[please cc me, I'm not on the dri list]
On Fri, 2004-08-20 at 22:29, Jon Smirl wrote:
> The delay is very large because this routine is waiting for the
> graphics coprocessor to finish an operation. Some of the operations can
> take many ms to complete; for example telling the chip to copy 64MB of
> memory somewhere.
That corresponds to my experience. I currently use glxgears while
running low latency audio stuff to test whether the problem is there or
not. For small window sizes (of glxgears) everything is fine. If I keep
making the window bigger there is a point where I start triggering xruns
like crazy (7 to 10 msecs or so).
> I would think the question should be, how do we wait
> on the GPU without killing both audio and video latency.
>
> The problem here is that most graphics commands are very short in
> duration. Some of these commands can be issued a million of times per
> second. A few commands are much longer running. I don't believe there
> is an easy way to tell how long the commands will run.
>
> A better solution might be to loop twenty times to pick up the very
> short commands. After 20us switch to a loop that allows the kernel to
> schedule. You don't want to immediately schedule since that will kill
> graphics performance.
What would be a good program that measures graphics performance that I
could run to test this? I could build a kernel with a patch I have that
has conditional reschedules in it (but it is illegal in the sense that
reschedules with a lock held) and see how that impacts performance, or
not. But I need something to test that will reflect some metric that
makes sense to the graphics crowd.
-- Fernando
> What's the right way to write a loop like this that meets the above
> requirements and also satisfies the audio needs?
>
>
> static int radeon_do_wait_for_idle( drm_radeon_private_t *dev_priv )
> {
> int i, ret;
>
>
> dev_priv->stats.boxes |= RADEON_BOX_WAIT_IDLE;
>
>
> ret = radeon_do_wait_for_fifo( dev_priv, 64 );
> if ( ret ) return ret;
>
>
> for ( i = 0 ; i < dev_priv->usec_timeout ; i++ ) {
> if ( !(RADEON_READ( RADEON_RBBM_STATUS )
> & RADEON_RBBM_ACTIVE) ) {
> radeon_do_pixcache_flush( dev_priv );
> return 0;
> }
> DRM_UDELAY( 1 );
> }
>
>
> #if RADEON_FIFO_DEBUG
> DRM_ERROR( "failed!\n" );
> radeon_status( dev_priv );
> #endif
> return DRM_ERR(EBUSY);
> }
>
> =====
> Jon Smirl
> [EMAIL PROTECTED]
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