Re: Instructions for clock sync for tracing host/guest

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

On Sun, Apr 25, 2021 at 9:29 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri, 23 Apr 2021 11:16:50 +0300
> Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:
>
> > Currently we collect that information from quemu, is there a way to
> > get it from crosvm ? If yes, a crosvm support can be implemented in
> > trace-cmd. But as I said, it is not mandatory to have it for the
> > trace, I can send you a patch next week addressing this gap in the
> > implementation.
>
> I think we should be able to get the above information during the KVM
> timesync logic. The host can enable KVM events (specifically
> kvm_entry), and that should give use the pids.
>
>  # trace-cmd record -e kvm_entry ssh guest taskset -c 0 ls \; taskset -c 1 cat /etc/passwd
>  # trace-cmd report
> [..]
>            <...>-129042 [004]1122452427093922: kvm_entry:            vcpu 0
>            <...>-129043 [005]1122452427148178: kvm_entry:            vcpu 1
>            <...>-129042 [004]1122452427150380: kvm_entry:            vcpu 0
>            <...>-129043 [005]1122452427201498: kvm_entry:            vcpu 1
>
> There, I see the guest vcpu 0 is controlled by the host thread with pid
> 129042 and vcpu 1 is controlled by host thread pid 129043.

It works only in case of one VM, if there are more than one - cannot
map kvm_entry event to specific VM.

>
> -- Steve



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