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Re: AIM7 40% regression with 2.6.26-rc1

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To: Ingo Molnar <mingo@...>
Cc: Andi Kleen <andi@...>, Matthew Wilcox <matthew@...>, Zhang, Yanmin <yanmin_zhang@...>, LKML <linux-kernel@...>, Alexander Viro <viro@...>, Andrew Morton <akpm@...>
Date: Wednesday, May 7, 2008 - 1:55 pm

On Wed, 7 May 2008, Ingo Molnar wrote:

Hmm. I do agree that _cond_resched() looks a bit iffy, although in a safe 
way. It uses just

	!(preempt_count() & PREEMPT_ACTIVE)

to see whether it can schedule, and it should probably use in_atomic() 
which ignores the kernel lock.

But right now, that whole thing is disabled if PREEMPT is on anyway, so in 
effect (with my test patch, at least) cond_preempt() would just be a no-op 
if PREEMPT is on, even if BKL isn't preemptable.

So it doesn't look buggy, but it looks like it might cause longer 
latencies than strictly necessary. And if somebody depends on 
cond_resched() to avoid some bad livelock situation, that would obviously 
not work (but that sounds like a fundamental bug anyway, I really hope 
nobody has ever written their code that way).


Yes, some silly bug sounds more likely. Especially considering how many 
different cases there were (semaphores vs spinlocks vs preemptable 
spinlocks).

			Linus
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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)
[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)
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