Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756510AbZD2H3A (ORCPT ); Wed, 29 Apr 2009 03:29:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752554AbZD2H2r (ORCPT ); Wed, 29 Apr 2009 03:28:47 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:53912 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752130AbZD2H2q (ORCPT ); Wed, 29 Apr 2009 03:28:46 -0400 Date: Wed, 29 Apr 2009 00:20:49 -0700 From: Andrew Morton To: Eric Dumazet Cc: linux kernel , Andi Kleen , David Miller , cl@linux.com, jesse.brandeburg@intel.com, netdev@vger.kernel.org, haoki@redhat.com, mchan@broadcom.com, davidel@xmailserver.org, Ingo Molnar Subject: Re: [PATCH] poll: Avoid extra wakeups in select/poll Message-Id: <20090429002049.4bbc8105.akpm@linux-foundation.org> In-Reply-To: <49F71B63.8010503@cosmosbay.com> References: <49F3308B.1030507@cosmosbay.com> <20090426.020411.157511269.davem@davemloft.net> <49F43B8F.2050907@cosmosbay.com> <87ab60rh8t.fsf@basil.nowhere.org> <49F71B63.8010503@cosmosbay.com> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4391 Lines: 123 On Tue, 28 Apr 2009 17:06:11 +0200 Eric Dumazet wrote: > [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. > Seems that this is a virtuous patch even though Christoph is struggling a bit to test it? > fs/select.c | 28 +++++++++++++++++++++++++--- > include/linux/poll.h | 3 +++ > 2 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/fs/select.c b/fs/select.c > index 0fe0e14..2708187 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); > @@ -418,8 +429,16 @@ 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) > + if (f_op && f_op->poll) { > + if (wait) { > + wait->key = POLLEX_SET; > + if (in & bit) > + wait->key |= POLLIN_SET; > + if (out & bit) > + wait->key |= POLLOUT_SET; > + } > mask = (*f_op->poll)(file, retval ? NULL : wait); > + } Can we (and should we) avoid all that manipulation of wait->key if `retval' is zero? > --- 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 */ I kind of prefer to use plain old -1 for the all-ones pattern. Because it always just works, and doesn't send the reviewer off to check if the type was really u64 or something. It's a bit ugly though. > } > > struct poll_table_entry { > struct file *filp; > + unsigned long key; > wait_queue_t wait; > wait_queue_head_t *wait_address; > }; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/