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From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: "David S. Miller" <davem@redhat.com>, <zaitcev@redhat.com>,
	Oleg Drokin <green@namesys.com>, <linux-kernel@vger.kernel.org>
Subject: [patch] pidhash-2.5.38-A0
Date: Wed, 25 Sep 2002 10:48:49 +0200 (CEST)	[thread overview]
Message-ID: <Pine.LNX.4.44.0209251047040.5857-100000@localhost.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.44.0209251024580.4690-100000@localhost.localdomain>


the attached patch removes the cmpxchg from the PID allocator and replaces
it with a spinlock. This spinlock is hit only a couple of times per
bootup, so it's not a performance issue.

	Ingo

--- linux/kernel/pid.c.orig	Wed Sep 25 10:36:13 2002
+++ linux/kernel/pid.c	Wed Sep 25 10:38:55 2002
@@ -53,6 +53,8 @@
 
 static pidmap_t *map_limit = pidmap_array + PIDMAP_ENTRIES;
 
+static spinlock_t pidmap_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
+
 inline void free_pidmap(int pid)
 {
 	pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
@@ -77,8 +79,13 @@
 			 * Free the page if someone raced with us
 			 * installing it:
 			 */
-			if (cmpxchg(&map->page, NULL, (void *) page))
+			spin_lock(&pidmap_lock);
+			if (map->page)
 				free_page(page);
+			else
+				map->page = (void *)page;
+			spin_unlock(&pidmap_lock);
+
 			if (!map->page)
 				break;
 		}


  reply	other threads:[~2002-09-25  8:34 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-09-25  5:00 cmpxchg in 2.5.38 Pete Zaitcev
2002-09-25  4:54 ` David S. Miller
2002-09-25  7:18 ` Oleg Drokin
2002-09-25  7:47   ` David S. Miller
2002-09-25  8:07     ` Oleg Drokin
2002-09-25  8:26       ` Ingo Molnar
2002-09-25  8:48         ` Ingo Molnar [this message]
2002-09-25 12:04         ` Geert Uytterhoeven
2002-09-25 17:42         ` Pete Zaitcev
2002-09-25 19:34           ` Ingo Molnar
2002-09-25 20:03             ` David S. Miller
2002-09-25 18:59         ` David S. Miller
2002-09-25 19:02         ` David S. Miller

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