Erwin Rol wrote:
>
>
> First of all for our RT-Linux/RTAI maintainers, i would sugest
> to make parts of this thread a very big point in the FAQ, i lost
> lot of time with something that was apparently a known problem.
> Also a black list with devices that cause problems and a white list
> with devices that have no known problems wouldn't be bad.
>
> One big quiestion remains , what is so different in XFree 4.0.1
> compared to XFree 3.3.6 ?! the s3virge driver in 3.3.6 isn't (much)
> slower
> than in 4.0.1 , but the latency is gone. The mga driver is slower but
> here
> also the latency is gone when using 3.3.6. The structure of XFree 4.0.1
> gives us the posibility to patch the drivers when needed and only
> distribute
> those, that way there could be made lowlatency version of the drivers
> without the
> need for ppl to download multi mega byte tar/rpm files. (just like is
> done
> with the patches for the linux kernel )
>
I suppose we could add an option, something like 'early_sync' (or maybe
something more descriptive) which changes the accelerator sync behavior
in 4.0.x drivers to make them behave more like 3.3.6. I'd be willing to
make a trial s3virge driver with a change like this so you could test
it.
Mark,
I'm thinking of adding AccelSync commands to all the Subsequent
accelerated primitives and enabling them on an option. That should get
us close to the 3.3.6 architecture in a switchable way.
All,
Although maybe we should be asking a more general question. Is 3.3.6
(or a 3.3.6 architecture) really going to meet your latency requirements
in all cases? If the accelerator can cause this problem in 4.0.x, it is
entirely possible that 3.3.6 has the problem also, but because it
doesn't pack the accel. FIFO as efficiently, it is harder to see failing
cases.
>From a design standpoint, how are you going to guarantee your hard real
time numbers? (Which leads back to my suggestion of not running X on a
hard real time system, at least with these particular S3 & Matrox
cards.)
Kevin
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