Re: namei() query

From: Linus Torvalds (
Date: Fri Apr 21 2000 - 20:21:53 EST

On Sat, 22 Apr 2000 wrote:
> Spin-unlock is much worse case.
> As stated in i386/spinlock.h "movb $0,%0" is far better than
> "lock ; btrl $0,%0", mostly because of instruction serialization
> caused by the locked operation.


I have conflicting reports about the safety of "movb" from Intel.
According to some people in there, "movb" is always safe, and there should
not be any need for any config option at all.

However, at the same time my original contact at intel was Andy Glew, who
probably knows more about the ia32 core than anybody else I know. And Andy
says that yes "movb" is legal, but that some very early P6 steppings may
be buggy. And Andy is God.

I'd hate to have a kernel that works 99% of the time but then has
occasional problems on some very rare machines that are really hard to
track down. But I'd _almost_ like to just make the movb the default and
have a CONFIG_BROKEN_P6_ORDERING options for the very very special case.


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