Re: xentrace, xenalyze

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Wed, 2016-02-24 at 15:21 +0200, Paul Sujkov wrote:
> Hi,
> 
Hi,

> I'm from GlobalLogic team that uses Xen as a base for an automative
> platform. Got few questions regarding Xen tracing and it seems that
> existing documentation is rather limited.
> 
It is...

> At the previous Xen Hackathon I was talking about shared (mediated
> pass-through) GPU concept for ARM; it's working well, but still has
> performance issues, and some of them seem to be correlated to other
> Xen subsystems, but it's not obvious why so (e.g. turning off pv real
> time clock driver gives us a significant boost in overall graphics
> performance). So, I'm looking for two things here actually:
> 
Great to hear you're (still) working on this. I'm looking forward to
see the results! :-D

> 1. to understand how can I use xenalyze to find bottlenecks in the
> system at the moment
>
This is hard to tell (at least with such a broad scope).

xentrace supports quite a bit of events, but enabling all of them may
may not be what you want. For one, it would produce traces that are so
big and complex to analyze, that it would be very hard to make sense
out of them.

I usually enable a subset of them (one or more "classes") and try to
figure out if I see the problem in the resulting trace. If yes, I try
with a narrower subset. If not, I try with either a broader or a
different one.

> 2. to add VGPU scheduler traces to Xen trace subsystem, xenbaked,
> xentrace and xenalyze
> 
I've never used xenbaked. I've only used xentrace_format and xenalyze.
I don't know if xenbaked still works/can still be useful.

> Some insights into the second question can be found in RTDS scheduler
> patches (it adds a few of it's own trace events and uses generic
> scheduler tracing); however, it uses already functioning scheduler
> tracing subsystem which is VCPU specific and is not suitable for
> VGPU, and there are no visible patches to xenalyze to parse these
> traces out.
> 
Have a look at this series:
 http://lists.xenproject.org/archives/html/xen-devel/2016-02/msg02233.html

And I've got another one that I'll send out asap (and I can Cc you).

There are for sure some examples of adding trace points in Xen, and
adding support for them in xentrace_format and xenalyze.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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