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Message-ID: <5295AACE.2080606@intel.com>
Date: Wed, 27 Nov 2013 10:18:22 +0200
From: Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki 
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To: Ingo Molnar <mingo@kernel.org>
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
References: <1385471964-4037-1-git-send-email-adrian.hunter@intel.com> <20131126161553.GB7775@gmail.com>
In-Reply-To: <20131126161553.GB7775@gmail.com>
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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