回复： 回复： Where does Xorg fallbackto ?

[小飞珑]

You didn't help about my question, and did not answer where the fbCopyNtoN and fbCopyArea hide. I shall repeat my simple and  humble question again : are the fbCopyNtoN() and fbCopyarea() in UXA implemented in Xorg fb/fbcopy? 



------------------ 原始邮件 ------------------
发件人: "Chris Wilson";<chris at chris-wilson.co.uk>;
发送时间: 2013年9月23日(星期一) 下午5:40
收件人: "小飞珑"<404962885 at qq.com>; 
抄送: "xorg-devel"<xorg-devel at lists.x.org>; 
主题: Re:  回复： Where does Xorg fallbackto ?



On Mon, Sep 23, 2013 at 05:13:19PM +0800, 小飞珑 wrote:
>    The right answer is don't start from there. For fallbacks, UXA uses a
>    GTT mapping so every surface is actually in WC memory - every read is
>    treated as uncached, and fallbacks do a lot of reads. Effort spent
>    optimising the fb layer in this case is completely wasted.
>    -Chris
> 
>      I don't quite understand that. Or you mean that  fbCopyArea() is
>    wrapped?

The fb* functions are provided by the xserver. What I am trying to point
out is that UXA fundamentally uses hw in such a way that prevents
optimisation. Every pointer read in fb* is uncached. Optimising an
already fairly well optimised implementation will at most gain less than
a percent overall. Switching to a different mapping and implementating
migration will gain an order of magnitude performance improvement.
Implementing 2D acceleration will gain between 5x-10x over and above the
optimal fb implementation.

If you read the driver more carefully you will find these answers
already there.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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