linux-kernel - RE: ptrace API extensions for BTS

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Message-ID: <029E5BE7F699594398CA44E3DDF55444014A581D@swsmsx413.ger.corp.intel.com>
Date:	Wed, 30 Jan 2008 12:52:40 -0000
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	"stephane eranian" <eranian@...glemail.com>
Cc:	"Roland McGrath" <roland@...hat.com>,
	"Ingo Molnar" <mingo@...e.hu>, <linux-kernel@...r.kernel.org>,
	<markus.t.metzger@...il.com>
Subject: RE: ptrace API extensions for BTS

>From: stephane eranian [mailto:eranian@...glemail.com] 
>Sent: Mittwoch, 30. Januar 2008 12:01

>You can get information about the perfmon2 project at: 
>http://perfmon2.sf.net

I downloaded your patch for 2.6.23 and cloned your git repository.

>From a first glance, it looks like there is indeed a lot of overlap.

>I would like to take a look at your patches. Where can I get them?

You can find the changes in the mm branch of the x86 git. Do they keep
the patches there, somewhere, as well?

You should get the best overview if you look at arch/x86/kernel/ds.c,
include/asm-x86/ds.h, include/asm-x86/ptrace-abi.h, and
arch/x86/kernel/ptrace.c or simply grep for BTS.

I have all the patches that I submitted but they rather protocol
development than describe the final thing.

>My understanding at this point is that we would need to coordinate
>access to the
>DS_AREA. It would likely have to be mutually exclusive access. 

>From a brief look at your patch, I would say that we should rather
combine the configuration and collection part. They are very similar.

We might still want to provide different interfaces on top of it.
In particular, I think the ptrace interface is most appropriate for
debuggers.

>I am planning on
>adding support for LBRs in the next few months. But BTS the way it is
>currently defined
>is useless for performance monitoring. I think this a great debug
>feature, though.

Debugging was my target;-)

>Now, there is some preliminary perf. MSR allocator in the kernel.
>However, it does not know
>of all available MSRs out there. It focuses on the counters mostly.
>Perfmon, oprofile and
>the NMI watchdog use it. I think it could be generalized to other MSR
>(non-contiguous).
>
>I would be happy to work with you in refining this MSR allocator.

Are you planning to get the perfmon patch into the kernel? Or do you
want it to remain a separate patch?

In the first case, we should try to merge the features. In the second
case, refining the MSR allocator would probably be best.

thanks and regards,
markus.
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