[PATCH] eventpoll : Suppress a short lived lock from struct file

[Eric Dumazet <dada1@cosmosbay.com>]

Hi Davide

I found in my tests that there is no need to have a f_ep_lock spinlock
attached to each struct file, using 8 bytes on 64bits platforms. The
lock is hold for a very short time period and can be global, with almost
no change in performance for applications using epoll, and a gain for
all others.

Thank you
Eric Dumazet

[PATCH] eventpoll : Suppress a short lived lock from struct file

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

--- linux-2.6.12/fs/eventpoll.c	2005-06-17 21:48:29.000000000 +0200
+++ linux-2.6.12-ed/fs/eventpoll.c	2005-07-11 08:56:07.000000000 +0200
@@ -179,6 +179,8 @@
 	spinlock_t lock;
 };
 
+static DEFINE_SPINLOCK(f_ep_lock);
+
 /*
  * This structure is stored inside the "private_data" member of the file
  * structure and rapresent the main data sructure for the eventpoll
@@ -426,7 +428,6 @@
 {
 
 	INIT_LIST_HEAD(&file->f_ep_links);
-	spin_lock_init(&file->f_ep_lock);
 }
 
 
@@ -967,9 +968,9 @@
 		goto eexit_2;
 
 	/* Add the current item to the list of active epoll hook for this file */
-	spin_lock(&tfile->f_ep_lock);
+	spin_lock(&f_ep_lock);
 	list_add_tail(&epi->fllink, &tfile->f_ep_links);
-	spin_unlock(&tfile->f_ep_lock);
+	spin_unlock(&f_ep_lock);
 
 	/* We have to drop the new item inside our item list to keep track of it */
 	write_lock_irqsave(&ep->lock, flags);
@@ -1160,7 +1161,6 @@
 {
 	int error;
 	unsigned long flags;
-	struct file *file = epi->ffd.file;
 
 	/*
 	 * Removes poll wait queue hooks. We _have_ to do this without holding
@@ -1173,10 +1173,10 @@
 	ep_unregister_pollwait(ep, epi);
 
 	/* Remove the current item from the list of epoll hooks */
-	spin_lock(&file->f_ep_lock);
+	spin_lock(&f_ep_lock);
 	if (EP_IS_LINKED(&epi->fllink))
 		EP_LIST_DEL(&epi->fllink);
-	spin_unlock(&file->f_ep_lock);
+	spin_unlock(&f_ep_lock);
 
 	/* We need to acquire the write IRQ lock before calling ep_unlink() */
 	write_lock_irqsave(&ep->lock, flags);
--- linux-2.6.12/include/linux/fs.h	2005-06-17 21:48:29.000000000 +0200
+++ linux-2.6.12-ed/include/linux/fs.h	2005-07-11 08:58:02.000000000 +0200
@@ -597,7 +597,6 @@
 #ifdef CONFIG_EPOLL
 	/* Used by fs/eventpoll.c to link all the hooks to this file */
 	struct list_head	f_ep_links;
-	spinlock_t		f_ep_lock;
 #endif /* #ifdef CONFIG_EPOLL */
 	struct address_space	*f_mapping;
 };