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: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter 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: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 2b5e66d5ebdf0e0397796562fd78d14d38e26c21..48212c15b7d6ba66390e16a9897c67d828961388 100644 (file)
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -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];

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 0dfe91094fd148a3e3f066ceaa70712003fe455c..affe227d56a0490c95a7f16d3f3db0d3302a738d 100644 (file)
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -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;