Last time I checked, the main issue with perf's handling of cases that lack frame pointers is that they grab a ~2-4kB worth of stack data into the trace, and then post-process it with libunwind. This might be OK for sampling use-cases, but is not something I consider appropriate for tracing due to considerably increased use of tracing throughput.
Has the situation changed on the perf side ? Thanks, Mathieu ----- On Mar 27, 2020, at 9:44 AM, Valentin Grigorev <valentin.grigo...@jetbrains.com> wrote: > Yeah, as far as I know, perf [1] is successfully using libunwind to provide > callstacks. Probably, LTTng team should think about it too, if there are no > serious obstacles. > [1]: [ https://perf.wiki.kernel.org/index.php/Main_Page | > https://perf.wiki.kernel.org/index.php/Main_Page ] > Best regards, > Valentin Grigorev > On Thu, Mar 26, 2020 at 11:53 PM Milian Wolff < [ > mailto:milian.wo...@kdab.com | > milian.wo...@kdab.com ] > wrote: >> On Donnerstag, 26. März 2020 20:41:17 CET Mathieu Desnoyers via lttng-dev >> wrote: >>> ----- On Mar 26, 2020, at 1:39 PM, lttng-dev < [ >> > mailto:lttng-dev@lists.lttng.org | lttng-dev@lists.lttng.org ] > >> wrote: >> > > Hello! >> > > Currently, callstack collection in LTTng is only available for >> > > kernel-space >> > > events with context fields callstack-kernel and callstack-user . >> > > Is it expected that callstack collection for LTTng-UST will be added too? >> > > And if it is expected, then how soon? >> > Hi Valentin, >> > It is something that would be interesting and useful, but a lot of work >> > would be needed to have stack-walking this is fast enough and reentrant wrt >> > signal handlers. Unfortunately, the backtrace(3) functions do not meet >> > those requirements. >> > Also, for gathering user-space callstacks from the kernel tracer, it only >> > works if all user-space is compiled with frame pointers. This is also a >> > limitation that would require a lot of work to overcome neatly. >> > None of those features are currently on any roadmap due to lack of >> > customers >> > showing interest in getting this done. >> libunwind [1] should meet the requirements you need. It is high performance >> thanks to extensive caching, signal safe and does not rely on frame pointers. >> [1]: [ https://github.com/libunwind/libunwind | >> https://github.com/libunwind/libunwind ] >> -- >> Milian Wolff | [ mailto:milian.wo...@kdab.com | milian.wo...@kdab.com ] | >> Senior >> Software Engineer >> KDAB (Deutschland) GmbH, a KDAB Group company >> Tel: +49-30-521325470 >> KDAB - The Qt, C++ and OpenGL Experts -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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