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perf_counter: uncouple data_head updates from wakeups 

Keep data_head up-to-date irrespective of notifications. This fixes
the case where you disable a counter and don't get a notification for
the last few pending events, and it also allows polling usage.

[ Impact: increase precision of perfcounter mmap-ed fields ]

Suggested-by: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20090505155436.925084300@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-05-05 17:50:22 +02:00 committed by Ingo Molnar
parent 066d7dea32
commit c66de4a5be
2 changed files with 12 additions and 12 deletions
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4
include/linux/perf_counter.h
View File

@ -362,9 +362,11 @@ struct perf_mmap_data {
atomic_t head; /* write position */
atomic_t events; /* event limit */
atomic_t wakeup_head; /* completed head */
atomic_t done_head; /* completed head */
atomic_t lock; /* concurrent writes */
atomic_t wakeup; /* needs a wakeup */
struct perf_counter_mmap_page *user_page;
void *data_pages[0];
};

20
kernel/perf_counter.c
View File

@ -1696,7 +1696,6 @@ struct perf_output_handle {
struct perf_mmap_data *data;
unsigned int offset;
unsigned int head;
int wakeup;
int nmi;
int overflow;
int locked;
@ -1752,8 +1751,7 @@ static void perf_output_unlock(struct perf_output_handle *handle)
struct perf_mmap_data *data = handle->data;
int head, cpu;
if (handle->wakeup)
data->wakeup_head = data->head;
data->done_head = data->head;
if (!handle->locked)
goto out;
@ -1764,13 +1762,11 @@ again:
* before we publish the new head, matched by a rmb() in userspace when
* reading this position.
*/
while ((head = atomic_xchg(&data->wakeup_head, 0))) {
while ((head = atomic_xchg(&data->done_head, 0)))
data->user_page->data_head = head;
handle->wakeup = 1;
}
/*
* NMI can happen here, which means we can miss a wakeup_head update.
* NMI can happen here, which means we can miss a done_head update.
*/
cpu = atomic_xchg(&data->lock, 0);
@ -1779,7 +1775,7 @@ again:
/*
* Therefore we have to validate we did not indeed do so.
*/
if (unlikely(atomic_read(&data->wakeup_head))) {
if (unlikely(atomic_read(&data->done_head))) {
/*
* Since we had it locked, we can lock it again.
*/
@ -1789,7 +1785,7 @@ again:
goto again;
}
if (handle->wakeup)
if (atomic_xchg(&data->wakeup, 0))
perf_output_wakeup(handle);
out:
local_irq_restore(handle->flags);
@ -1824,7 +1820,9 @@ static int perf_output_begin(struct perf_output_handle *handle,
handle->offset = offset;
handle->head = head;
handle->wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT);
if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT))
atomic_set(&data->wakeup, 1);
return 0;
@ -1882,7 +1880,7 @@ static void perf_output_end(struct perf_output_handle *handle)
int events = atomic_inc_return(&data->events);
if (events >= wakeup_events) {
atomic_sub(wakeup_events, &data->events);
handle->wakeup = 1;
atomic_set(&data->wakeup, 1);
}
}