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. 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'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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