From: Oleg Nesterov Date: Tue, 6 Aug 2013 16:08:47 +0000 (+0200) Subject: tracing/perf: Avoid perf_trace_buf_*() in perf_trace_##call() when possible X-Git-Tag: v3.12-rc1~168^3~15^2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d027e6a9c83440bf1ca9e5503539d58d8e0914f1;p=pandora-kernel.git tracing/perf: Avoid perf_trace_buf_*() in perf_trace_##call() when possible perf_trace_buf_prepare() + perf_trace_buf_submit(task => NULL) make no sense if hlist_empty(head). Change perf_trace_##call() to check ->perf_events beforehand and do nothing if it is empty. This removes the overhead for tasks without events associated with them. For example, "perf record -e sched:sched_switch -p1" attaches the counter(s) to the single task, but every task in system will do perf_trace_buf_prepare/submit() just to realize that it was not attached to this event. However, we can only do this if __task == NULL, so we also add the __builtin_constant_p(__task) check. With this patch "perf bench sched pipe" shows approximately 4% improvement when "perf record -p1" runs in parallel, many thanks to Steven for the testing. Link: http://lkml.kernel.org/r/20130806160847.GA2746@redhat.com Tested-by: David Ahern Acked-by: Peter Zijlstra Signed-off-by: Oleg Nesterov Signed-off-by: Steven Rostedt --- Reading git-diff-tree failed