X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=doc%2Fman%2Flttng-ust.3;h=398498913f104e6456bb87abedf38b7fc7f12e84;hb=7b250cea4c3fd5acbbd36d599fa87caee4ff59d1;hp=1d1197f4672b18af258e29e48a8c0311a9f2940c;hpb=aacb37743add6586531f42c5fc2c6551bf7ffd71;p=lttng-ust.git diff --git a/doc/man/lttng-ust.3 b/doc/man/lttng-ust.3 index 1d1197f4..39849891 100644 --- a/doc/man/lttng-ust.3 +++ b/doc/man/lttng-ust.3 @@ -29,11 +29,11 @@ tracef() API. To do it, in a nutshell: 3) Link your program against liblttng-ust.so. -4) Enable the UST debug loglevel when tracing with the following - sequence of commands from lttng-tools: +4) Enable UST events when tracing with the following sequence of commands + from lttng-tools: lttng create - lttng enable-event -u -a --loglevel=TRACE_DEBUG + lttng enable-event -u -a lttng start [... run your program ...] lttng stop @@ -48,6 +48,41 @@ whereas tracepoint.h is meant for thorough instrumentation of a code base to be integrated with an upstream project. .PP +.SH "USAGE WITH TRACELOG" +.PP +If you want to migrate existing logging (info, errors, ...) +to LTTng UST, you can use the tracelog() interface. +To do it, in a nutshell: + +1) #include + +2) /* in your code, use like a printf, with extra loglevel info. */ + tracelog(TRACE_INFO, "Message with integer %d", 1234); + +3) Link your program against liblttng-ust.so. + +4) Enable UST events when tracing with the following sequence of commands + from lttng-tools: + + lttng create + lttng enable-event -u "lttng_ust_tracelog:*" + lttng start + [... run your program ...] + lttng stop + lttng view + +That's it! + +You can replace the enable-event line above with a selection of +loglevels, e.g.: + + lttng enable-event -u -a --loglevel TRACE_INFO + +Which will gather all events from TRACE_INFO and more important +loglevels. + +.PP + .SH "USAGE WITH TRACEPOINT" .PP The simple way to generate the lttng-ust tracepoint probes is to use the @@ -92,11 +127,11 @@ TRACEPOINT_EVENT( sample_component, /* - * tracepoint name, same format as sample provider. Does not - * need to be declared before. in this case the name is - * "message" + * tracepoint name, characters permitted follow the same + * constraints as the provider name. The name of this example + * event is "sample_event". */ - message, + sample_event, /* * TP_ARGS macro contains the arguments passed for the tracepoint @@ -265,7 +300,7 @@ debug information. debug information with line-level scope (TRACEPOINT_EVENT default) TRACE_DEBUG 14 - debug-level message (trace_printf default) + debug-level message See lttng(1) for information on how to use LTTng-UST loglevels. @@ -290,6 +325,33 @@ Even though LTTng-UST supports tracepoint() call site duplicates having the same provider and event name, it is recommended to use a provider event name pair only once within the source code to help map events back to their call sites when analyzing the trace. + +Sometimes arguments to the probe are expensive to compute (e.g. +take call stack). To avoid the computation when the tracepoint is +disabled one can use more 'low level' tracepoint_enabled() and +do_tracepoint() macros as following: + + if (tracepoint_enabled(ust_tests_hello, tptest)) { + /* prepare arguments */ + do_tracepoint(ust_tests_hello, tptest, i, netint, values, + text, strlen(text), dbl, flt); + } + +Here do_tracepoint() doesn't contain check if the tracepoint is enabled. +Using tracepoint() in such scenario is dangerous since it also contains +enabled check and thus race condition is possible in the following code +if the tracepoint has been enabled after check in tracepoint_enabled() +but before tracepoint(): + + if (tracepoint_enabled(provider, name)) { /* tracepoint is disabled */ + prepare(args); + } + /* tracepoint is enabled by 'lttng' tool */ + tracepoint(provider, name, args); /* args wasn't prepared properly */ + +Note also that neither tracepoint_enabled() nor do_tracepoint() have +STAP_PROBEV() call so if you need it you should emit this call yourself. + .fi .SH "BUILDING/LINKING THE TRACEPOINT PROVIDER" @@ -299,17 +361,13 @@ There are 2 ways to compile the Tracepoint Provider with the application: either statically or dynamically. Please follow carefully: - 1.1) Compile the Tracepoint provider with the application, either - directly or through a static library (.a): - - Into exactly one object of your application: define + 1) Compile the Tracepoint Provider with the application, either + directly or through a static library (.a): + - Into exactly one object of your application, define "TRACEPOINT_DEFINE" and include the tracepoint provider. - Use "\-I." for the compilation unit containing the tracepoint - provider include (e.g. tp.c). - - Link application with "\-ldl". - - If building the provider directly into the application, - link the application with "\-llttng-ust". - - If building a static library for the provider, link the static - library with "\-llttng-ust". + provider include (e.g., tp.c). + - Link the application with "\-llttng-ust" and "\-ldl". - Include the tracepoint provider header into all C files using the provider. - Examples: @@ -397,13 +455,9 @@ Pthread identifier. Can be used on architectures where pthread_t maps nicely to an unsigned long type. .PP -.SH "BASE ADDRESS STATEDUMP (Experimental feature)" +.SH "BASE ADDRESS STATEDUMP" .PP -Warning: This is an experimental feature known to cause deadlocks when the -traced application uses fork, clone or daemon. Only use it for debugging and -testing. Do NOT use it in production. - If an application that uses liblttng-ust.so becomes part of a session, information about its currently loaded shared objects will be traced to the session at session-enable time. To record this information, the following event @@ -428,7 +482,7 @@ line number lookup are traced by LTTng. .PP .IP "LTTNG_UST_DEBUG" -Activate liblttng-ust debug output. +Activate liblttng-ust debug and error output. .PP .IP "LTTNG_UST_REGISTER_TIMEOUT" The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to @@ -440,8 +494,20 @@ specified in milliseconds. The value 0 means "don't wait". The value recommended for applications with time constraints on the process startup time. .PP -.IP "LTTNG_UST_WITH_EXPERIMENTAL_BADDR_STATEDUMP" -Experimentally allow liblttng-ust to perform a base-address statedump on session-enable. +.IP "LTTNG_UST_WITHOUT_BADDR_STATEDUMP" +Prevent liblttng-ust to perform a base-address statedump on session-enable. +.PP +.IP "LTTNG_UST_GETCPU_PLUGIN" +Used by the getcpu override plugin system. The environment variable +provides the path to the shared object which will act as the getcpu override +plugin. An example can be found in the lttng-ust documentation under +examples/getcpu-override . +.PP +.IP "LTTNG_UST_CLOCK_PLUGIN" +Used by the clock override plugin system. The environment variable +provides the path to the shared object wich will act as the clock override +plugin. An example can be found in the lttng-ust documentation under +doc/examples/clock-override . .PP .SH "SEE ALSO"