linux-kernel - Re: [PATCH v2 2/3] perf unwind: fix libunwind when tid != pid

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Message-ID: <20190815141035.GJ30356@krava>
Date:   Thu, 15 Aug 2019 16:10:35 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Keeping <john@...anate.com>
Cc:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] perf unwind: fix libunwind when tid != pid

On Thu, Aug 15, 2019 at 11:01:45AM +0100, John Keeping wrote:
> Commit e5adfc3e7e77 ("perf map: Synthesize maps only for thread group
> leader") changed the recording side so that we no longer get mmap events
> for threads other than the thread group leader (when synthesising these
> events for threads which exist before perf is started).
> 
> When a file recorded after this change is loaded, the lack of mmap
> records mean that unwinding is not set up for any other threads.
> 
> This can be seen in a simple record/report scenario:
> 
> 	perf record --call-graph=dwarf -t $TID
> 	perf report
> 
> If $TID is a process ID then the report will show call graphs, but if
> $TID is a secondary thread the output is as if --call-graph=none was
> specified.

great, mucch clearler now

> 
> Following the rationale in that commit, move the libunwind fields into
> struct map_groups and update the libunwind functions to take this
> instead of the struct thread.  This is only required for
> unwind__finish_access which must now be called from map_groups__delete
> and the others are changed for symmetry.
> 
> Note that unwind__get_entries keeps the thread argument since it is
> required for symbol lookup and the libdw unwind provider uses the thread
> ID.
> 
> Fixes: e5adfc3e7e77 ("perf map: Synthesize maps only for thread group leader")

for all 3 patches

Reviewed-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka