From: Ingo Molnar <mingo@elte.hu>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <matthew@wil.cx>,
"J. Bruce Fields" <bfields@citi.umich.edu>,
"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@ftp.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: AIM7 40% regression with 2.6.26-rc1
Date: Tue, 6 May 2008 19:39:01 +0200 [thread overview]
Message-ID: <20080506173900.GA9014@elte.hu> (raw)
In-Reply-To: <20080506102153.5484c6ac.akpm@linux-foundation.org>
* Andrew Morton <akpm@linux-foundation.org> wrote:
> Finally: how come we regressed by swapping the semaphore
> implementation anyway? We went from one sleeping lock implementation
> to another - I'd have expected performance to be pretty much the same.
>
> <looks at the implementation>
>
> down(), down_interruptible() and down_try() should use
> spin_lock_irq(), not irqsave.
>
> up() seems to be doing wake-one, FIFO which is nice. Did the
> implementation which we just removed also do that? Was it perhaps
> accidentally doing LIFO or something like that?
i just checked the old implementation on x86. It used
lib/semaphore-sleepers.c which does one weird thing:
- __down() when it returns wakes up yet another task via
wake_up_locked().
i.e. we'll always keep yet another task in flight. This can mask wakeup
latencies especially when it takes time.
The patch (hack) below tries to emulate this weirdness - it 'kicks'
another task as well and keeps it busy. Most of the time this just
causes extra scheduling, but if AIM7 is _just_ saturating the number of
CPUs, it might make a difference. Yanmin, does the patch below make any
difference to the AIM7 results?
( it would be useful data to get a meaningful context switch trace from
the whole regressed workload, and compare it to a context switch trace
with the revert added. )
Ingo
---
kernel/semaphore.c | 10 ++++++++++
1 file changed, 10 insertions(+)
Index: linux/kernel/semaphore.c
===================================================================
--- linux.orig/kernel/semaphore.c
+++ linux/kernel/semaphore.c
@@ -261,4 +261,14 @@ static noinline void __sched __up(struct
list_del(&waiter->list);
waiter->up = 1;
wake_up_process(waiter->task);
+
+ if (likely(list_empty(&sem->wait_list)))
+ return;
+ /*
+ * Opportunistically wake up another task as well but do not
+ * remove it from the list:
+ */
+ waiter = list_first_entry(&sem->wait_list,
+ struct semaphore_waiter, list);
+ wake_up_process(waiter->task);
}
next prev parent reply other threads:[~2008-05-06 17:43 UTC|newest]
Thread overview: 140+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-05-06 5:48 AIM7 40% regression with 2.6.26-rc1 Zhang, Yanmin
2008-05-06 11:18 ` Matthew Wilcox
2008-05-06 11:44 ` Ingo Molnar
2008-05-06 12:09 ` Matthew Wilcox
2008-05-06 16:23 ` Matthew Wilcox
2008-05-06 16:36 ` Linus Torvalds
2008-05-06 16:42 ` Matthew Wilcox
2008-05-06 16:39 ` Alan Cox
2008-05-06 16:51 ` Matthew Wilcox
2008-05-06 16:45 ` Alan Cox
2008-05-06 17:42 ` Linus Torvalds
2008-05-06 20:28 ` Linus Torvalds
2008-05-06 16:44 ` J. Bruce Fields
2008-05-06 17:21 ` Andrew Morton
2008-05-06 17:31 ` Matthew Wilcox
2008-05-06 17:49 ` Ingo Molnar
2008-05-06 18:07 ` Andrew Morton
2008-05-11 11:11 ` Matthew Wilcox
2008-05-06 17:39 ` Ingo Molnar [this message]
2008-05-07 6:49 ` Zhang, Yanmin
2008-05-06 17:45 ` Linus Torvalds
2008-05-07 16:38 ` Matthew Wilcox
2008-05-07 16:55 ` Linus Torvalds
2008-05-07 17:08 ` Linus Torvalds
2008-05-07 17:16 ` Andrew Morton
2008-05-07 17:27 ` Linus Torvalds
2008-05-07 17:22 ` Ingo Molnar
2008-05-07 17:25 ` Ingo Molnar
2008-05-07 17:31 ` Linus Torvalds
2008-05-07 17:47 ` Linus Torvalds
2008-05-07 17:49 ` Ingo Molnar
2008-05-07 18:02 ` Linus Torvalds
2008-05-07 18:17 ` Ingo Molnar
2008-05-07 18:27 ` Linus Torvalds
