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perf: Optimize the hotpath by converting the perf output buffer to local_t

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Since there is now only a single writer, we can use
local_t instead and avoid all these pesky LOCK insn.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2010-05-18 10:54:20 +02:00 committed by Ingo Molnar
parent ef60777c9a
commit fa5881514e
2 changed files with 22 additions and 23 deletions
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15
include/linux/perf_event.h
View file

@ -485,6 +485,7 @@ struct perf_guest_info_callbacks {
#include <linux/ftrace.h>
#include <linux/cpu.h>
#include <asm/atomic.h>
#include <asm/local.h>
#define PERF_MAX_STACK_DEPTH 255
@ -588,20 +589,18 @@ struct perf_mmap_data {
#ifdef CONFIG_PERF_USE_VMALLOC
struct work_struct work;
#endif
int data_order;
int data_order; /* allocation order */
int nr_pages; /* nr of data pages */
int writable; /* are we writable */
int nr_locked; /* nr pages mlocked */
atomic_t poll; /* POLL_ for wakeups */
atomic_t events; /* event_id limit */
atomic_long_t head; /* write position */
atomic_t wakeup; /* needs a wakeup */
atomic_t lost; /* nr records lost */
atomic_t nest; /* nested writers */
local_t head; /* write position */
local_t nest; /* nested writers */
local_t events; /* event limit */
local_t wakeup; /* needs a wakeup */
local_t lost; /* nr records lost */
long watermark; /* wakeup watermark */

30
kernel/perf_event.c
View file

@ -2916,7 +2916,7 @@ static void perf_output_get_handle(struct perf_output_handle *handle)
struct perf_mmap_data *data = handle->data;
preempt_disable();
atomic_inc(&data->nest);
local_inc(&data->nest);
}
static void perf_output_put_handle(struct perf_output_handle *handle)
@ -2925,13 +2925,13 @@ static void perf_output_put_handle(struct perf_output_handle *handle)
unsigned long head;
again:
head = atomic_long_read(&data->head);
head = local_read(&data->head);
/*
* IRQ/NMI can happen here, which means we can miss a head update.
*/
if (!atomic_dec_and_test(&data->nest))
if (!local_dec_and_test(&data->nest))
return;
/*
@ -2945,12 +2945,12 @@ again:
* Now check if we missed an update, rely on the (compiler)
* barrier in atomic_dec_and_test() to re-read data->head.
*/
if (unlikely(head != atomic_long_read(&data->head))) {
atomic_inc(&data->nest);
if (unlikely(head != local_read(&data->head))) {
local_inc(&data->nest);
goto again;
}
if (atomic_xchg(&data->wakeup, 0))
if (local_xchg(&data->wakeup, 0))
perf_output_wakeup(handle);
preempt_enable();
@ -3031,7 +3031,7 @@ int perf_output_begin(struct perf_output_handle *handle,
if (!data->nr_pages)
goto out;
have_lost = atomic_read(&data->lost);
have_lost = local_read(&data->lost);
if (have_lost)
size += sizeof(lost_event);
@ -3045,24 +3045,24 @@ int perf_output_begin(struct perf_output_handle *handle,
*/
tail = ACCESS_ONCE(data->user_page->data_tail);
smp_rmb();
offset = head = atomic_long_read(&data->head);
offset = head = local_read(&data->head);
head += size;
if (unlikely(!perf_output_space(data, tail, offset, head)))
goto fail;
} while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
} while (local_cmpxchg(&data->head, offset, head) != offset);
handle->offset = offset;
handle->head = head;
if (head - tail > data->watermark)
atomic_inc(&data->wakeup);
local_inc(&data->wakeup);
if (have_lost) {
lost_event.header.type = PERF_RECORD_LOST;
lost_event.header.misc = 0;
lost_event.header.size = sizeof(lost_event);
lost_event.id = event->id;
lost_event.lost = atomic_xchg(&data->lost, 0);
lost_event.lost = local_xchg(&data->lost, 0);
perf_output_put(handle, lost_event);
}
@ -3070,7 +3070,7 @@ int perf_output_begin(struct perf_output_handle *handle,
return 0;
fail:
atomic_inc(&data->lost);
local_inc(&data->lost);
perf_output_put_handle(handle);
out:
rcu_read_unlock();
@ -3086,10 +3086,10 @@ void perf_output_end(struct perf_output_handle *handle)
int wakeup_events = event->attr.wakeup_events;
if (handle->sample && wakeup_events) {
int events = atomic_inc_return(&data->events);
int events = local_inc_return(&data->events);
if (events >= wakeup_events) {
atomic_sub(wakeup_events, &data->events);
atomic_inc(&data->wakeup);
local_sub(wakeup_events, &data->events);
local_inc(&data->wakeup);
}
}