Re: [Xen-devel] [RFC][PATCH] Hypervisor profiling using GCOV

[Tej <bewith.tej@xxxxxxxxx>]

On Thu, Feb 19, 2009 at 8:23 PM, George Dunlap
<george.dunlap@xxxxxxxxxxxxx> wrote:
> Tej wrote:
>>>
>>> Does it get us significantly more than the existing xentrace and
>>> xenoprofile
>>> tools? Especially the latter, which already does program-counter tracing
>>> and
>>> generation of stats from that, via the oprofile tool.
>>>
>>
>> thanks for our feedback
>> i agree xenoprofile is advanced proffiling tool in xen since ages, but
>> GCOV could be useful tool to naive tester/programmer on XEN who really
>> don't understand xenoprofile stats....
>>
>
> Don't undersell gcov; its purpose is slightly different from either xentrace
> or xenoprofile.  Xentrace can be used to get information about what paths or
> reasons caused vmexits (as well as just seeing specific patterns that
> happen).  xenoprofile is a relatively low-overhead way of just profiling
> (which unfortuantely doesn't work properly in 32-on-64 mode ATM).   gcov's
> main purpose is to tell you code coverage; profiling is just a side-effect.

>
> I looked at the LTP page about lcov, and it looks like it was pretty useful
> for them.  It has graphical output with the number of times / percentage a
> given path was taken.  It probably is worth porting to Xen for the same
> reason -- to see how well given paths in Xen actually get exercised.
>>
>> e.g If i start with any hypervisor subsystem (scheduler), i will run
>> xm test suite for scheduler and see  what all code is getting affected
>> over a  period of time and proceed with it...
>>
>
> It sounds like the main problem with xenoprofile is that it's hard to set up
> and use ATM: it could use some attention to the code, and some well-worded
> HOWTOs.  The fact that 32-on-64 doesn't work properly (truncates the long
> EIPs) doesn't help. :-)
>
> So I think that it probably would be useful.  Unfortunately, I don't have
> time in the near future to look at either of these (new "xcov"
> functionality, or fixing xenoprofile).  Gianluca's been doing some
> interesting work with testing.  I'll ask him if he's interested in looking
> at it.

thanks for your valuable feedback....
I need some comments from you or Gianluca regarding the basic design
and coding standard, or any other way it can be improved. Patches are
mainly to show the design and approach we have followed to produce
code coverage.

I am planning to change code of lcov to support xen code coverage out
of box rather than changing lcov config file.
any comments on this?


Anyway here are the patches for xen-3.2 and xen-3.1.*
in Xen-3.2 previous linux patches will do.

>
> Thanks for your work though, Tej!

thanks
-tej

>
> -George
>

xen-3.1-gcov-v1.patch
Description: Binary data

xen-3.2.0-gcov-v1.patch
Description: Binary data

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