Re: [PATCH] i386 spinlocks should use the full 32 bits, not only8 bits

From: Eric Dumazet
Date: Tue Oct 11 2005 - 11:37:58 EST

Linus Torvalds a écrit :

On Tue, 11 Oct 2005, Eric Dumazet wrote:

As NR_CPUS might be > 128, and every spining CPU decrements the lock, we need
to use more than 8 bits for a spinlock. The current (i386/x86_64)
implementations have a (theorical) bug in this area.

I don't think there are any x86 machines with > 128 CPU's right now.

The advantage of the byte lock is that a "movb $0" is three bytes shorter than a "movl $0". And that's the unlock sequence.

1) Would you prefer to change arch/i386/Kconfig

config NR_CPUS
int "Maximum number of CPUs (2-255)"
range 2 255

2) The unlock sequence is not anymore inlined. It appears twice or three times in the kernel.

3) i386 code is often taken as the base when a port is done. For example x86_64 has the same problem.

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