assumes if KVM is detected, then qemu
> > is used to run the VMs.
> >
>
> We need to find a way to do this without qemu. It's only the thread mapping
> that is missing here, nothing else. And KVM sync should still work.

The problem is to find the VM specific directory in the KVM debugfs,
where the VM TSC parameters are. The name of the directory is
/sys/kernel/debug/kvm/<some PID>-<number>/
The PID is the qemu process which runs the VM. I wonder how it looks in crosvm ?

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--
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center