linux-kernel - Re: [GIT PULL 0/2] perf annotate fix and report improvoment

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Message-ID: <AANLkTimOEUKYXzdMOiWE6gRxR7vJX36VscdLjRroqGLq@mail.gmail.com>
Date:	Wed, 26 May 2010 21:07:05 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	mingo@...e.hu, Peter Zijlstra <peterz@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [GIT PULL 0/2] perf annotate fix and report improvoment

Hi,

+lkml et al.

On Wed, May 26, 2010 at 8:23 PM, Arnaldo Carvalho de Melo
<acme@...radead.org> wrote:
> Em Wed, May 26, 2010 at 06:45:18PM +0200, Stephane Eranian escreveu:
>> Attached is the trace for
>> perf annotate -i ~/perf.data noploop
>>
>> I get no output at all (TUI is off). Copied over .debug tarball + perf.data.
>
> Looks like the bug I'm investigating now:
>
> build id event received for [kernel.kallsyms]: 54b1e7cc3cf52e0db255aab44ce7538eb62655b8
> build id event received for /tmp/noploop: 875ae61623e89f408b425ca0486a9ec99e3ac73e
> Looking at the vmlinux_path (5 entries long)
> No build_id in vmlinux, ignoring it
> No build_id in /boot/vmlinux, ignoring it
> No build_id in /boot/vmlinux-2.6.34-tip-default+, ignoring it
> build_id in /lib/modules/2.6.34-tip-default+/build/vmlinux is
> 3635a0e8dfc9a1afbd5627c2ba789e41d77d3cd1 while expected is
> 54b1e7cc3cf52e0db255aab44ce7538eb62655b8, ignoring it
> No build_id in /usr/lib/debug/lib/modules/2.6.34-tip-default+/vmlinux, ignoring it
>
> In my case it is not finding the vmlinux because I'm using RHEL6 Beta
> kernel without the respective kernel-debuginfo{-common} packages so it
> doesn't find the vmlinux, uses just /proc/kallsyms and that is not
> enough for annotation.
>
> In your case the problem is that we only cache the kallsyms file in the
> build-id cache ($HOME/.debug) and that is not enough for annotation, so
> I have to fix two things:
>
I can understand the issue with the kernel symbols.
But in this example, I only really care about the symbols in the
noploop program (/tmp/noploop).

Missing symbol support for the kernel should not cause perf to avoid
trying to resolve the symbols in other modules such as my user program
here.

> 1. tell about these constraints when a symbol cannot be annotated, not
> just silently fail
>
Agreed, print something like <uknown symbol> or <cannot resolve symbol>


> 2. cache the vmlinux file in the build-id cache instead of the vmlinux,
> if the vmlinux file was found, if not, fallback to caching the kallsyms
> file.
>
Don't you need to match buildid here too, the vmlinux linux on the host
may not match the one on the target, i.e., monitored system.

> Both can't be cached at the same time as they will have the same
> build-id and thus at least the symlink would be to one of them.
>
> I'll make this even configurable in ~/.perfconfig, on a new [symbol]
> section, something like:
>
> [symbol]
>
>        cache_vmlinux = on/off
>
> So that people that have issues with the size of these beasts can trade
> off disk space used by the cache versus being able to do annotation.
>
Yes, disk space is an issue.
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