From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754205Ab3HEQ4h (ORCPT ); Mon, 5 Aug 2013 12:56:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36707 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753463Ab3HEQ4g (ORCPT ); Mon, 5 Aug 2013 12:56:36 -0400 Date: Mon, 5 Aug 2013 18:50:34 +0200 From: Oleg Nesterov To: Ingo Molnar Cc: Steven Rostedt , Frederic Weisbecker , Peter Zijlstra , David Ahern , Masami Hiramatsu , "zhangwei(Jovi)" , linux-kernel@vger.kernel.org Subject: [PATCH 0/3] Teach perf_trace_##call() to check hlist_empty(perf_events) Message-ID: <20130805165034.GA6344@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry for double post, forgot to cc lkml... On 07/19, Ingo Molnar wrote: > > * Oleg Nesterov wrote: > > > Hello. > > > > The patches are the same, I only tried to update the changelogs a bit. > > I am also quoting my old email below, to explain what this hack tries > > to do. > > > > Say, "perf record -e sched:sched_switch -p1". > > > > Every task except /sbin/init will do perf_trace_sched_switch() and > > perf_trace_buf_prepare() + perf_trace_buf_submit for no reason(), > > it doesn't have a counter. > > > > So it makes sense to add the fast-path check at the start of > > perf_trace_##call(), > > > > if (hlist_empty(event_call->perf_events)) > > return; > > > > The problem is, we should not do this if __task != NULL (iow, if > > DECLARE_EVENT_CLASS() uses __perf_task()), perf_tp_event() has the > > additional code for this case. > > > > So we should do > > > > if (!__task && hlist_empty(event_call->perf_events)) > > return; > > > > But __task is changed by "{ assign; }" block right before > > perf_trace_buf_submit(). Too late for the fast-path check, > > we already called perf_trace_buf_prepare/fetch_regs. > > > > So. After 2/3 __perf_task() (and __perf_count/addr) is called > > when ftrace_get_offsets_##call(args) evaluates the arguments, > > and we can check !__task && hlist_empty() right after that. > > > > Oleg. > > Nice improvement. > > Peter, Steve, any objections? Ingo, It seems that everybody agree with this hack but it was forgotten, let me resend it again. The only change is that I added the following tags: Tested-by: David Ahern Reviewed-and-Acked-by: Steven Rostedt Oleg. include/trace/events/sched.h | 22 ++++++++-------------- include/trace/ftrace.h | 33 ++++++++++++++++++++------------- 2 files changed, 28 insertions(+), 27 deletions(-)