Commit c7138f37 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf_counter: fix perf_poll() 



Impact: fix kerneltop 100% CPU usage

Only return a poll event when there's actually been one, poll_wait()
doesn't actually wait for the waitq you pass it, it only enqueues
you on it.

Only once all FDs have been iterated and none of thm returned a
poll-event will it schedule().

Also make it return POLL_HUP when there's not mmap() area to read from.

Further, fix a silly bug in the write code.

Reported-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Orig-LKML-Reference: <1237897096.24918.181.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent f66c6b20

include/linux/perf_counter.h

+1 −0
Original line number Diff line number Diff line
@@ -246,6 +246,7 @@ struct file; 
struct perf_mmap_data {

	struct rcu_head			rcu_head;

	int				nr_pages;

	atomic_t			wakeup;

	atomic_t			head;

	struct perf_counter_mmap_page   *user_page;

	void 				*data_pages[0];

kernel/perf_counter.c

+12 −2
Original line number Diff line number Diff line
@@ -1161,7 +1161,16 @@ perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) 
static unsigned int perf_poll(struct file *file, poll_table *wait)

{

	struct perf_counter *counter = file->private_data;

	unsigned int events = POLLIN;

	struct perf_mmap_data *data;

	unsigned int events;



	rcu_read_lock();

	data = rcu_dereference(counter->data);

	if (data)

		events = atomic_xchg(&data->wakeup, 0);

	else

		events = POLL_HUP;

	rcu_read_unlock();



	poll_wait(file, &counter->waitq, wait);
@@ -1425,7 +1434,7 @@ static int perf_output_write(struct perf_counter *counter, int nmi, 


	do {

		offset = head = atomic_read(&data->head);

		head += sizeof(u64);

		head += size;

	} while (atomic_cmpxchg(&data->head, offset, head) != offset);



	wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT);
@@ -1446,6 +1455,7 @@ static int perf_output_write(struct perf_counter *counter, int nmi, 
	 * 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;

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