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Re: SMP, barriers, etc.
From: |
Samuel Thibault |
Subject: |
Re: SMP, barriers, etc. |
Date: |
Sat, 26 Dec 2009 11:55:45 +0100 |
User-agent: |
Mutt/1.5.12-2006-07-14 |
Da Zheng, le Sat 26 Dec 2009 16:21:55 +0800, a écrit :
> Hi,
>
> Samuel Thibault wrote:
> > (I've cleaned To: and subject a bit :)
> >
> > Da Zheng, le Wed 23 Dec 2009 21:23:23 +0800, a écrit :
> >> Samuel Thibault wrote:
> >>>> Is there anything else we should worry about?
> >>> Ordering. See /usr/src/linux/Documentation/memory-barriers.txt
> >> It's a long file. There are a lot to study:)
> >
> > Yes, it's very instructive.
> After I read this introduction, I checked some atomic operations
> implementation such as atomic_add_return in Linux for Aphla processors.
> Before and after these operations change the variable, they put memory
> barriers. So it's something like this:
> smp_mb();
> operations;
> smp_mb();
>
> But the problem is: on SMP, a variable's value can always been changed by
> another processor after the first memory barrier is called. Thus, the CPU
> does an operation on the stale value. There seems to be no way that we can
> guarantee that the variable has the latest value at the moment the CPU is
> doing the operation on it.
Yes, that's why the operations have a loop that keeps retrying until the
result is as expected.
Samuel
- Re: What would it take...., (continued)
- Re: What would it take...., Samuel Thibault, 2009/12/23
- Re: What would it take...., Da Zheng, 2009/12/23
- Re: What would it take...., Samuel Thibault, 2009/12/23
- Re: What would it take...., Samuel Thibault, 2009/12/23
- Re: What would it take...., Da Zheng, 2009/12/23
- Re: What would it take...., Da Zheng, 2009/12/23
- Re: What would it take...., Samuel Thibault, 2009/12/23
- Re: What would it take...., Da Zheng, 2009/12/23
- SMP, barriers, etc., Samuel Thibault, 2009/12/23
- Re: SMP, barriers, etc., Da Zheng, 2009/12/26
- Re: SMP, barriers, etc.,
Samuel Thibault <=
- Re: SMP, barriers, etc., Da Zheng, 2009/12/27
- Re: SMP, barriers, etc., Samuel Thibault, 2009/12/27
- Re: SMP, barriers, etc., Da Zheng, 2009/12/27
- Re: SMP, barriers, etc., Samuel Thibault, 2009/12/27
- Re: SMP, barriers, etc., Da Zheng, 2009/12/28
- Re: SMP, barriers, etc., Samuel Thibault, 2009/12/28
- Re: SMP, barriers, etc., Da Zheng, 2009/12/28
- Re: SMP, barriers, etc., Samuel Thibault, 2009/12/28
Re: What would it take...., olafBuddenhagen, 2009/12/23