Response inline. On Thu, Mar 22, 2018 at 12:25 PM Jonathan Rajotte-Julien < jonathan.rajotte-jul...@efficios.com> wrote:
> Hi Alok, > > On Thu, Mar 22, 2018 at 06:31:41PM +0000, Alok Priyadarshi wrote: > > I am trying to collect a trace for visualizing callstack using > > lttng_ust_cyg_profile. > > > > Even though I have compiled a single source file with > > -finstrument-functions, I guess it is producing too many events to > > considerably slow down the instrumented process and cause lost events. > > Did you have a look at [1]. A "fast" shared object is available. > > [1] https://lttng.org/man/3/lttng-ust-cyg-profile/v2.10/ Yes - I tried both - fast and regular. I did not notice any difference. > > > > > I am using clang, which does not support > > -finstrument-functions-exclude-file-list. > > Might want to give gcc a chance then. > The version of gcc I am using has a bug which produces linker errors for intrinsics when compiled with -finstrument-functions. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78333 I will either need to find a gcc version where this bug is fixed or figure out a workaround. Using clang seemed easier, but then it does not support -finstrument-functions-exclude-file-list :| > > Is there any way to > > filter lttng_ust_cyg_profile events before they are written to the > trace? I > > have tried various things: > > 1. lttng-track to only track one process > > > > 2. Only enable lttng_ust_cyg_profile:* events > > > > 3. Increase the subbuffer size: > > lttng enable-channel --userspace --buffers-pid --subbuf-size=2M > > --num-subbuf=2 mychannel > > Is there any reason you are using --buffer-pid instead of the default > per-uid buffering? > No particular reason. I read somewhere in the mailing list that --buffer-pid might be less susceptible to lose events. I can switch back to using the default per-uid buffering if that is better for my usecase. > > Using this option is very flaky however. It crashes lttng-sessiond. > > > > We will need the log (lttng-sessiond -vvv) (pastebin) and the version of > lttng for this. > OK. I will get you that when I back at work. > Does your workflow looks somewhat similar to this? > > 1) Instrumented app is started with relevant LD_PRELOAD > 2) lttng create my_session > 3) lttng enable-channel -u --subbuf-size=2M --num-subbuf=8 my_channel > 4) lttng enable-event -u -c my_channel 'lttng_ust_cyg_profile:*' > 5) lttng track -u -p <PID> > 6) lttng start > ... some time pass > 7) lttng stop > 8) lttng destroy > > If a discarded events warning is reported the solution is to increase > either the > size or the number of subbuffers per cpu. Note that the upper limit for > the total > subbuffers size is dictated by the available free memory of the system. > Yup - exactly. Except I am using --num-subbuf=2. I have also tried --subbuf-size as 4M and 8M, without much success. > > Any other ideas to filter events? > > > > I am also open to explicitly adding tracepoints to the functions I care > > about. But I am not sure how they can be visualized in trace-compass > > callstack view. > > Neither am I, this might be a better question for the tracecompass mailing > list. > OK. I will ping the tracecompass mailing list. Is there any tool that can just show events on each thread timeline? I have a multi-threaded application, and I want to just visualize when functions enter/exit on various thread with respect to each other. Using lttng_ust_cyg_profile seemed straightforward, but apparently not. Thanks for your help Jonathan.
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