linux-kernel - Re: [PATCH 13/15] perf_counter: provide generic callchain bits

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Message-Id: <1238654631.8530.5361.camel@twins>
Date:	Thu, 02 Apr 2009 08:43:51 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/15] perf_counter: provide generic callchain bits

On Wed, 2009-04-01 at 16:25 -0700, Corey Ashford wrote:

> > struct callchain_event {
> > 	u64 nr
> > 	u64 ips[nr]
> > };
> 
> Looking at the current version of perf_counter.h in the -tip tree, this 
> struct definition is not visible to userspace (it's in the #ifdef KERNEL 
> section).

Correct. Its been on my todo list to write a meta-struct definition
along with the perf_event_type enum that details the data layout of the
various types, but not include any actual structure other than the
header in the userspace bits.

Also, related to a comment Paul made on callchain markers, I wanted to
change it so that we have ip markers in the chain that separate the
kernel and user bits.

I was thinking of ending the kernel trace with -1ULL and ending the user
chain with 0ULL. Presumably we need one more to end hypervisor chains in
case anybody manages to generate those ;-).

This chain however will not change the struct, it will merely add 2
extra entries.

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