linux-kernel - Re: [PATCH] x86: Extend test_and_set_bit() test_and_clean_bit() to 64 bits in X86

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Message-ID: <20090514142749.GE10933@one.firstfloor.org>
Date:	Thu, 14 May 2009 16:27:49 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] x86: Extend test_and_set_bit() test_and_clean_bit() to 64 bits in X86_64

On Thu, May 14, 2009 at 07:16:10AM -0700, H. Peter Anvin wrote:
> Andi Kleen wrote:
> >>>
> >> The right way to do it is to pass the proper type of register.
> > 
> > For the input index register you don't actually need 64bit and for the
> > value it's typically memory anyways.
> > 
> 
> If you have a 64-bit operation you have a 64-bit index register.  And
> you need a 64-bit index for it to handle over 2^31 (since it is signed.)

Pretty much all the bit ops and a few other operations currently have
2/4GB limits on x86-64. I don't think that's going to change.

In the kernel nothing is ever that big continuously anyways.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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