linux-kernel - Re: [RFC] fbdev/riva:change to use generice function to implement reverse

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Date:	Mon, 24 Aug 2015 19:11:48 +0530
From:	Afzal Mohammed <afzal.mohd.ma@...il.com>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>, adaplas@...il.com,
	plagnioj@...osoft.com, linux-fbdev@...r.kernel.org,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] fbdev/riva:change to use generice function to implement
 reverse_order()

Hi,

On Mon, Aug 24, 2015 at 04:31:13PM +0800, yalin wang wrote:
> 
> i only submit the bit reverse patch for arm / arm64 arch,

yes, saw later git blaming it on you :)

> > Not for this case, but once measured on ARM, iirc, a 32-bit asm bit
> > reversal as compared to doing it in C was taking 1 cycle as opposed to
> > ~225 cycles!, of course writing optimized C could have made it fare
> > better, but still would reach no-way near asm bit reversal.

The above measurement was done not in Linux, rather on a baremetal
code, but seeing the efficient Kernel C implementation, realized that
the gain would not be that much, it would be good to know if there are
measurements for Kernel bitreversal in C & asm (on supported arch)

Regards
afzal
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