X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=doc%2Fman%2Flttng.1;h=3a358dd78ff21d919a8dd1d6760f5b2ca33866ca;hp=99941db93af0d0a5d4436c91bbe230c7d67e70ac;hb=2201988389cd5f7df8c41948302792e50d5bb52a;hpb=3ae6f6665030769040c46549ce4b4c9117ee09f6 diff --git a/doc/man/lttng.1 b/doc/man/lttng.1 index 99941db93..3a358dd78 100644 --- a/doc/man/lttng.1 +++ b/doc/man/lttng.1 @@ -82,9 +82,9 @@ Simple listing of lttng options. Simple listing of lttng commands. .SH "COMMANDS" -.TP +.PP \fBadd-context\fP -.nf +.RS Add context to event(s) and/or channel(s). A context is basically extra information appended to a channel. For instance, @@ -96,7 +96,10 @@ For example, this command will add the context information 'prio' and two perf counters (hardware branch misses and cache misses), to all events in the trace data output: -# lttng add-context \-k \-t prio \-t perf:branch-misses \-t perf:cache-misses +.nf +# lttng add-context \-k \-t prio \-t perf:branch-misses \\ + \-t perf:cache-misses +.fi Please take a look at the help (\-h/\-\-help) for a detailed list of available contexts. @@ -107,30 +110,34 @@ Otherwise the context will be added only to the given channel (\-c). If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc file. -.fi .B OPTIONS: -.nf -\-h, \-\-help - Show summary of possible options and commands. -\-s, \-\-session NAME - Apply on session name. -\-c, \-\-channel NAME - Apply on channel name. -\-k, \-\-kernel - Apply for the kernel tracer -\-u, \-\-userspace - Apply for the user-space tracer -\-t, \-\-type TYPE - Context type. You can repeat this option on the command line. Please - use "lttng add-context \-h" to list all available types. -.fi - -.IP +.TP +.BR "\-h, \-\-help" +Show summary of possible options and commands. +.TP +.BR "\-s, \-\-session NAME" +Apply on session name. +.TP +.BR "\-c, \-\-channel NAME" +Apply on channel name. +.TP +.BR "\-k, \-\-kernel" +Apply for the kernel tracer +.TP +.BR "\-u, \-\-userspace" +Apply for the user-space tracer +.TP +.BR "\-t, \-\-type TYPE" +Context type. You can repeat this option on the command line. Please +use "lttng add-context \-h" to list all available types. +.RE +.PP -.IP "\fBcalibrate\fP" -.nf +.PP +\fBcalibrate\fP [OPTIONS] +.RS Quantify LTTng overhead The LTTng calibrate command can be used to find out the combined average @@ -152,16 +159,21 @@ an empty function, gathering PMU counters LLC (Last Level Cache) misses information (see lttng add-context \-\-help to see the list of available PMU counters). +.nf # lttng create calibrate-function -# lttng enable-event calibrate \-\-kernel \-\-function lttng_calibrate_kretprobe -# lttng add-context \-\-kernel \-t perf:LLC-load-misses \-t perf:LLC-store-misses \\ - \-t perf:LLC-prefetch-misses +# lttng enable-event calibrate \-\-kernel \\ + \-\-function lttng_calibrate_kretprobe +# lttng add-context \-\-kernel \-t perf:LLC-load-misses \\ + \-t perf:LLC-store-misses \\ + \-t perf:LLC-prefetch-misses # lttng start # for a in $(seq 1 10); do \\ lttng calibrate \-\-kernel \-\-function; done # lttng destroy -# babeltrace $(ls \-1drt ~/lttng-traces/calibrate-function-* | tail \-n 1) +# babeltrace $(ls \-1drt ~/lttng-traces/calibrate-function-* \\ + | tail \-n 1) +.fi The output from babeltrace can be saved to a text file and opened in a spreadsheet (e.g. oocalc) to focus on the per-PMU counter delta between @@ -172,10 +184,12 @@ staying on the same CPU must be considered. The average result, for the i7, on 10 samples: +.nf Average Std.Dev. perf_LLC_load_misses: 5.0 0.577 perf_LLC_store_misses: 1.6 0.516 perf_LLC_prefetch_misses: 9.0 14.742 +.fi As we can notice, the load and store misses are relatively stable across runs (their standard deviation is relatively low) compared to the prefetch misses. @@ -183,22 +197,23 @@ We can conclude from this information that LLC load and store misses can be accounted for quite precisely, but prefetches within a function seems to behave too erratically (not much causality link between the code executed and the CPU prefetch activity) to be accounted for. -.fi .B OPTIONS: -.nf -\-h, \-\-help - Show summary of possible options and commands. -\-k, \-\-kernel - Apply for the kernel tracer -\-u, \-\-userspace - Apply for the user-space tracer -\-\-function - Dynamic function entry/return probe (default) -.fi - -.IP +.TP +.BR "\-h, \-\-help" +Show summary of possible options and commands. +.TP +.BR "\-k, \-\-kernel" +Apply for the kernel tracer +.TP +.BR "\-u, \-\-userspace" +Apply for the user-space tracer +.TP +.BR "\-\-function" +Dynamic function entry/return probe (default) +.RE +.PP .IP "\fBcreate\fP [NAME] [OPTIONS] .nf @@ -230,6 +245,13 @@ a non-writeable home directory. Simple listing of options \-o, \-\-output PATH Specify output path for traces +\-\-no-output + Traces will not be outputed +\-\-snapshot + Set the session in snapshot mode. Created in no-output mode + and uses the URL, if one, as the default snapshot output. + Every channel will be set in overwrite mode and with mmap + output (splice not supported). Using these options, each API call can be controlled individually. For instance, \-C does not enable the consumer automatically. You'll need the \-e