On Mon, 22 Sep 2003, Ian Romanick wrote:
> Mark Vojkovich wrote:
>
> > Can we export to the drivers some function that yields the CPU?
> > Currently alot of drivers burn the CPU waiting for fifos, etc...
> > usleep(0) is not good for this because it's jiffy based and usually
> > never returns in less than 10 msec which has the effect of making
> > interactivity worse instead of better. I'm not sure which platforms
> > don't export sched_yield() and which will need alternative
> > implementations.
>
> There was a thread about this on the dri-devel list some months ago.
> The short answer is DON'T DO IT! :) I don't think that sched_yield will
> give the desired results in the 2D driver any more than it does in the
> 3D driver. I *believe* that there is another function for this purpose,
> but I can't recall what it is called.
>
> http://marc.theaimsgroup.com/?l=dri-devel&m=105425072210516&w=2
> http://lwn.net/Articles/31462/
Currently, sched_yield() *does* give the desired result and I have
used it with great success in many places, XvMC drivers in particular.
Issues with specific implementations of sched_yield() with recent
Linux kernels does not change the need to yield. Driver yields will
not be random and usleep is unusable because of it's jiffy nature.
It sounds like the Linux 2.5 implementation is less desirable than
the Linux 2.4 implementation, however, in lieu of an alternative,
it is still better than burning the entire slice waiting for the
fifo to drain. The ability to yield is essential with DMA based
user-space drivers. These drivers can queue up alot of work and
often have to wait a long time before they can continue.
The fact that there may be different best implementations
with various kernels only further supports that XFree86 should
export a xf86Yield() function which "does the right thing" on
that platform. For Linux <= 2.4 that appears to be sched_yield().
I don't know about the other OSes though, which is why I brought
this up on this list.
Mark.
_______________________________________________
Devel mailing list
[EMAIL PROTECTED]
http://XFree86.Org/mailman/listinfo/devel
