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perf_counter: more elaborate write API

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Provide a begin, copy, end interface to the output buffer.

begin() reserves the space,
 copy() copies the data over, considering page boundaries,
  end() finalizes the event and does the wakeup.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Orig-LKML-Reference: <20090325113316.740550870@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-03-25 12:30:22 +01:00 committed by Ingo Molnar
parent c7138f37f9
commit b9cacc7bf1
1 changed files with 80 additions and 39 deletions
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119
kernel/perf_counter.c
View file

@ -9,6 +9,7 @@
*/
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/file.h>
@ -16,15 +17,14 @@
#include <linux/sysfs.h>
#include <linux/ptrace.h>
#include <linux/percpu.h>
#include <linux/vmstat.h>
#include <linux/hardirq.h>
#include <linux/rculist.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/anon_inodes.h>
#include <linux/kernel_stat.h>
#include <linux/perf_counter.h>
#include <linux/mm.h>
#include <linux/vmstat.h>
#include <linux/rculist.h>
#include <linux/hardirq.h>
#include <asm/irq_regs.h>
@ -1411,16 +1411,20 @@ static const struct file_operations perf_fops = {
* Output
*/
static int perf_output_write(struct perf_counter *counter, int nmi,
void *buf, ssize_t size)
struct perf_output_handle {
struct perf_counter *counter;
struct perf_mmap_data *data;
unsigned int offset;
int wakeup;
};
static int perf_output_begin(struct perf_output_handle *handle,
struct perf_counter *counter, unsigned int size)
{
struct perf_mmap_data *data;
unsigned int offset, head, nr;
unsigned int len;
int ret, wakeup;
unsigned int offset, head;
rcu_read_lock();
ret = -ENOSPC;
data = rcu_dereference(counter->data);
if (!data)
goto out;
@ -1428,45 +1432,82 @@ static int perf_output_write(struct perf_counter *counter, int nmi,
if (!data->nr_pages)
goto out;
ret = -EINVAL;
if (size > PAGE_SIZE)
goto out;
do {
offset = head = atomic_read(&data->head);
head += size;
} while (atomic_cmpxchg(&data->head, offset, head) != offset);
wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT);
handle->counter = counter;
handle->data = data;
handle->offset = offset;
handle->wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT);
nr = (offset >> PAGE_SHIFT) & (data->nr_pages - 1);
offset &= PAGE_SIZE - 1;
return 0;
len = min_t(unsigned int, PAGE_SIZE - offset, size);
memcpy(data->data_pages[nr] + offset, buf, len);
size -= len;
if (size) {
nr = (nr + 1) & (data->nr_pages - 1);
memcpy(data->data_pages[nr], buf + len, size);
}
/*
* generate a poll() wakeup for every page boundary crossed
*/
if (wakeup) {
atomic_xchg(&data->wakeup, POLL_IN);
__perf_counter_update_userpage(counter, data);
if (nmi) {
counter->wakeup_pending = 1;
set_perf_counter_pending();
} else
wake_up(&counter->waitq);
}
ret = 0;
out:
rcu_read_unlock();
return -ENOSPC;
}
static void perf_output_copy(struct perf_output_handle *handle,
void *buf, unsigned int len)
{
unsigned int pages_mask;
unsigned int offset;
unsigned int size;
void **pages;
offset = handle->offset;
pages_mask = handle->data->nr_pages - 1;
pages = handle->data->data_pages;
do {
unsigned int page_offset;
int nr;
nr = (offset >> PAGE_SHIFT) & pages_mask;
page_offset = offset & (PAGE_SIZE - 1);
size = min_t(unsigned int, PAGE_SIZE - page_offset, len);
memcpy(pages[nr] + page_offset, buf, size);
len -= size;
buf += size;
offset += size;
} while (len);
handle->offset = offset;
}
static void perf_output_end(struct perf_output_handle *handle, int nmi)
{
if (handle->wakeup) {
(void)atomic_xchg(&handle->data->wakeup, POLL_IN);
__perf_counter_update_userpage(handle->counter, handle->data);
if (nmi) {
handle->counter->wakeup_pending = 1;
set_perf_counter_pending();
} else
wake_up(&handle->counter->waitq);
}
rcu_read_unlock();
}
static int perf_output_write(struct perf_counter *counter, int nmi,
void *buf, ssize_t size)
{
struct perf_output_handle handle;
int ret;
ret = perf_output_begin(&handle, counter, size);
if (ret)
goto out;
perf_output_copy(&handle, buf, size);
perf_output_end(&handle, nmi);
out:
return ret;
}