From: Ralf Baechle <ralf@linux-mips.org>
To: Johannes Dickgreber <tanzy@gmx.de>
Cc: Linux MIPS List <linux-mips@linux-mips.org>
Subject: Re: Questions for CONFIG_WEAK_ORDERING and CONFIG_WEAK_REORDERING_BEYOND_LLSC
Date: Mon, 13 Oct 2008 22:50:54 +0100 [thread overview]
Message-ID: <20081013215054.GB8145@linux-mips.org> (raw)
In-Reply-To: <48F39B18.9030601@gmx.de>
On Mon, Oct 13, 2008 at 09:01:44PM +0200, Johannes Dickgreber wrote:
> If a cpu is WEAK_ORDERING schouldn't it do a sync independent of CONFIG_SMP ?
>
> And if it is a SMP system schouldn't it do a sync independent of CONFIG_WEAK_ORDERING ?
>
> And if a cpu has no sync with LLSC schouldn't it do a sync independent of CONFIG_SMP ?
>
> All together, is the following the right thing to do ?
A processor is always consistently ordered wrt. to itself, so uniprocessor
cores never need SYNCs even if that processor was weakly ordered in a
multiprocessor systems.
A while ago I walked through all mb(), rmb() and wmb() uses in the generic
code. None of the ones I verified is actually needed on uniprocessor
kernels. Ocasionally one of these functions is used to maintain I/O
ordering but again other mechanisms are prefered for that purpose.
Ralf
prev parent reply other threads:[~2008-10-13 21:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-13 19:01 Questions for CONFIG_WEAK_ORDERING and CONFIG_WEAK_REORDERING_BEYOND_LLSC Johannes Dickgreber
2008-10-13 21:50 ` Ralf Baechle [this message]
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