poll: avoid extra wakeups in select/poll
After introduction of keyed wakeups Davide Libenzi did on epoll, we are
able to avoid spurious wakeups in poll()/select() code too.
For example, typical use of poll()/select() is to wait for incoming
network frames on many sockets. But TX completion for UDP/TCP frames call
sock_wfree() which in turn schedules thread.
When scheduled, thread does a full scan of all polled fds and can sleep
again, because nothing is really available. If number of fds is large,
this cause significant load.
This patch makes select()/poll() aware of keyed wakeups and useless
wakeups are avoided. This reduces number of context switches by about 50%
on some setups, and work performed by sofirq handlers.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 8c24ef8..fa287f2 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -32,6 +32,7 @@
typedef struct poll_table_struct {
poll_queue_proc qproc;
+ unsigned long key;
} poll_table;
static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
@@ -43,10 +44,12 @@
static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc)
{
pt->qproc = qproc;
+ pt->key = ~0UL; /* all events enabled */
}
struct poll_table_entry {
struct file *filp;
+ unsigned long key;
wait_queue_t wait;
wait_queue_head_t *wait_address;
};