From 4938d7e0233a455f04507bac81d0886c71529537 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 16 Jun 2009 15:33:36 -0700 Subject: [PATCH] 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 Acked-by: David S. Miller Acked-by: Andi Kleen Acked-by: Ingo Molnar Acked-by: Davide Libenzi Cc: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/select.c | 40 ++++++++++++++++++++++++++++++++++++---- include/linux/poll.h | 3 +++ 2 files changed, 39 insertions(+), 4 deletions(-) diff --git a/fs/select.c b/fs/select.c index 0fe0e1469df3..d870237e42c7 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 @@ static int max_select_fd(unsigned long n, fd_set_bits *fds) #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); diff --git a/include/linux/poll.h b/include/linux/poll.h index 8c24ef8d9976..fa287f25138d 100644 --- a/include/linux/poll.h +++ b/include/linux/poll.h @@ -32,6 +32,7 @@ typedef void (*poll_queue_proc)(struct file *, wait_queue_head_t *, struct poll_ 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 poll_wait(struct file * filp, wait_queue_head_t * wait_addres 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; };