回复： Where does Xorg fallback to ?

[小飞珑]

------------------ 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4:03
收件人: "小飞珑"<404962885 at qq.com>; 
抄送: "xorg-devel"<xorg-devel at lists.x.org>; 
主题: Re: Where does Xorg fallback to ?



On Mon, Sep 23, 2013 at 10:45:41AM +0800, 小飞珑 wrote:
>      Hi,
>       I am looking into Xorg for performance optimization, and want to do
>    some software acceleration for the Xorg fallback functions when the
>    hardware acceleration is not available. I am now using a notebook with
>    intel display card. In the UXA driver, I force the driver to use fallback
>    funcs instead of the Accelerated funcs. As in uxa/uxa-accel.c ->
>    uxa_copy_area(), I made uxa_screen->force_fallback = 1, force uxa driver
>    to call uxa_check_copy_area()->fbCopyArea(), but the fbCopyArea seemed NOT
>    to be the fbCopyArea in Xorg fb/fbcopy.c ! For I added return NULL
>    immediately  in the beginning of fb/fbcopy.c -> fbCopyArea(), but made no
>    difference, but if I comment the fbCopyArea() in uxa/uxa-unaccel.c the
>    display is ruined. It seemed that the above two fbCopyArea() functions are
>    not the same. Where did the Xorg fallback to? NOT to the fb/fbcopy.c ? I
>    am eager to know that, could some body tell ? Thanks a lot!

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 problem of mine is that I did not find the realization source code of fbCopyArea or fbCopyNtoN in UXA driver, might you pointed them out for me ? That might be a start after all.
  Or might I ask what you would suggest for a potential optimization for fallbacks of Xorg?
-- 
Chris Wilson, Intel Open Source Technology Centre
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