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Message-ID: <20130709080513.GG25631@dyad.programming.kicks-ass.net>
Date: Tue, 9 Jul 2013 10:05:14 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Yan, Zheng" <zheng.z.yan@...el.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, eranian@...gle.com,
ak@...ux.intel.com
Subject: Re: [PATCH] perf: Update event buffer tail when overwriting old
events
On Tue, Jul 09, 2013 at 03:05:41PM +0800, Yan, Zheng wrote:
> Thank you for your help. I ran the same test, the results for regular case
> are much better. But it still has about 1% overhead, probably because we
> enlarge the ring_buffer structure, make it less cache friendly.
>
> origin with the patch
> AVG 1000 1013
> STDEV 13.4 15.0
And this is the !overwrite case, right? I don't suppose you cured the logic
Namhyung Kim pointed out? That should affect the overwrite case I suppose since
it won't switch to perf_event_output_overwrite().
tip/master:
struct ring_buffer {
atomic_t refcount; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct callback_head callback_head; /* 8 16 */
int nr_pages; /* 24 4 */
int overwrite; /* 28 4 */
atomic_t poll; /* 32 4 */
/* XXX 4 bytes hole, try to pack */
local_t head; /* 40 8 */
local_t nest; /* 48 8 */
local_t events; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
local_t wakeup; /* 64 8 */
local_t lost; /* 72 8 */
long int watermark; /* 80 8 */
spinlock_t event_lock; /* 88 56 */
/* --- cacheline 2 boundary (128 bytes) was 16 bytes ago --- */
struct list_head event_list; /* 144 16 */
atomic_t mmap_count; /* 160 4 */
/* XXX 4 bytes hole, try to pack */
long unsigned int mmap_locked; /* 168 8 */
struct user_struct * mmap_user; /* 176 8 */
struct perf_event_mmap_page * user_page; /* 184 8 */
/* --- cacheline 3 boundary (192 bytes) --- */
void * data_pages[0]; /* 192 0 */
/* size: 192, cachelines: 3, members: 18 */
/* sum members: 180, holes: 3, sum holes: 12 */
};
tip/master + patch:
struct ring_buffer {
atomic_t refcount; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct callback_head callback_head; /* 8 16 */
int nr_pages; /* 24 4 */
int overwrite; /* 28 4 */
atomic_t poll; /* 32 4 */
/* XXX 4 bytes hole, try to pack */
local_t tail; /* 40 8 */
local_t next_tail; /* 48 8 */
local_t head; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
local_t nest; /* 64 8 */
local_t events; /* 72 8 */
local_t wakeup; /* 80 8 */
local_t lost; /* 88 8 */
long int watermark; /* 96 8 */
spinlock_t event_lock; /* 104 56 */
/* --- cacheline 2 boundary (128 bytes) was 32 bytes ago --- */
struct list_head event_list; /* 160 16 */
atomic_t mmap_count; /* 176 4 */
/* XXX 4 bytes hole, try to pack */
long unsigned int mmap_locked; /* 184 8 */
/* --- cacheline 3 boundary (192 bytes) --- */
struct user_struct * mmap_user; /* 192 8 */
struct perf_event_mmap_page * user_page; /* 200 8 */
void * data_pages[0]; /* 208 0 */
/* size: 208, cachelines: 4, members: 20 */
/* sum members: 196, holes: 3, sum holes: 12 */
/* last cacheline: 16 bytes */
};
tip/master + patch^2:
struct ring_buffer {
atomic_t refcount; /* 0 4 */
atomic_t mmap_count; /* 4 4 */
union {
int overwrite; /* 4 */
struct callback_head callback_head; /* 16 */
}; /* 8 16 */
int nr_pages; /* 24 4 */
atomic_t poll; /* 28 4 */
local_t tail; /* 32 8 */
local_t next_tail; /* 40 8 */
local_t head; /* 48 8 */
local_t nest; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
local_t events; /* 64 8 */
local_t wakeup; /* 72 8 */
local_t lost; /* 80 8 */
long int watermark; /* 88 8 */
spinlock_t event_lock; /* 96 56 */
/* --- cacheline 2 boundary (128 bytes) was 24 bytes ago --- */
struct list_head event_list; /* 152 16 */
long unsigned int mmap_locked; /* 168 8 */
struct user_struct * mmap_user; /* 176 8 */
struct perf_event_mmap_page * user_page; /* 184 8 */
/* --- cacheline 3 boundary (192 bytes) --- */
void * data_pages[0]; /* 192 0 */
/* size: 192, cachelines: 3, members: 19 */
};
---
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4641,7 +4641,7 @@ static void perf_event_output_overwrite(
static void
perf_event_set_overflow(struct perf_event *event, struct ring_buffer *rb)
{
- if (event->overflow_handler != perf_event_output ||
+ if (event->overflow_handler != perf_event_output &&
event->overflow_handler != perf_event_output_overwrite)
return;
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -10,13 +10,16 @@
struct ring_buffer {
atomic_t refcount;
- struct rcu_head rcu_head;
+ atomic_t mmap_count;
+ union {
+ int overwrite; /* can overwrite itself */
+ struct rcu_head rcu_head;
+ };
#ifdef CONFIG_PERF_USE_VMALLOC
struct work_struct work;
int page_order; /* allocation order */
#endif
int nr_pages; /* nr of data pages */
- int overwrite; /* can overwrite itself */
atomic_t poll; /* POLL_ for wakeups */
@@ -33,7 +36,6 @@ struct ring_buffer {
spinlock_t event_lock;
struct list_head event_list;
- atomic_t mmap_count;
unsigned long mmap_locked;
struct user_struct *mmap_user;
--
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