linux-kernel - Re: [patch] perf

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Date:	Thu, 09 Jul 2009 15:24:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vince@...ter.net>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] perf_counter: Add p6 PMU

On Thu, 2009-07-09 at 00:14 +0200, Peter Zijlstra wrote: 
> On Wed, 2009-07-08 at 23:45 +0200, Peter Zijlstra wrote:
> > On Wed, 2009-07-08 at 17:46 -0400, Vince Weaver wrote:
> > > On Wed, 8 Jul 2009, Peter Zijlstra wrote:
> > > 
> > > >   doesn't sound like the right kind of event.. but then, it doesn't
> > > >   have anything better either.
> > > 
> > > Is there a way to specify "invalid event"?  Just setting it to 0 doesn't 
> > > work, on the Pentium Pro event 0 returns what looks like essentially
> > > random numbers.
> > 
> > Hmm, bugger. I was assuming writing 0 to the evensel would disable the
> > counter. Apparently that only works for eventsel1, which would mean we
> > cannot run counter1 without counter0. That means we'd need to do a
> > counter swap at times... :/
> 
> Ooh, we can instead use a counter that's specified to not count anything
> for 'disabling' the counter, like event 0x2E with unit mask 0.

The below seems to work..

--- 
arch/x86/kernel/cpu/perf_counter.c |   28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

Index: linux-2.6/arch/x86/kernel/cpu/perf_counter.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_counter.c
+++ linux-2.6/arch/x86/kernel/cpu/perf_counter.c
@@ -84,6 +84,14 @@ static u64 p6_pmu_event_map(int event)
 	return p6_perfmon_event_map[event];
 }
 
+/*
+ * Counter setting that is specified not to count anything.
+ * We use this to effectively disable a counter.
+ *
+ * L2_RQSTS with 0 MESI unit mask.
+ */
+#define P6_NOP_COUNTER			0x0000002EULL
+
 static u64 p6_pmu_raw_event(u64 event)
 {
 #define P6_EVNTSEL_EVENT_MASK		0x000000FFULL
@@ -704,6 +712,7 @@ static int __hw_perf_counter_init(struct
 {
 	struct perf_counter_attr *attr = &counter->attr;
 	struct hw_perf_counter *hwc = &counter->hw;
+	u64 config;
 	int err;
 
 	if (!x86_pmu_initialized())
@@ -756,10 +765,19 @@ static int __hw_perf_counter_init(struct
 
 	if (attr->config >= x86_pmu.max_events)
 		return -EINVAL;
+
 	/*
 	 * The generic map:
 	 */
-	hwc->config |= x86_pmu.event_map(attr->config);
+	config = x86_pmu.event_map(attr->config);
+
+	if (config == 0)
+		return -ENOENT;
+
+	if (config == -1LL)
+		return -EINVAL;
+
+	hwc->config |= config;
 
 	return 0;
 }
@@ -767,7 +785,7 @@ static int __hw_perf_counter_init(struct
 static void p6_pmu_disable_all(void)
 {
 	struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
-	unsigned long val;
+	u64 val;
 
 	if (!cpuc->enabled)
 		return;
@@ -917,10 +935,10 @@ static inline void
 p6_pmu_disable_counter(struct hw_perf_counter *hwc, int idx)
 {
 	struct cpu_hw_counters *cpuc = &__get_cpu_var(cpu_hw_counters);
-	unsigned long val = ARCH_PERFMON_EVENTSEL0_ENABLE;
+	u64 val = P6_NOP_COUNTER;
 
-	if (!cpuc->enabled)
-		val = 0;
+	if (cpuc->enabled)
+		val |= ARCH_PERFMON_EVENTSEL0_ENABLE;
 
 	(void)checking_wrmsrl(hwc->config_base + idx, val);
 }

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