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From: Arjan van de Ven <arjan@linux.intel.com>
To: Chinmay V S <chinmay.v.s@pathpartnertech.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
	linux-kernel@vger.kernel.org, cvs268@gmail.com,
	tglx@linutronix.de, jeff.chua.linux@gmail.com
Subject: Re: [RFC] [PATCH] [timer] Optimise apply_slack() for size and speed.
Date: Fri, 03 Feb 2012 06:52:23 -0800	[thread overview]
Message-ID: <4F2BF4A7.2070603@linux.intel.com> (raw)
In-Reply-To: <CAKZbaaTDcfEVPa2JRSnkv_YCiScoTTqpmzaGQGWT98QJpYzZ8A@mail.gmail.com>

On 2/2/2012 10:31 PM, Chinmay V S wrote:
> Here is the dis-assembly (build for x86) :
> 
> Original code snippet :
> mov    %eax,%ecx
> mov    $0x1,%edx
> shl    %cl,%edx
> sub    $0x1,%edx
> mov    %edx,-0x10(%ebp)
> not    %edx
> and    %esi,%edx
> mov    %edx,-0x14(%ebp)
> 
> Patched code snippet :
> mov    %eax,%ecx
> shrl   %cl,-0x14(%ebp)
> shll   %cl,-0x14(%ebp)
> 
> As is evident, we are able to reduce 5 instructions by using a bit-shift
> logic (compared to a masking logic).
> 

this code is so not performance critical to this level, that we should
optimize for readability, not for the output of a compiler.



      parent reply	other threads:[~2012-02-03 14:52 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-31  9:37 [RFC] [PATCH] [timer] Optimise apply_slack() for size and speed Chinmay V S
2012-02-02 22:59 ` Sebastian Andrzej Siewior
     [not found]   ` <CAKZbaaTDcfEVPa2JRSnkv_YCiScoTTqpmzaGQGWT98QJpYzZ8A@mail.gmail.com>
2012-02-03 14:52     ` Arjan van de Ven [this message]

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