linux-kernel - [tip:perfcounters/core] perf_counter, x86: return raw count with x86_perf_counter

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Date:	Wed, 29 Apr 2009 13:08:02 GMT
From:	tip-bot for Robert Richter <robert.richter@....com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, robert.richter@....com, a.p.zijlstra@...llo.nl,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter, x86: return raw count with x86_perf_counter_update()

Commit-ID:  4b7bfd0d276da3a006d37e85d3cf900d7a14ae2a
Gitweb:     http://git.kernel.org/tip/4b7bfd0d276da3a006d37e85d3cf900d7a14ae2a
Author:     Robert Richter <robert.richter@....com>
AuthorDate: Wed, 29 Apr 2009 12:47:22 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 29 Apr 2009 14:51:13 +0200

perf_counter, x86: return raw count with x86_perf_counter_update()

To check on AMD cpus if a counter overflows, the upper bit of the raw
counter value must be checked. This value is already internally
available in x86_perf_counter_update(). Now, the value is returned so
that it can be used directly to check for overflows.

[ Impact: micro-optimization ]

Signed-off-by: Robert Richter <robert.richter@....com>
Cc: Paul Mackerras <paulus@...ba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1241002046-8832-26-git-send-email-robert.richter@....com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/kernel/cpu/perf_counter.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index f4d59d4..a8a53ab 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -132,7 +132,7 @@ static u64 amd_pmu_raw_event(u64 event)
  * Can only be executed on the CPU where the counter is active.
  * Returns the delta events processed.
  */
-static void
+static u64
 x86_perf_counter_update(struct perf_counter *counter,
 			struct hw_perf_counter *hwc, int idx)
 {
@@ -165,6 +165,8 @@ again:
 
 	atomic64_add(delta, &counter->count);
 	atomic64_sub(delta, &hwc->period_left);
+
+	return new_raw_count;
 }
 
 static atomic_t num_counters;
@@ -785,8 +787,7 @@ static int amd_pmu_handle_irq(struct pt_regs *regs, int nmi)
 			continue;
 		counter = cpuc->counters[idx];
 		hwc = &counter->hw;
-		x86_perf_counter_update(counter, hwc, idx);
-		val = atomic64_read(&hwc->prev_count);
+		val = x86_perf_counter_update(counter, hwc, idx);
 		if (val & (1ULL << (x86_pmu.counter_bits - 1)))
 			continue;
 		/* counter overflow */
--
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