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author | Eric Dumazet <dada1@cosmosbay.com> | 2009-06-16 15:33:36 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-06-16 19:47:48 -0700 |
commit | 4938d7e0233a455f04507bac81d0886c71529537 (patch) | |
tree | 6e0c6f0e8623ef44270890519f08b98e9db8afee /fs/select.c | |
parent | 02d5341ae53d32681241b27a40397475caef1c83 (diff) | |
download | kernel_samsung_tuna-4938d7e0233a455f04507bac81d0886c71529537.zip kernel_samsung_tuna-4938d7e0233a455f04507bac81d0886c71529537.tar.gz kernel_samsung_tuna-4938d7e0233a455f04507bac81d0886c71529537.tar.bz2 |
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>
Diffstat (limited to 'fs/select.c')
-rw-r--r-- | fs/select.c | 40 |
1 files changed, 36 insertions, 4 deletions
diff --git a/fs/select.c b/fs/select.c index 0fe0e14..d870237 100644 --- a/fs/select.c +++ b/fs/select.c @@ -168,7 +168,7 @@ static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p) return table->entry++; } -static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key) +static int __pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key) { struct poll_wqueues *pwq = wait->private; DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task); @@ -194,6 +194,16 @@ static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key) return default_wake_function(&dummy_wait, mode, sync, key); } +static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key) +{ + struct poll_table_entry *entry; + + entry = container_of(wait, struct poll_table_entry, wait); + if (key && !((unsigned long)key & entry->key)) + return 0; + return __pollwake(wait, mode, sync, key); +} + /* Add a new entry */ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address, poll_table *p) @@ -205,6 +215,7 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address, get_file(filp); entry->filp = filp; entry->wait_address = wait_address; + entry->key = p->key; init_waitqueue_func_entry(&entry->wait, pollwake); entry->wait.private = pwq; add_wait_queue(wait_address, &entry->wait); @@ -362,6 +373,18 @@ get_max: #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR) #define POLLEX_SET (POLLPRI) +static inline void wait_key_set(poll_table *wait, unsigned long in, + unsigned long out, unsigned long bit) +{ + if (wait) { + wait->key = POLLEX_SET; + if (in & bit) + wait->key |= POLLIN_SET; + if (out & bit) + wait->key |= POLLOUT_SET; + } +} + int do_select(int n, fd_set_bits *fds, struct timespec *end_time) { ktime_t expire, *to = NULL; @@ -418,20 +441,25 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) if (file) { f_op = file->f_op; mask = DEFAULT_POLLMASK; - if (f_op && f_op->poll) - mask = (*f_op->poll)(file, retval ? NULL : wait); + if (f_op && f_op->poll) { + wait_key_set(wait, in, out, bit); + mask = (*f_op->poll)(file, wait); + } fput_light(file, fput_needed); if ((mask & POLLIN_SET) && (in & bit)) { res_in |= bit; retval++; + wait = NULL; } if ((mask & POLLOUT_SET) && (out & bit)) { res_out |= bit; retval++; + wait = NULL; } if ((mask & POLLEX_SET) && (ex & bit)) { res_ex |= bit; retval++; + wait = NULL; } } } @@ -685,8 +713,12 @@ static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait) mask = POLLNVAL; if (file != NULL) { mask = DEFAULT_POLLMASK; - if (file->f_op && file->f_op->poll) + if (file->f_op && file->f_op->poll) { + if (pwait) + pwait->key = pollfd->events | + POLLERR | POLLHUP; mask = file->f_op->poll(file, pwait); + } /* Mask out unneeded events. */ mask &= pollfd->events | POLLERR | POLLHUP; fput_light(file, fput_needed); |