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perf/aux: Make aux_{head,wakeup} ring_buffer members long

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The aux_head and aux_wakeup members of struct ring_buffer are defined
using the local_t type, despite the fact that they are only accessed via
the perf_aux_output_*() functions, which cannot race with each other for a
given ring buffer.

This patch changes the type of the members to long, so we can avoid
using the local_*() API where it isn't needed.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1502900297-21839-1-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Will Deacon 2017-08-16 17:18:16 +01:00 committed by Ingo Molnar
parent 290d9bf281
commit 2ab346cfb0
2 changed files with 16 additions and 19 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
kernel/events/internal.h
View file

@ -38,9 +38,9 @@ struct ring_buffer {
struct user_struct *mmap_user;
/* AUX area */
local_t aux_head;
long aux_head;
local_t aux_nest;
local_t aux_wakeup;
long aux_wakeup;
unsigned long aux_pgoff;
int aux_nr_pages;
int aux_overwrite;

31
kernel/events/ring_buffer.c
View file

@ -367,7 +367,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1)))
goto err_put;
aux_head = local_read(&rb->aux_head);
aux_head = rb->aux_head;
handle->rb = rb;
handle->event = event;
@ -382,7 +382,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
*/
if (!rb->aux_overwrite) {
aux_tail = ACCESS_ONCE(rb->user_page->aux_tail);
handle->wakeup = local_read(&rb->aux_wakeup) + rb->aux_watermark;
handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
if (aux_head - aux_tail < perf_aux_size(rb))
handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));
@ -433,12 +433,12 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
handle->aux_flags |= PERF_AUX_FLAG_OVERWRITE;
aux_head = handle->head;
local_set(&rb->aux_head, aux_head);
rb->aux_head = aux_head;
} else {
handle->aux_flags &= ~PERF_AUX_FLAG_OVERWRITE;
aux_head = local_read(&rb->aux_head);
local_add(size, &rb->aux_head);
aux_head = rb->aux_head;
rb->aux_head += size;
}
if (size || handle->aux_flags) {
@ -450,11 +450,10 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
handle->aux_flags);
}
aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
rb->user_page->aux_head = rb->aux_head;
if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
wakeup = true;
local_add(rb->aux_watermark, &rb->aux_wakeup);
rb->aux_wakeup += rb->aux_watermark;
}
if (wakeup) {
@ -478,22 +477,20 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
{
struct ring_buffer *rb = handle->rb;
unsigned long aux_head;
if (size > handle->size)
return -ENOSPC;
local_add(size, &rb->aux_head);
rb->aux_head += size;
aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
rb->user_page->aux_head = rb->aux_head;
if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
perf_output_wakeup(handle);
local_add(rb->aux_watermark, &rb->aux_wakeup);
handle->wakeup = local_read(&rb->aux_wakeup) +
rb->aux_watermark;
rb->aux_wakeup += rb->aux_watermark;
handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
}
handle->head = aux_head;
handle->head = rb->aux_head;
handle->size -= size;
return 0;