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

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Date:	Fri, 21 Aug 2015 11:01:41 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	yalin wang <yalin.wang2010@...il.com>
CC:	<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()



On 21/08/15 10:46, yalin wang wrote:

>>> i investigate on arm64 platforms:
>>
>> Ok. So is any arm64 platform actually using these devices? If these
>> devices are mostly used by 32bit x86 platforms, optimizing them for
>> arm64 doesn't make any sense.
>>
>> Possibly the patches are still good for x86 also, but that needs to be
>> proven.
>>
> not exactly, because x86_64 don’t have hardware instruction to do rbit OP,
> i compile by test :

For old drivers i386 may be more relevant than x86_64.

So you don't have the actual HW?

These kind of optimizations should have some real world measurements,
not just compiling, looking at the assembly and guessing whether it's
faster or not.

 Tomi


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