[patch] epoll bits 0.30 ...

[patch] epoll bits 0.30 ...

[Davide Libenzi]

These are the latest few bits for epoll. Changes :

*) Some constant adjusted

*) Comments plus

*) Better hash initialization

*) Correct timeout setup




- Davide




eventpoll.c |   55 ++++++++++++++++++++++++++++++++++++++-----------------
1 files changed, 38 insertions, 17 deletions





diff -Nru linux-2.5.46.vanilla/fs/eventpoll.c linux-2.5.46.epoll/fs/eventpoll.c
--- linux-2.5.46.vanilla/fs/eventpoll.c	Mon Nov  4 15:45:35 2002
+++ linux-2.5.46.epoll/fs/eventpoll.c	Mon Nov  4 15:50:27 2002
@@ -61,8 +61,12 @@
 /* Maximum storage for the eventpoll interest set */
 #define EP_MAX_FDS_SIZE (1024 * 128)

-/* We don't want the hash to be smaller than this */
-#define EP_MIN_HASH_SIZE 101
+/*
+ * We don't want the hash to be smaller than this. This is basically
+ * the highest prime lower than (PAGE_SIZE / sizeof(struct list_head)).
+ */
+#define EP_MIN_HASH_SIZE 509
+
 /*
  * Event buffer dimension used to cache events before sending them in
  * userspace with a __copy_to_user(). The event buffer is in stack,
@@ -188,6 +192,7 @@


 static int ep_is_prime(int n);
+static int ep_size_hash(int hintsize);
 static int ep_getfd(int *efd, struct inode **einode, struct file **efile);
 static int ep_alloc_pages(char **pages, int numpages);
 static int ep_free_pages(char **pages, int numpages);
@@ -252,14 +257,14 @@



-/* Report if the number is prime. Needed to correctly size the hash  */
+/* Report if the number is prime. Needed to correctly size the hash */
 static int ep_is_prime(int n)
 {

 	if (n > 3) {
 		if (n & 1) {
 			int i, hn = n / 2;
-
+
 			for (i = 3; i < hn; i += 2)
 				if (!(n % i))
 					return 0;
@@ -296,9 +301,30 @@
 }


+static int ep_size_hash(int hintsize)
+{
+	int maxsize = (EP_MAX_HPAGES - 1) * EP_HENTRY_X_PAGE;
+
+	/*
+	 * Search the nearest prime number higher than "hintsize" and
+	 * smaller than "maxsize".
+	 */
+	for (; !ep_is_prime(hintsize); hintsize++);
+	if (hintsize < EP_MIN_HASH_SIZE)
+		hintsize = EP_MIN_HASH_SIZE;
+	else if (hintsize >= maxsize)
+		for (hintsize = maxsize - 1; !ep_is_prime(hintsize); hintsize--);
+
+	return hintsize;
+}
+
+
 /*
  * It opens an eventpoll file descriptor by suggesting a storage of "size"
- * file descriptors. It is the kernel part of the userspace epoll_create(2).
+ * file descriptors. The size parameter is just an hint about how to size
+ * data structures. It won't prevent the user to store more than "size"
+ * file descriptors inside the epoll interface. It is the kernel part of
+ * the userspace epoll_create(2).
  */
 asmlinkage int sys_epoll_create(int size)
 {
@@ -309,10 +335,8 @@
 	DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
 		     current, size));

-	/* Search the nearest prime number higher than "size" */
-	for (; !ep_is_prime(size); size++);
-	if (size < EP_MIN_HASH_SIZE)
-		size = EP_MIN_HASH_SIZE;
+	/* Correctly size the hash */
+	size = ep_size_hash(size);

 	/*
 	 * Creates all the items needed to setup an eventpoll file. That is,
@@ -567,7 +591,7 @@
 eexit_2:
 	put_filp(file);
 eexit_1:
-	return error;
+	return error;
 }


@@ -723,8 +747,7 @@
 	write_unlock_irqrestore(&eplock, flags);

