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From: Zachary Amsden <zach@vmware.com>
To: Andi Kleen <ak@suse.de>
Cc: akpm@osdl.org, chrisl@vmware.com, chrisw@osdl.org, hpa@zytor.com,
	Keir.Fraser@cl.cam.ac.uk, linux-kernel@vger.kernel.org,
	m+Ian.Pratt@cl.cam.ac.uk, mbligh@mbligh.org, pratap@vmware.com,
	virtualization@lists.osdl.org, zwame@arm.linux.org.uk
Subject: Re: [PATCH 5/14] i386 / Use early clobber to eliminate rotate in desc
Date: Tue, 16 Aug 2005 16:56:16 -0700	[thread overview]
Message-ID: <43027D20.7020907@vmware.com> (raw)
In-Reply-To: <20050816234514.GG27628@wotan.suse.de>

Andi Kleen wrote:

>On Wed, Aug 10, 2005 at 09:54:11PM -0700, zach@vmware.com wrote:
>  
>
>>Use an early clobber on addr to avoid the extra rorl instruction at the
>>end of _set_tssldt_desc.
>>    
>>
>
>I would suggest to just use C for this. I do this on x86-64 and 
>I don't think there is any reason to use this hard to maintain
>code for it.
>

This one in particular is non-optimal looking from C because the 
compiler misses the potential for rotation.  But, composing into 
temporaries and then issuing two writes to memory instead of multiple 
writes within the same word could actually get you a better cycle count, 
and that is something GCC just might be able to do :)

Zach

  reply	other threads:[~2005-08-16 23:56 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-08-11  4:54 [PATCH 5/14] i386 / Use early clobber to eliminate rotate in desc zach
2005-08-16 23:45 ` Andi Kleen
2005-08-16 23:56   ` Zachary Amsden [this message]
2005-08-17  0:06     ` H. Peter Anvin
2005-08-17 14:22       ` Alan Cox
2005-08-17 15:54         ` H. Peter Anvin

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