Subject: Re: TLB entries > 4kb

From: David Woodhouse <[email-masked]>
Date: Thu, 12 Feb 1998 21:52:19 +0000

[email-masked] said:
> On Thu, 12 Feb 1998, Alan Cox wrote:
> > On the intel its a huge win to map PCI frame buffers using 4Mbyte pages, but
> > the kernel mmap really can't hack the idea right now. A pity cos if you
> > hack it in and make sure you never unmap it you get 2-3% better X 
> > performance
> 
> i tried to hack this half a year ago, but had to find out that 4MB pages
> are only valid for kernel mappings, which means we'd have to make X a ring
> 0 process too ...

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[email-masked] said:
>  The way its done is ok normally. I guess you need to make X over
> Linux/RT call the rtlinux kernel to handle it. Note X _has_ to do
> those global cli/sti's to meet hardware needs

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GGI (well, KGI) should be able to fix both of these, shouldn't it?

----                              ----                              ----
David Woodhouse, Robinson College, CB3 9AN, England.   (+44) 0976 658355
    [email-masked]        http://dwmw2.robinson.cam.ac.uk
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From: [email-masked] (Alan Cox)
Date: Thu, 12 Feb 1998 21:57:07 +0000 (GMT)

> GGI (well, KGI) should be able to fix both of these, shouldn't it?

Not for Linux/RT - the kernel cant do real cli/sti pairs. The stuff
would have to become an RTLinux graphics setup call set

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From: MOLNAR Ingo <[email-masked]>
Date: Thu, 12 Feb 1998 23:00:09 +0100 (CET)

> GGI (well, KGI) should be able to fix both of these, shouldn't it?

the hw virtualization (cli/sti) thing yes, but the 4MB thing not, as
GGILib lives in user-space, GGI does not spend too much time in the
kernel, rendering is done in user-space.

but i suspect things doing direct rendering like Quake could benefit from
4MB pages big time. For this we have to implement ring-0 processes though
... XFree86 is nicely accelerated (and the accelerator chip has no
business with the CPU).

-- mingo