* Colin Fowler <[EMAIL PROTECTED]> wrote:
> > and context-switches 45K times a second. Do you know what is going
> > on there? I thought ray-tracing is something that can be
> > parallelized pretty efficiently, without having to contend and
> > schedule too much.
>
> This is a RTRT (real-time ray tracing) system and as a result differs
> from traditional offline ray-tracers as it is optimised for speed. The
> benchmark I ran while these data were collected renders an 80K polygon
> scene to a 512x512 buffer at just over 100fps.
>
> The context switches are most likely caused by the pthreads
> synchronisation code. There are two mutexs. Each job is a 32x32 tile
> and each mutex is therefore unlocked (512/32) * (512/32) * 100 (for
> 100fps) * 2 =~50k. There's very likely where our context switches are
> coming from. Larger tile sizes would of course reduce the locking
> overhead, but then the ray-tracer suffers form load imbalance as some
> tiles are much quicker to render than others. Empircally we've found
> that this tile-size works the best for us.
>
> The CPU idling occurs as the system doesn't yet perform asynchronous
> rendering. When all tiles in a current job queue are finished the
> current frame is done. At this point all worker threads sleep while
> the master thread blits the image to the screen and fills the job
> queue for the next frame. The data probably shows that one CPU is kept
> maxed and the others reach about 90% most of the time. This is
> something on my TODO list to fix along with a myriad of other
> optimisations :)
is this something i could run myself and see how it behaves with various
scheduler settings? (if yes, where can i download it and is there any
sample scene that would show similar effects.)
Ingo
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