linux-kernel - Re: [PATCH 3/4, v2] x86: enlightenment for ticket spin locks

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Date:	Wed, 30 Jun 2010 10:13:12 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	jeremy.fitzhardinge@...rix.com, mingo@...e.hu, tglx@...utronix.de,
	Ky Srinivasan <KSrinivasan@...ell.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4, v2] x86: enlightenment for ticket spin locks -	 eliminate
 NOPs introduced by first patch

On 06/30/2010 12:07 AM, Jan Beulich wrote:
>>
>> If you're stretching (bloating) them anyway, perhaps we should be using
>> "add" instructions instead, with their better EFLAGS behavior?
> 
> Hmm, yes, that possibility I didn't even consider. Would have
> the potential to get away without that admittedly ugly "unary"
> assembler macro altogether, though at the price of growing all
> instructions rather than just those that have a non-symbolic
> and small displacement. Since unlock generally gets inlined, I'm
> not certain this additional growth in code size would be
> acceptable...
> 
> Please let me know, though before submitting an eventual third
> version I'd appreciate knowing especially the first two patches
> need further changes in order to get accepted.
> 

Will look at it today, hopefully.  The Syslinux 4.00 release has
unfortunately occupied me over the last week-plus.

As far as the "unary" macro is concerned... I have to admit I couldn't
even figure out what it was supposed to do.  It could definitely use a
better comment.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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