drm/amdkfd: Fix signal handling performance again

It turns out that idr_for_each_entry is really slow compared to just
iterating over the slots. Based on measurements the difference is
estimated to be about a factor 64. That means using idr_for_each_entry
is only worth it with very few allocated events.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>

drivers/gpu/drm/amd/amdkfd/kfd_events.c

@@ -496,7 +496,7 @@ void kfd_signal_event_interrupt(unsigned int pasid, uint32_t partial_id,
 			pr_debug_ratelimited("Partial ID invalid: %u (%u valid bits)\n",
 					     partial_id, valid_id_bits);
 
-		if (p->signal_event_count < KFD_SIGNAL_EVENT_LIMIT/2) {
+		if (p->signal_event_count < KFD_SIGNAL_EVENT_LIMIT / 64) {
 			/* With relatively few events, it's faster to
 			 * iterate over the event IDR
 			 */