linux-kernel - Re: [PATCH 1/2] bitreversal program

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Message-ID: <20080520163912.GP7567@pirzuine>
Date:	Tue, 20 May 2008 18:39:12 +0200
From:	Benoit Boissinot <bboissin@...il.com>
To:	Soumyadip Das Mahapatra <kernelhacker@...ualserver.org>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] bitreversal program

On Tue, May 20, 2008 at 05:57:37PM +0200, Soumyadip Das Mahapatra wrote:
> On Tue, 20 May 2008, Benoit Boissinot wrote:
>> On Tue, May 20, 2008 at 5:25 PM, Soumyadip Das Mahapatra
>> <kernelhacker@...ualserver.org> wrote:
>>> I know that my bitrev8() takes more instructions than that
>>> of yours. But we have to think about faster access of cpu cache over that
>>> of memory cache(which your bit_rev_table uses).
>>
>> I didn't review your patch, sorry.
>> But I'm pretty sure that your patch won't be considered unless you
>> provide benchmarks
>> with numbers for different CPU/architecture.
>> Ideally you should provide a script to test the correctness and the
>> performance of your
>> change that anyone could run on his computer.
>
> Thanks Benoit for giving me such a precious advice. But sorry, I dont
> have any benchmarking system in my hand(how can i have? i am just a
> student, not a professional).
> So if you do me a favour and kindly do it for me, please :-)

A quick benchmarking (that you should have done at least one your
computer gives for 100000000 iterations):
old:
real	0m1.631s
user	0m1.628s
sys	0m0.004s

new:
real	0m5.553s
user	0m5.540s
sys	0m0.004s

So I guess there's no need to discuss this further.

regards,

Benoit

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