From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valentin Grigorev via lttng-dev Subject: Re: LTTng user-space callstacks Date: Fri, 27 Mar 2020 16:44:19 +0300 Message-ID: References: <2022773652.13655.1585251677207.JavaMail.zimbra@efficios.com> <1834419.usQuhbGJ8B@agathebauer> Reply-To: Valentin Grigorev Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============6153713742388908343==" Return-path: Received: from mail-oi1-x243.google.com (mail-oi1-x243.google.com [IPv6:2607:f8b0:4864:20::243]) by lists.lttng.org (Postfix) with ESMTPS id 48pjl84ZSwz1W27 for ; Fri, 27 Mar 2020 09:44:36 -0400 (EDT) Received: by mail-oi1-x243.google.com with SMTP id p125so8746369oif.10 for ; Fri, 27 Mar 2020 06:44:36 -0700 (PDT) In-Reply-To: <1834419.usQuhbGJ8B@agathebauer> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" To: Milian Wolff Cc: lttng-dev List-Id: lttng-dev@lists.lttng.org --===============6153713742388908343== Content-Type: multipart/alternative; boundary="0000000000004cfc4d05a1d64d0c" --0000000000004cfc4d05a1d64d0c Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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 Best regards, Valentin Grigorev On Thu, Mar 26, 2020 at 11:53 PM Milian Wolff wrote= : > On Donnerstag, 26. M=C3=A4rz 2020 20:41:17 CET Mathieu Desnoyers via lttn= g-dev > wrote: > > ----- On Mar 26, 2020, at 1:39 PM, lttng-dev > > 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 on= ly > > 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 > > -- > Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer > KDAB (Deutschland) GmbH, a KDAB Group company > Tel: +49-30-521325470 > KDAB - The Qt, C++ and OpenGL Experts --0000000000004cfc4d05a1d64d0c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Yeah, as far=C2=A0as I know, perf [1= ] is successfully using libunwind to provide callstacks. Probably, LTTng te= am should think about it too, if there are no serious obstacles.
=


<= div>
Best regards,
Valentin Grigorev


On Thu, Mar 26, 2020 at 11:53 PM Milian Wolff <milian.wolff@kdab.com> wrote:
On= Donnerstag, 26. M=C3=A4rz 2020 20:41:17 CET Mathieu Desnoyers via lttng-de= v
wrote:
> ----- On Mar 26, 2020, at 1:39 PM, lttng-dev <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 .<= br> > >
> > Is it expected that callstack collection for LTTng-UST will be ad= ded too?
> > And if it is expected, then how soon?
>
> Hi Valentin,
>
> It is something that would be interesting and useful, but a lot of wor= k
> would be needed to have stack-walking this is fast enough and reentran= t wrt
> signal handlers. Unfortunately, the backtrace(3) functions do not meet=
> those requirements.
>
> Also, for gathering user-space callstacks from the kernel tracer, it o= nly
> 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 cus= tomers
> 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 pointer= s.

[1]: https://github.com/libunwind/libunwind

--
Milian Wolff | m= ilian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt, C++ and OpenGL Experts
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