linux-kernel - Re: [PATCH 3/3] 64-bit futexes: x86 support

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Date:	Fri, 30 May 2008 19:25:06 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ulrich Drepper <drepper@...hat.com>
cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mtk.manpages@...il.com
Subject: Re: [PATCH 3/3] 64-bit futexes: x86 support



On Fri, 30 May 2008, Ulrich Drepper wrote:
>
> +#ifdef CONFIG_X86_32
> +	/* Not all 32-bit machines support 8-byte cmpxchg.  We just
> +	   unconditionally perform a runtime check for the feature.  */
> +	if ((op & FUTEX_FLAG_64) && !boot_cpu_has(X86_FEATURE_CX8))
> +		return -ENOSYS;
> +#endif

Also, doesn't this mean that effectively you have given up on any CPU 
before the Pentium entirely? 

Not that I want to take the patches _anyway_, but it seems doubly stupid. 
Those things are going to be UP machines, so you could have just emulated 
it with no correctness issues by disabling preemption.

		Linus
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