svn commit: r198868 - in head/sys: amd64/amd64 i386/i386

[Attilio Rao]

2009/11/4 Ed Schouten <ed at 80386.nl>:
> Hi Attilio,
>
> * Attilio Rao <attilio at FreeBSD.org> wrote:
>> Opteron rev E family of processor expose a bug where, in very rare
>> ocassions, memory barriers semantic is not honoured by the hardware
>> itself. As a result, some random breakage can happen in uninvestigable
>> ways (for further explanation see at the content of the commit itself).
>
> Ooh. Sounds like an interesting bug.
>
> The bug doesn't manifest itself on UP, right? If so, maybe we should add
> some very short instructions to the warning on how to disable SMP.

Due to the semantic of the bug, I think that it can manifest itself on
UP and a memory barrier failing on UP means that PREEMPTION can blow
up. Considering this I wouldn't suggest anything different between the
UP vs SMP case.

Attilio


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