Accuracy of traces sync [Was: Re: [PATCH] Fix `make -jN trace-cmd gui`]

From: Dario Faggioli <dfaggioli@suse.com>
To: "Yordan Karadzhov (VMware)" <y.karadz@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-devel@vger.kernel.org
Subject: Accuracy of traces sync [Was: Re: [PATCH] Fix `make -jN trace-cmd gui`]
Date: Fri, 20 Nov 2020 14:43:21 +0100	[thread overview]
Message-ID: <849f846631f3014c3eff7f37a7d61493e2af66a9.camel@suse.com> (raw)
In-Reply-To: <02672da2-8b62-a573-786d-1cb8f5970e85@gmail.com>

[-- Attachment #1: Type: text/plain, Size: 2004 bytes --]

On Fri, 2020-11-20 at 14:32 +0200, Yordan Karadzhov (VMware) wrote:
> On 20.11.20 г. 14:06 ч., Dario Faggioli wrote:
> > > 
> > Yep, sure! I followed the talks you've been giving about it at
> > events, and I even played a little with what you have here:
> > 
> > https://github.com/yordan-karadzhov/kernel-shark-2.alpha
> > 
> > The host-guest tracing part, as I think you can guess.
> 
> Ciao Dario,
>
Hey!

> I am very happy to hear that. The timestamp synchronization patches
> for 
> trace-cmd are almost ready to go upstream.
> 
Yes, I tried those patches!

In fact, now that I have you here, do you mind if I change the subject
and ask a quick question about them?

So, you often say that "the accuracy of the synchronization protocol is
XX ms". Now, I guess that means that an event in the guest and the
corresponding event in the host (or vice versa) are XX ms apart. And
that's even after the synchronization of the two traces, is that right?

Question is, how do you measure that? Sure, I can look manually for an
occurrence of the pattern that I described above: i.e., an event in the
guest, then the corresponding one in the host and compute the
difference between the timestamps.

But do you have a way to do so automatically, or with a script/program,
etc?

I saw that the series included a patch which was meant at debugging and
profiling PTP, but even with that one applied and having it generate
the graphs, I have not been able to get that info without manual
inspection.

> And we are currently reviewing a beta version of KernelShark_2 that
> will 
> include the guest/host visualization.
> As Steven said: stay tuned!
> 
You bet I will. :-P

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
-------------------------------------------------------------------
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]