linux-kernel - Re: queued spinlock code and results

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Message-ID: <Pine.LNX.4.64.0707091210510.15898@alien.or.mcafeemobile.com>
Date:	Mon, 9 Jul 2007 12:16:26 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: queued spinlock code and results

On Mon, 9 Jul 2007, Davide Libenzi wrote:

> #define ZLOCK_INIT(l) (l)[0] = 0, (l)[1] = 0
> static inline void zlock(short *lock)
> {
> 	__asm__ __volatile__ ("lock ; xaddl %%eax, %0\n\t"
> 			      "mov %%eax, %%ebx\n\t"
> 			      "shr $16, %%ebx\n\t"
> 			      "1:\n\t"
> 			      "cmpw %%ax, %%bx\n\t"
> 			      "je 2f\n\t"
> 			      "rep ; nop\n\t"
- 			      "movw %1, %%bx\n\t"
+ 			      "movw %1, %%ax\n\t"
> 			      "lfence\n\t"
> 			      "jmp 1b\n\t"
> 			      "2:\n\t"
> 			    : "+m" (*(int *) lock)
> 			    : "m" (lock[0]), "a" (0x10000) : "ebx", "memory");
> }

Erm, modulo that bugger ;) that'd never should up in the non-contended 
case (and that does not change numbers):

inc-lock in cache takes 7.28ns
xadd-lock in cache takes 8.93ns
vadd-lock in cache takes 10.34ns
zadd-lock in cache takes 8.43ns
inc-lock out of cache takes 87.98ns
xadd-lock out of cache takes 88.89ns
vadd-lock out of cache takes 89.59ns
zadd-lock out of cache takes 89.86ns



- Davide


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