On 11/12/13 21:37, David Ahern wrote: > On 12/11/13, 5:36 AM, Alexander Shishkin wrote: >> From: Adrian Hunter <adrian.hun...@intel.com> >> >> Add an option to cause a selected event >> to be opened always without a pid when >> configured by perf_evsel__config(). >> >> This is needed when using the sched_switch >> tracepoint to follow object code execution. >> sched_switch occurs before the task >> switch and so it cannot record it in a >> context limited to that task. Note >> that also means that sched_switch is >> useless when capturing data per-thread, >> as is the 'context-switches' software >> event for the same reason. > > This seems like a tailored solution for what is really a generic problem: > you need events to have different attributes -- a mix of system wide, task > based, with or without callchains and other sample options.
Actually in this case it is not the attribute but another parameter of the perf_event_open syscall, namely the pid. The effect of that is that there are potentially fewer file descriptors needed for that event i.e. just 1 per cpu compared with 1 per cpu per thread. This is a generic solution for the case where you want to mix an event that is not tied to a process, with other events that are. If it were the attribute it would be easy because 'attr' is a member of 'struct evsel' so it can simply be changed directly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
