linux-kernel - Re: [PATCH 3/4] perf_counter: frequency based adaptive irq

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Message-Id: <1242394667.6642.1887.camel@laptop>
Date:	Fri, 15 May 2009 15:37:47 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] perf_counter: frequency based adaptive irq_period

On Fri, 2009-05-15 at 15:19 +0200, Peter Zijlstra wrote:
> plain text document attachment (perf_counter-freq.patch)
> Instead of specifying the irq_period for a counter, provide a target interrupt
> frequency and dynamically adapt the irq_period to match this frequency.
> 
> Paul, please verify ppc64, I only did a very quick pass over that code.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> CC: Paul Mackerras <paulus@...ba.org>
> CC: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
> ---

> @@ -2907,6 +2940,12 @@ perf_counter_alloc(struct perf_counter_h
>  
>  	pmu = NULL;
>  
> +	hwc = &counter->hw;
> +	if (hw_event->freq && hw_event->irq_freq)
> +		hwc->irq_period = TICK_NSEC / hw_event->irq_freq;
> +	else
> +		hwc->irq_period = hw_event->irq_period;
> +



kernel/built-in.o: In function `perf_counter_alloc':
perf_counter.c:(.text+0x7ddc7): undefined reference to `__udivdi3'

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---

Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -2942,7 +2942,7 @@ perf_counter_alloc(struct perf_counter_h
 
 	hwc = &counter->hw;
 	if (hw_event->freq && hw_event->irq_freq)
-		hwc->irq_period = TICK_NSEC / hw_event->irq_freq;
+		hwc->irq_period = div64_u64(TICK_NSEC, hw_event->irq_freq);
 	else
 		hwc->irq_period = hw_event->irq_period;
 


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