linux-kernel - [PATCH] powerpc: perf: Fix frequency calculation for overflowing counters (FSL version)

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Date:	Tue, 18 Jan 2011 21:44:04 +1100
From:	Anton Blanchard <anton@...ba.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Scott Wood <scottwood@...escale.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH] powerpc: perf: Fix frequency calculation for overflowing
 counters (FSL version)


> > Does perf_event_fsl_emb.c need this as well (it has almost the same
> > record_and_restart code)? 
> 
> I would think so.

Good point:


When fixing the frequency calculations for perf on powerpc I forgot
to fix the FSL version.

If we dont set event->hw.last_period the frequency to period calculations
in perf go haywire and we continually throttle/unthrottle the PMU.

Signed-off-by: Anton Blanchard <anton@...ba.org>
---

This is only compile tested.

Index: powerpc.git/arch/powerpc/kernel/perf_event_fsl_emb.c
===================================================================
--- powerpc.git.orig/arch/powerpc/kernel/perf_event_fsl_emb.c	2011-01-18 21:23:57.761644115 +1100
+++ powerpc.git/arch/powerpc/kernel/perf_event_fsl_emb.c	2011-01-18 21:25:28.994477247 +1100
@@ -596,6 +596,7 @@ static void record_and_restart(struct pe
 			if (left <= 0)
 				left = period;
 			record = 1;
+			event->hw.last_period = event->hw.sample_period;
 		}
 		if (left < 0x80000000LL)
 			val = 0x80000000LL - left;


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