Re: [patch] speed up / fix the new generic semaphore code (fix AIM7 40% regression with 2.6.26-rc1)

!MAILaRCHIVE_VOTE_RePLACE
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
To: Linus Torvalds <torvalds@...>
Cc: Zhang, Yanmin <yanmin_zhang@...>, Andi Kleen <andi@...>, Matthew Wilcox <matthew@...>, LKML <linux-kernel@...>, Alexander Viro <viro@...>, Andrew Morton <akpm@...>, Thomas Gleixner <tglx@...>, H. Peter Anvin <hpa@...>
Date: Thursday, May 8, 2008 - 10:43 am

* Ingo Molnar <mingo@elte.hu> wrote:


a second update patch, i've further simplified the semaphore wakeup 
logic: there's no need for the wakeup to remove the task from the wait 
list. This will make them a slighly bit more fair, but more importantly, 
this closes a race in my first patch for the unlikely case of a signal 
(or a timeout) and an unlock coming in at the same time and the task not 
getting removed from the wait-list.

( my performance testing with 2000 AIM7 tasks on a quad never hit that
  race but x86.git QA actually triggered it after about 30 random kernel
  bootups and it caused a nasty crash and lockup. )

	Ingo

---------------->
Subject: sem: simplify queue management
From: Ingo Molnar <mingo@elte.hu>
Date: Tue May 06 19:32:42 CEST 2008

kernel/semaphore.o:

   text	   data	    bss	    dec	    hex	filename
   1040	      0	      0	   1040	    410	semaphore.o.before
    975	      0	      0	    975	    3cf	semaphore.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/semaphore.c |   32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

Index: linux/kernel/semaphore.c
===================================================================
--- linux.orig/kernel/semaphore.c
+++ linux/kernel/semaphore.c
@@ -202,33 +202,34 @@ static inline int __sched __down_common(
 {
 	struct task_struct *task = current;
 	struct semaphore_waiter waiter;
+	int ret = 0;
 
 	waiter.task = task;
+	list_add_tail(&waiter.list, &sem->wait_list);
 
 	for (;;) {
-		list_add_tail(&waiter.list, &sem->wait_list);
-
-		if (state == TASK_INTERRUPTIBLE && signal_pending(task))
-			goto interrupted;
-		if (state == TASK_KILLABLE && fatal_signal_pending(task))
-			goto interrupted;
-		if (timeout <= 0)
-			goto timed_out;
+		if (state == TASK_INTERRUPTIBLE && signal_pending(task)) {
+			ret = -EINTR;
+			break;
+		}
+		if (state == TASK_KILLABLE && fatal_signal_pending(task)) {
+			ret = -EINTR;
+			break;
+		}
+		if (timeout <= 0) {
+			ret = -ETIME;
+			break;
+		}
 		__set_task_state(task, state);
 		spin_unlock_irq(&sem->lock);
 		timeout = schedule_timeout(timeout);
 		spin_lock_irq(&sem->lock);
 		if (sem->count > 0)
-			return 0;
+			break;
 	}
 
- timed_out:
-	list_del(&waiter.list);
-	return -ETIME;
-
- interrupted:
 	list_del(&waiter.list);
-	return -EINTR;
+	return ret;
 }
 
 static noinline void __sched __down(struct semaphore *sem)
@@ -255,6 +256,5 @@ static noinline void __sched __up(struct
 {
 	struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
 						struct semaphore_waiter, list);
-	list_del(&waiter->list);
 	wake_up_process(waiter->task);
 }
--
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]

