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Date: Thu, 4 Feb 2010 09:57:28 GMT
From: tip-bot for Stephane Eranian <eranian@...gle.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, acme@...hat.com, paulus@...ba.org,
eranian@...gle.com, hpa@...or.com, mingo@...hat.com,
a.p.zijlstra@...llo.nl, efault@....de, fweisbec@...il.com,
tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perf/core] perf_events, x86: Fix bug in hw_perf_enable()
Commit-ID: 447a194b393f32699607fd99617a40abd6a95114
Gitweb: http://git.kernel.org/tip/447a194b393f32699607fd99617a40abd6a95114
Author: Stephane Eranian <eranian@...gle.com>
AuthorDate: Mon, 1 Feb 2010 14:50:01 +0200
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Thu, 4 Feb 2010 09:59:50 +0100
perf_events, x86: Fix bug in hw_perf_enable()
We cannot assume that because hwc->idx == assign[i], we can avoid
reprogramming the counter in hw_perf_enable().
The event may have been scheduled out and another event may have been
programmed into this counter. Thus, we need a more robust way of
verifying if the counter still contains config/data related to an event.
This patch adds a generation number to each counter on each cpu. Using
this mechanism we can verify reliabilty whether the content of a counter
corresponds to an event.
Signed-off-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Mike Galbraith <efault@....de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
LKML-Reference: <4b66dc67.0b38560a.1635.ffffae18@...google.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
arch/x86/kernel/cpu/perf_event.c | 34 ++++++++++++++++++++++++++++------
include/linux/perf_event.h | 2 ++
2 files changed, 30 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 96cfc1a..a920f17 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -90,6 +90,7 @@ struct cpu_hw_events {
int n_events;
int n_added;
int assign[X86_PMC_IDX_MAX]; /* event to counter assignment */
+ u64 tags[X86_PMC_IDX_MAX];
struct perf_event *event_list[X86_PMC_IDX_MAX]; /* in enabled order */
};
@@ -1142,6 +1143,8 @@ static int __hw_perf_event_init(struct perf_event *event)
hwc->config = ARCH_PERFMON_EVENTSEL_INT;
hwc->idx = -1;
+ hwc->last_cpu = -1;
+ hwc->last_tag = ~0ULL;
/*
* Count user and OS events unless requested not to.
@@ -1457,11 +1460,14 @@ static int collect_events(struct cpu_hw_events *cpuc, struct perf_event *leader,
return n;
}
-
static inline void x86_assign_hw_event(struct perf_event *event,
- struct hw_perf_event *hwc, int idx)
+ struct cpu_hw_events *cpuc, int i)
{
- hwc->idx = idx;
+ struct hw_perf_event *hwc = &event->hw;
+
+ hwc->idx = cpuc->assign[i];
+ hwc->last_cpu = smp_processor_id();
+ hwc->last_tag = ++cpuc->tags[i];
if (hwc->idx == X86_PMC_IDX_FIXED_BTS) {
hwc->config_base = 0;
@@ -1480,6 +1486,15 @@ static inline void x86_assign_hw_event(struct perf_event *event,
}
}
+static inline int match_prev_assignment(struct hw_perf_event *hwc,
+ struct cpu_hw_events *cpuc,
+ int i)
+{
+ return hwc->idx == cpuc->assign[i] &&
+ hwc->last_cpu == smp_processor_id() &&
+ hwc->last_tag == cpuc->tags[i];
+}
+
static void __x86_pmu_disable(struct perf_event *event, struct cpu_hw_events *cpuc);
void hw_perf_enable(void)
@@ -1508,7 +1523,14 @@ void hw_perf_enable(void)
event = cpuc->event_list[i];
hwc = &event->hw;
- if (hwc->idx == -1 || hwc->idx == cpuc->assign[i])
+ /*
+ * we can avoid reprogramming counter if:
+ * - assigned same counter as last time
+ * - running on same CPU as last time
+ * - no other event has used the counter since
+ */
+ if (hwc->idx == -1 ||
+ match_prev_assignment(hwc, cpuc, i))
continue;
__x86_pmu_disable(event, cpuc);
@@ -1522,12 +1544,12 @@ void hw_perf_enable(void)
hwc = &event->hw;
if (hwc->idx == -1) {
- x86_assign_hw_event(event, hwc, cpuc->assign[i]);
+ x86_assign_hw_event(event, cpuc, i);
x86_perf_event_set_period(event, hwc, hwc->idx);
}
/*
* need to mark as active because x86_pmu_disable()
- * clear active_mask and eventsp[] yet it preserves
+ * clear active_mask and events[] yet it preserves
* idx
*/
set_bit(hwc->idx, cpuc->active_mask);
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 556b0f4..071a7db 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -478,9 +478,11 @@ struct hw_perf_event {
union {
struct { /* hardware */
u64 config;
+ u64 last_tag;
unsigned long config_base;
unsigned long event_base;
int idx;
+ int last_cpu;
};
struct { /* software */
s64 remaining;
--
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