2008-05-07 18:43 ` Ingo Molnar
2008-05-07 19:01 ` Linus Torvalds
2008-05-07 19:09 ` Ingo Molnar
2008-05-07 19:24 ` Matthew Wilcox
2008-05-07 19:44 ` Linus Torvalds
2008-05-07 20:00 ` Oi. NFS people. Read this Matthew Wilcox
2008-05-07 22:10 ` Trond Myklebust
2008-05-09 1:43 ` J. Bruce Fields
2008-05-08 3:24 ` AIM7 40% regression with 2.6.26-rc1 Zhang, Yanmin
2008-05-08 3:34 ` Linus Torvalds
2008-05-08 4:37 ` Zhang, Yanmin
2008-05-08 14:58 ` Linus Torvalds
2008-05-07 2:11 ` Zhang, Yanmin
2008-05-07 3:41 ` Zhang, Yanmin
2008-05-07 3:59 ` Andrew Morton
2008-05-07 4:46 ` Zhang, Yanmin
2008-05-07 6:26 ` Ingo Molnar
2008-05-07 6:28 ` Ingo Molnar
2008-05-07 7:05 ` Zhang, Yanmin
2008-05-07 11:00 ` Andi Kleen
2008-05-07 11:46 ` Matthew Wilcox
2008-05-07 12:21 ` Andi Kleen
2008-05-07 14:36 ` Linus Torvalds
2008-05-07 14:35 ` Alan Cox
2008-05-07 15:00 ` Linus Torvalds
2008-05-07 15:02 ` Linus Torvalds
2008-05-07 14:57 ` Andi Kleen
2008-05-07 15:31 ` Andrew Morton
2008-05-07 16:22 ` Matthew Wilcox
2008-05-07 15:19 ` Linus Torvalds
2008-05-07 17:14 ` Ingo Molnar
2008-05-08 2:44 ` Zhang, Yanmin
2008-05-08 3:29 ` Linus Torvalds
2008-05-08 4:08 ` Zhang, Yanmin
2008-05-08 4:17 ` Linus Torvalds
2008-05-08 12:01 ` [patch] speed up / fix the new generic semaphore code (fix AIM7 40% regression with 2.6.26-rc1) Ingo Molnar
2008-05-08 12:28 ` Ingo Molnar
2008-05-08 14:43 ` Ingo Molnar
2008-05-08 15:10 ` [git pull] scheduler fixes Ingo Molnar
2008-05-08 15:33 ` Adrian Bunk
2008-05-08 15:41 ` Ingo Molnar
2008-05-08 19:42 ` Adrian Bunk
2008-05-11 11:03 ` Matthew Wilcox
2008-05-11 11:14 ` Matthew Wilcox
2008-05-11 11:48 ` Matthew Wilcox
2008-05-11 12:50 ` Ingo Molnar
2008-05-11 12:52 ` Ingo Molnar
2008-05-11 13:02 ` Matthew Wilcox
2008-05-11 13:26 ` Matthew Wilcox
2008-05-11 14:00 ` Ingo Molnar
2008-05-11 14:18 ` Matthew Wilcox
2008-05-11 14:42 ` Ingo Molnar
2008-05-11 14:48 ` Matthew Wilcox
2008-05-11 15:19 ` Ingo Molnar
2008-05-11 15:29 ` Matthew Wilcox
2008-05-13 14:11 ` Ingo Molnar
2008-05-13 14:21 ` Matthew Wilcox
2008-05-13 14:42 ` Ingo Molnar
2008-05-13 15:28 ` Matthew Wilcox
2008-05-13 17:13 ` Ingo Molnar
2008-05-13 17:22 ` Linus Torvalds
2008-05-13 21:05 ` Ingo Molnar
2008-05-11 13:54 ` Ingo Molnar
2008-05-11 14:22 ` Matthew Wilcox
2008-05-11 14:32 ` Ingo Molnar
2008-05-11 14:46 ` Matthew Wilcox
2008-05-11 16:47 ` Linus Torvalds
2008-05-11 13:01 ` Ingo Molnar
2008-05-11 13:06 ` Matthew Wilcox
2008-05-11 13:45 ` Ingo Molnar
2008-05-11 14:10 ` Sven Wegener
2008-05-08 16:02 ` [patch] speed up / fix the new generic semaphore code (fix AIM7 40% regression with 2.6.26-rc1) Linus Torvalds
2008-05-08 18:30 ` Linus Torvalds
2008-05-08 20:19 ` Ingo Molnar
2008-05-08 20:27 ` Linus Torvalds
2008-05-08 21:45 ` Ingo Molnar
2008-05-08 22:02 ` Ingo Molnar
2008-05-08 22:55 ` Linus Torvalds
2008-05-08 23:07 ` Linus Torvalds
2008-05-08 23:14 ` Linus Torvalds
2008-05-08 23:16 ` Alan Cox
2008-05-08 23:33 ` Linus Torvalds
2008-05-08 23:27 ` Alan Cox
2008-05-09 6:50 ` Ingo Molnar
2008-05-09 8:29 ` Andi Kleen
2008-05-08 13:20 ` Matthew Wilcox
2008-05-08 15:01 ` Ingo Molnar
2008-05-08 13:56 ` Arjan van de Ven
2008-05-08 6:43 ` AIM7 40% regression with 2.6.26-rc1 Ingo Molnar
2008-05-08 6:48 ` Andrew Morton
2008-05-08 7:14 ` Zhang, Yanmin
2008-05-08 7:39 ` Ingo Molnar
2008-05-08 8:44 ` Zhang, Yanmin
2008-05-08 9:21 ` Ingo Molnar
2008-05-08 9:29 ` Ingo Molnar
2008-05-08 9:30 ` Zhang, Yanmin
2008-05-07 16:20 ` Ingo Molnar
2008-05-07 16:35 ` Linus Torvalds
2008-05-07 17:05 ` Ingo Molnar
2008-05-07 17:24 ` Linus Torvalds
2008-05-07 17:36 ` Ingo Molnar
2008-05-07 17:55 ` Linus Torvalds
2008-05-07 17:59 ` Matthew Wilcox
2008-05-07 18:17 ` Linus Torvalds
2008-05-07 18:49 ` Ingo Molnar
2008-05-07 13:59 ` Alan Cox
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