Re: Xvideo acceleration: GATOS for PPC?
Hi Michel,
On 29 Aug, this message from Michel Dänzer echoed through cyberspace:
>> > > > Although I found no evidence documented evicende of this, I suppose
>> > > > this is because XFree (plain), although implementing Xvideo, doesn't
>> > > > use the hardware acceleration in the ATI chips, whereas the GATOS
>> > > > drivers do just that.
>> > >
>> > > Not quite. Plain XFree86 uses the frontend scaler, which also does the
>> > > colorspace conversion. The reason for the CPU load is that the data is
>> > > transferred to the card with regular memcpy. If the GATOS drivers use
>> > > (virtually) no CPU for the transfer, that hints at that they use bus
>> > > mastering for the transfer. Very interesting, I'll have to look at the
>> > > code.
>> >
>> > False alarm, they also use memcpy. In fact, the code looks very similar to
>> > plain XFree86, so I'd be surprised if it makes any difference.
>>
>> Did you look at the r128 driver only? My test showing the decrease in CPU
>> load was on a Rage Mobility-equipped Dell laptop (i.e Mach64-compatible
>> using the ati driver).
>
> Nope, I looked at the mach64 code as well. Looks like slightly modified r128
> code. The only real difference seems to be that GATOS supports additional
> video chips, but that doesn't apply to us.
Hmmm..... strange, then. I tried the GATOS drivers on my TiBook (with
Josh's fix -- thanks), but they give the same performance as the
standard one, plus a (probably) endianess bug: they seem to 'reverse'
successive image blocks on screen; probably 4- or 8-pixel-wide blocks...
To sum up my performance comparisons so far, all with XFree 4.1.0 from
unstable, and vlc 0.2.83:
- Mach64/i386 without GATOS: no Xvideo (driver is broken); vlc uses 45%
+ 16% cpu (two 'consuming' threads); X uses 25% cpu.
- Mach64/i386 with GATOS driver: Xvideo works, vlc uses 25% (other
threads insignificant), X uses between 2% and 5%
- Voodoo3/i386: Xvideo works, X around 25% and vlc around 30% (roughly)
- Rage128/ppc: Xvideo works, X between 10% and 20%, rest consumed by
vlc.
The Mach64 is on a Dell laptop w/ Celeron 600, the Voodoo is a PIII/666
desktop, and the ppc is my TiBook/400.
So the question is: why does X on the Dell use so little CPU, and why
can't we achieve the same thing on ppc (the Voodoo was for comparison
only)?
Michel
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