Re: iBook and playing DVDs
>On Wed, 2002-05-22 at 21:48, benh@kernel.crashing.org wrote:
>> >What about a mixed approach to avoid unnecessary bus traffic: try to read
>> >the ring head pointer from memory, and if after a timeout the free
>ring space
>> >still doesn't seem to be large enough, read it directly from the register.
>> >This could hurt performance badly if the memory copy is often outdated
>> though.
>>
>> Well, let's first make it stable...
>
>Good idea. :) Do you agree with Albert's analysis? Have you tried with
>caching enabled yet?
Albert analysis makes sense, though I tried a different approach which
was to set the Guarded bit on the BAT mapping. Well, anyway, I'll do some
experiments with that again when I have less pressure from work, I can
at least try to find some more infos about what's going on in the card
when the CCE stops.
>
>> >> >If apps would at least avoid reading stuff written
>> >> >by the video card, write-through cached would be OK.
>> >> >Apps that read AGP memory are uncommon enough that
>> >> >fixing all of them would be feasible.
>> >>
>> >> I think we can use full caching (copyback) without too much
>> >> problems. In the r128 case, we'll have to flush from the X server
>> >> as it's directly writing to the ring (and maybe from the mesa driver
>> >> as well). On radeon, it's all done via indirect buffers and those
>> >> get passed to the kernel driver before beeing inserted in the ring.
>> >
>> >Where is r128 different than radeon in this respect?
>>
>> The last time I looked at r128, it wrote to the ring directly iirc,
>> while radeon on wrote to indirect buffers, the kernel putting them
>> in the ring. This may have changed though.
>
>I'm pretty sure only the kernel ever had access to the ring in both
>drivers (the only exception I know of were the ati-5-0-[01] branches in
>DRI CVS, but they were never merged into the trunk, let alone an XFree86
>release).
Ok, my memory may be failing here ;)
Ben.
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