 	/* Free hash pages */
-	if (ep->nhpages > 0)
-		ep_free_pages(ep->hpages, ep->nhpages);
+	ep_free_pages(ep->hpages, ep->nhpages);
 }


@@ -1126,12 +1149,10 @@
 	wait_queue_t wait;

 	/*
-	 * Calculate the timeout by checking for the "infinite" value ( -1 )
-	 * and the overflow condition ( > MAX_SCHEDULE_TIMEOUT / HZ ). The
-	 * passed timeout is in milliseconds, that why (t * HZ) / 1000.
+	 * Calculate the timeout by checking for the "infinite" value ( -1 ).
+	 * The passed timeout is in milliseconds, that why (t * HZ) / 1000.
 	 */
-	jtimeout = timeout == -1 || timeout > MAX_SCHEDULE_TIMEOUT / HZ ?
-		MAX_SCHEDULE_TIMEOUT: (timeout * HZ) / 1000;
+	jtimeout = timeout == -1 ? MAX_SCHEDULE_TIMEOUT: (timeout * HZ) / 1000;

 retry:
 	write_lock_irqsave(&ep->lock, flags);

Re: [patch] epoll bits 0.30 ...

[Rusty Russell]

On Mon, 4 Nov 2002 19:44:29 -0800 (PST)
Davide Libenzi <davidel@xmailserver.org> wrote:

> 
> These are the latest few bits for epoll. Changes :
> 
> *) Some constant adjusted
> 
> *) Comments plus
> 
> *) Better hash initialization

Um, why doesn't this use linux/hash.h?  Haven't looked hard, but...

Cheers,
Rusty.
-- 
   there are those who do and those who hang on and you don't see too
   many doers quoting their contemporaries.  -- Larry McVoy

Re: [patch] epoll bits 0.30 ...

[Davide Libenzi]

On Wed, 6 Nov 2002, Rusty Russell wrote:

> On Mon, 4 Nov 2002 19:44:29 -0800 (PST)
> Davide Libenzi <davidel@xmailserver.org> wrote:
>
> >
> > These are the latest few bits for epoll. Changes :
> >
> > *) Some constant adjusted
> >
> > *) Comments plus
> >
> > *) Better hash initialization
>
> Um, why doesn't this use linux/hash.h?  Haven't looked hard, but...

Rusty, the hash is not under pressure over there. The only time seeks is
performed is at file removal ( from the set ) and eventually at file
modify. There's a direct link between the wait queue and its item during
the high frequency event delivery, so need seek is performed.




- Davide

Re: [patch] epoll bits 0.30 ...

[Davide Libenzi]

On Wed, 6 Nov 2002, Davide Libenzi wrote:

> Rusty, the hash is not under pressure over there. The only time seeks is
> performed is at file removal ( from the set ) and eventually at file
> modify. There's a direct link between the wait queue and its item during
> the high frequency event delivery, so need seek is performed.

s/so need seek is performed/so no seek is performed/



- Davide

Re: [patch] epoll bits 0.30 ...

[Jamie Lokier]

Davide Libenzi wrote:
> Rusty, the hash is not under pressure over there. The only time seeks is
> performed is at file removal ( from the set ) and eventually at file
> modify. There's a direct link between the wait queue and its item during
> the high frequency event delivery, so need seek is performed.

It does seem peculiar to use a prime-sized hash table, though.  These
days, good power-of-two-sized hash functions are well known.

-- Jamie

Re: [patch] epoll bits 0.30 ...

[Davide Libenzi]

On Fri, 8 Nov 2002, Jamie Lokier wrote:

> Davide Libenzi wrote:
> > Rusty, the hash is not under pressure over there. The only time seeks is
> > performed is at file removal ( from the set ) and eventually at file
> > modify. There's a direct link between the wait queue and its item during
> > the high frequency event delivery, so need seek is performed.
>
> It does seem peculiar to use a prime-sized hash table, though.  These
> days, good power-of-two-sized hash functions are well known.

To make everyone happy the latest code uses hash.h :)



- Davide