perf session: Add comment for perf_session__register_idle_thread() (b25756df) · Commits · e / devices / android_kernel_fairphone_FP5

Add a comment to perf_session__register_idle_thread() to bring attention to a pitfall with the idle task thread structure. The pitfall is that there should really be a 'struct thread' for the idle task of each cpu, but there is only one that can have pid == tid == 0. Signed-off-by:

Adrian Hunter <adrian.hunter@intel.com> Acked-by:

Jiri Olsa <jolsa@kernel.org> Link: http://lkml.kernel.org/r/20181221120620.9659-9-adrian.hunter@intel.com Signed-off-by:

Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/session.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -1527,6 +1527,13 @@ struct thread perf_session__findnew(struct perf_session session, pid_t pid)
		return machine__findnew_thread(&session->machines.host, -1, pid);
		}

		/*
		* Threads are identified by pid and tid, and the idle task has pid == tid == 0.
		* So here a single thread is created for that, but actually there is a separate
		* idle task per cpu, so there should be one 'struct thread' per cpu, but there
		* is only 1. That causes problems for some tools, requiring workarounds. For
		* example get_idle_thread() in builtin-sched.c, or thread_stack__per_cpu().
		*/
		int perf_session__register_idle_thread(struct perf_session *session)
		{
		struct thread *thread;