linux-kernel - Re: [RFC][PATCH 0/7] perf trace: general-purpose scripting support, v2

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Date:	Wed, 25 Nov 2009 10:43:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tom Zanussi <tzanussi@...il.com>, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, rostedt@...dmis.org, anton@...ba.org,
	hch@...radead.org, Mike Galbraith <efault@....de>
Subject: Re: [RFC][PATCH 0/7] perf trace: general-purpose scripting support,
 v2


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, 2009-11-25 at 09:28 +0100, Peter Zijlstra wrote:
> > On Wed, 2009-11-25 at 01:15 -0600, Tom Zanussi wrote:
> > > sched::sched_wakeup      0 01238.657997033     6183 firefox              comm=firefox, pid=6199, prio=120, success=1, target_cpu=1
> > > sched::sched_switch      1 01238.657991740     7140 firefox              prev_comm=firefox, prev_pid=7140, prev_prio=120, prev_state=S, next_comm=firefox, next_pid=6199, next_prio=120
> > > 
> > > min_wakeup_latency: -5293 
> > 
> > Looks like we missed a clock update on the cross cpu wakeup, Mike was
> > busy plugging those holes -- I've been starting at a patch that might
> > cure this (amongst other things).
> 
> Hmm, current -tip should have that cured as per:

well, but timestamp inconsistencies are still possible fundamentally, as 
cpu_clock() is not globally serialized.

If so then the (hack only) patch below would cure those timestamp 
inconsistencies?

	Ingo

Not-Signed-off-by-me

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 35df94e..4f36b47 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -248,7 +248,7 @@ static void perf_unpin_context(struct perf_event_context *ctx)
 
 static inline u64 perf_clock(void)
 {
-	return cpu_clock(smp_processor_id());
+	return trace_clock_global();
 }
 
 /*
--
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