Messages in current thread:
AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Tue May 6, 1:48 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Tue May 6, 7:44 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Tue May 6, 10:11 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Tue May 6, 11:41 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Andi Kleen, (Wed May 7, 7:00 am)
Re: AIM7 40% regression with 2.6.26-rc1, Alan Cox, (Wed May 7, 9:59 am)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Wed May 7, 7:46 am)
Re: AIM7 40% regression with 2.6.26-rc1, Andi Kleen, (Wed May 7, 8:21 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 10:36 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 12:20 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 12:35 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:05 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:24 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:36 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:55 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Wed May 7, 1:59 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 2:17 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 2:49 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 11:19 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Wed May 7, 10:44 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Thu May 8, 2:43 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Thu May 8, 3:14 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Thu May 8, 3:39 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Thu May 8, 4:44 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Thu May 8, 5:21 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Thu May 8, 5:30 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Thu May 8, 5:29 am)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Thu May 8, 2:48 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 11:29 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Thu May 8, 12:08 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Thu May 8, 12:17 am)
Re: [patch] speed up / fix the new generic semaphore code (f..., Ingo Molnar, (Thu May 8, 10:43 am)
[git pull] scheduler fixes, Ingo Molnar, (Thu May 8, 11:10 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 7:03 am)
Re: [git pull] scheduler fixes, Sven Wegener, (Sun May 11, 10:10 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 9:01 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 9:06 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 9:45 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 7:48 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 8:50 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 8:52 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 9:02 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 9:54 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 10:22 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 10:32 am)
Re: [git pull] scheduler fixes, Linus Torvalds, (Sun May 11, 12:47 pm)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 10:46 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 9:26 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 10:00 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 10:18 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 10:42 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 10:48 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Sun May 11, 11:19 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 11:29 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Tue May 13, 10:11 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Tue May 13, 10:21 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Tue May 13, 10:42 am)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Tue May 13, 11:28 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Tue May 13, 1:13 pm)
Re: [git pull] scheduler fixes, Linus Torvalds, (Tue May 13, 1:22 pm)
Re: [git pull] scheduler fixes, Ingo Molnar, (Tue May 13, 5:05 pm)
Re: [git pull] scheduler fixes, Matthew Wilcox, (Sun May 11, 7:14 am)
Re: [git pull] scheduler fixes, Adrian Bunk, (Thu May 8, 11:33 am)
Re: [git pull] scheduler fixes, Ingo Molnar, (Thu May 8, 11:41 am)
Re: [git pull] scheduler fixes, Adrian Bunk, (Thu May 8, 3:42 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:14 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Andi Kleen, (Wed May 7, 10:57 am)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Wed May 7, 11:31 am)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Wed May 7, 12:22 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Alan Cox, (Wed May 7, 10:35 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 11:00 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 11:02 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 2:26 am)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 2:28 am)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Wed May 7, 3:05 am)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Tue May 6, 11:59 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Wed May 7, 12:46 am)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 8:09 am)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 12:23 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Wed May 7, 11:24 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 11:34 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Thu May 8, 12:37 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Thu May 8, 10:58 am)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Tue May 6, 1:21 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Wed May 7, 12:38 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 12:55 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:08 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:22 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:31 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:49 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 2:02 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 2:17 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 2:27 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 2:43 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 3:01 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Wed May 7, 3:24 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 3:44 pm)
Oi. NFS people. Read this., Matthew Wilcox, (Wed May 7, 4:00 pm)
Re: Oi. NFS people. Read this., Trond Myklebust, (Wed May 7, 6:10 pm)
Re: Oi. NFS people. Read this., J. Bruce Fields, (Thu May 8, 9:43 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 3:09 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:47 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Wed May 7, 1:25 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Wed May 7, 1:16 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Wed May 7, 1:27 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Tue May 6, 1:45 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Tue May 6, 1:39 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Zhang, Yanmin, (Wed May 7, 2:49 am)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 1:31 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Ingo Molnar, (Tue May 6, 1:49 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Andrew Morton, (Tue May 6, 2:07 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Sun May 11, 7:11 am)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Tue May 6, 12:36 pm)
Re: AIM7 40% regression with 2.6.26-rc1, J. Bruce Fields, (Tue May 6, 12:44 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 12:42 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Tue May 6, 4:28 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Alan Cox, (Tue May 6, 12:39 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 12:51 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Linus Torvalds, (Tue May 6, 1:42 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Alan Cox, (Tue May 6, 12:45 pm)
Re: AIM7 40% regression with 2.6.26-rc1, Matthew Wilcox, (Tue May 6, 7:18 am)