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Date: Wed, 27 Nov 2013 12:52:47 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Jiri Olsa <jolsa@redhat.com>,
        Mike Galbraith <efault@gmx.de>, Namhyung Kim <namhyung@gmail.com>,
        Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf tools: Fix not finding kcore in buildid cache
Message-ID: <20131127115247.GA10528@gmail.com>
References: <1385471964-4037-1-git-send-email-adrian.hunter@intel.com>
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 <5295AACE.2080606@intel.com>
 <20131127113248.GB10495@gmail.com>
 <5295DCAD.80802@intel.com>
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* Adrian Hunter <adrian.hunter@intel.com> wrote:

> On 27/11/13 13:32, Ingo Molnar wrote:
> > 
> > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> > 
> >> On 26/11/13 18:15, Ingo Molnar wrote:
> >>>
> >>> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>
> >>>> The logic was not looking in the buildid cache for kcore
> >>>> if the host kernel buildid did not match the recorded
> >>>> kernel buildid.
> >>>
> >>> It would be nice to also include the specific failure mode in the 
> >>> changelog: exactly how can users run into this. That will be more 
> >>> useful to most people reading these changelogs than a more abstract 
> >>> bug description.
> >>
> >> The preconditions for the problem are that kcore is in the buildid
> >> cache and that the running kernel has a different buildid e.g.
> >>
> >> $ perf buildid-list | grep kernel.kallsyms
> >> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> >>
> >> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> >> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> >>
> >>
> >>
> >> Before the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> >>
> >> perf script stopped
> >>
> >>
> >> After the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> >>
> >> perf script stopped
> > 
> > So the result of the patch is that kernel symbols get 
> > resolved/annotated correctly, as expected from the live kcore feature, 
> > right?
> 
> Yes but this is the non-live case i.e. the kernel has changed and we are
> looking at a special copy of kcore that we placed in the buildid cache
> (using "perf buildid-cache -v -k /proc/kcore") when the data was recorded.

Okay.

Thanks,

	Ingo