Re: Instructions for clock sync for tracing host/guest

[Dario Faggioli <dfaggioli@suse.com>]

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On Mon, 2021-04-26 at 08:56 -0400, Steven Rostedt wrote:
> On Mon, 26 Apr 2021 13:39:32 +0300
> Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:
> > > 
> > > 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.
> 
>  # trace-cmd record -e sched_wakeup -e kvm_entry
> 
> And have this:
> 
>     vsock-client-159876 [000]1346877108580652: sched_wakeup:        
> vhost-128994:129046 [120] success=1 CPU:006
> 
>     vhost-128994-129046 [006]1346877108678708: sched_wakeup:        
> CPU 0/KVM:129042 [120] success=1 CPU:007
> 
>        CPU 0/KVM-129042 [007]1346877109290044: kvm_entry:           
> vcpu 0
> 
Mmm... This is quite interesting. But there's something I don't think
I'm understanding.


> Instead of looking at vsock-client, look at the current pid and see
> what
> "vhost" it wakes up, then see what what thread it wakes up, and then
> see if
> it calls kvm_entry. we don't even need to know if it is a vhost. Just
> trace
> everything that our current thread wakes up and what those wake up
> until
> something calls kvm_entry.
> 
So, what's the mapping (like, mapping between what and what) that we
are interested in here, and what kind of into trick with vsock-client
is helping us gather, that we don't already have by "just" looking at
the kvm_entry events?

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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