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Subject[tip:perfcounters/core] perf_counter: counter overflow limit
Commit-ID:  79f146415623fe74f39af67c0f6adc208939a410
Gitweb: http://git.kernel.org/tip/79f146415623fe74f39af67c0f6adc208939a410
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Mon, 6 Apr 2009 11:45:07 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 7 Apr 2009 10:48:58 +0200

perf_counter: counter overflow limit

Provide means to auto-disable the counter after 'n' overflow events.

Create the counter with hw_event.disabled = 1, and then issue an
ioctl(fd, PREF_COUNTER_IOC_REFRESH, n); to set the limit and enable
the counter.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094518.083139737@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
include/linux/perf_counter.h | 12 +++++++--
kernel/perf_counter.c | 51 +++++++++++++++++++++++++++++++++--------
2 files changed, 50 insertions(+), 13 deletions(-)
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 928a7fa..ef4dcbf 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -155,8 +155,9 @@ struct perf_counter_hw_event {
/*
* Ioctls that can be done on a perf counter fd:
*/
-#define PERF_COUNTER_IOC_ENABLE _IO('$', 0)
-#define PERF_COUNTER_IOC_DISABLE _IO('$', 1)
+#define PERF_COUNTER_IOC_ENABLE _IO ('$', 0)
+#define PERF_COUNTER_IOC_DISABLE _IO ('$', 1)
+#define PERF_COUNTER_IOC_REFRESH _IOW('$', 2, u32)

/*
* Structure of the page that can be mapped via mmap
@@ -403,9 +404,14 @@ struct perf_counter {
/* poll related */
wait_queue_head_t waitq;
struct fasync_struct *fasync;
- /* optional: for NMIs */
+
+ /* delayed work for NMIs and such */
+ int pending_wakeup;
+ int pending_disable;
struct perf_pending_entry pending;

+ atomic_t event_limit;
+
void (*destroy)(struct perf_counter *);
struct rcu_head rcu_head;
#endif
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 19990d1..c05e103 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -744,6 +744,12 @@ static void perf_counter_enable(struct perf_counter *counter)
spin_unlock_irq(&ctx->lock);
}

+static void perf_counter_refresh(struct perf_counter *counter, int refresh)
+{
+ atomic_add(refresh, &counter->event_limit);
+ perf_counter_enable(counter);
+}
+
/*
* Enable a counter and all its children.
*/
@@ -1311,6 +1317,9 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
case PERF_COUNTER_IOC_DISABLE:
perf_counter_disable_family(counter);
break;
+ case PERF_COUNTER_IOC_REFRESH:
+ perf_counter_refresh(counter, arg);
+ break;
default:
err = -ENOTTY;
}
@@ -1590,14 +1599,6 @@ void perf_counter_wakeup(struct perf_counter *counter)
kill_fasync(&counter->fasync, SIGIO, POLL_IN);
}

-static void perf_pending_wakeup(struct perf_pending_entry *entry)
-{
- struct perf_counter *counter = container_of(entry,
- struct perf_counter, pending);
-
- perf_counter_wakeup(counter);
-}
-
/*
* Pending wakeups
*
@@ -1607,6 +1608,22 @@ static void perf_pending_wakeup(struct perf_pending_entry *entry)
* single linked list and use cmpxchg() to add entries lockless.
*/

+static void perf_pending_counter(struct perf_pending_entry *entry)
+{
+ struct perf_counter *counter = container_of(entry,
+ struct perf_counter, pending);
+
+ if (counter->pending_disable) {
+ counter->pending_disable = 0;
+ perf_counter_disable(counter);
+ }
+
+ if (counter->pending_wakeup) {
+ counter->pending_wakeup = 0;
+ perf_counter_wakeup(counter);
+ }
+}
+
#define PENDING_TAIL ((struct perf_pending_entry *)-1UL)

static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
@@ -1715,8 +1732,9 @@ struct perf_output_handle {
static inline void __perf_output_wakeup(struct perf_output_handle *handle)
{
if (handle->nmi) {
+ handle->counter->pending_wakeup = 1;
perf_pending_queue(&handle->counter->pending,
- perf_pending_wakeup);
+ perf_pending_counter);
} else
perf_counter_wakeup(handle->counter);
}
@@ -2063,8 +2081,21 @@ void perf_counter_munmap(unsigned long addr, unsigned long len,
int perf_counter_overflow(struct perf_counter *counter,
int nmi, struct pt_regs *regs)
{
+ int events = atomic_read(&counter->event_limit);
+ int ret = 0;
+
+ if (events && atomic_dec_and_test(&counter->event_limit)) {
+ ret = 1;
+ if (nmi) {
+ counter->pending_disable = 1;
+ perf_pending_queue(&counter->pending,
+ perf_pending_counter);
+ } else
+ perf_counter_disable(counter);
+ }
+
perf_counter_output(counter, nmi, regs);
- return 0;
+ return ret;
}

/*

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