From: Eric Dumazet <dada1@cosmosbay.com>
To: Linus Torvalds <torvalds@osdl.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] i386 spinlocks should use the full 32 bits, not only 8 bits
Date: Tue, 11 Oct 2005 18:36:29 +0200 [thread overview]
Message-ID: <434BEA0D.9010802@cosmosbay.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0510110902130.14597@g5.osdl.org>
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.
Eric
next prev parent reply other threads:[~2005-10-11 16:36 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-11 4:04 i386 spinlock fairness: bizarre test results Chuck Ebbert
2005-10-11 9:42 ` Eric Dumazet
2005-10-11 13:00 ` Alan Cox
2005-10-11 14:44 ` Linus Torvalds
2005-10-11 15:32 ` [PATCH] i386 spinlocks should use the full 32 bits, not only 8 bits Eric Dumazet
2005-10-11 16:03 ` Linus Torvalds
2005-10-11 16:36 ` Eric Dumazet [this message]
2005-10-11 16:54 ` Linus Torvalds
2005-10-11 16:55 ` Linus Torvalds
2005-10-17 7:03 ` Andrew Morton
2005-10-17 7:20 ` Arjan van de Ven
2005-10-20 21:50 ` Ingo Molnar
2005-10-20 21:57 ` Linus Torvalds
2005-10-20 22:02 ` Ingo Molnar
2005-10-20 22:15 ` Linus Torvalds
2005-10-20 22:27 ` Ingo Molnar
2005-10-20 22:44 ` Andrew Morton
2005-10-20 22:53 ` Ingo Molnar
2005-10-20 23:01 ` Andrew Morton
2005-10-20 23:26 ` Ingo Molnar
2005-10-27 16:54 ` Paul Jackson
2005-10-11 17:59 ` Andi Kleen
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