diff options
| -rw-r--r-- | src/mesa/drivers/dri/i965/brw_urb.c | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_urb.c b/src/mesa/drivers/dri/i965/brw_urb.c index 1a004176de1..5cc51ad4ec4 100644 --- a/src/mesa/drivers/dri/i965/brw_urb.c +++ b/src/mesa/drivers/dri/i965/brw_urb.c @@ -42,7 +42,44 @@ #define SF 3 #define CS 4 -/* XXX: Are the min_entry_size numbers useful? +/** @file brw_urb.c + * + * Manages the division of the URB space between the various fixed-function + * units. + * + * See the Thread Initiation Management section of the GEN4 B-Spec, and + * the individual *_STATE structures for restrictions on numbers of + * entries and threads. + */ + +/* + * Generally, a unit requires a min_nr_entries based on how many entries + * it produces before the downstream unit gets unblocked and can use and + * dereference some of its handles. + * + * The SF unit preallocates a PUE at the start of thread dispatch, and only + * uses that one. So it requires one entry per thread. + * + * For CLIP, the SF unit will hold the previous primitive while the + * next is getting assembled, meaning that linestrips require 3 CLIP VUEs + * (vertices) to ensure continued processing, trifans require 4, and tristrips + * require 5. There can be 1 or 2 threads, and each has the same requirement. + * + * GS has the same requirement as CLIP, but it never handles tristrips, + * so we can lower the minimum to 4 for the POLYGONs (trifans) it produces. + * We only run it single-threaded. + * + * For VS, the number of entries may be 8, 12, 16, or 32 (or 64 on G4X). + * Each thread processes 2 preallocated VUEs (vertices) at a time, and they + * get streamed down as soon as threads processing earlier vertices get + * theirs accepted. + * + * Each unit will take the number of URB entries we give it (based on the + * entry size calculated in brw_vs_emit.c for VUEs, brw_sf_emit.c for PUEs, + * and brw_curbe.c for the CURBEs) and decide its maximum number of + * threads it can support based on that. in brw_*_state.c. + * + * XXX: Are the min_entry_size numbers useful? * XXX: Verify min_nr_entries, esp for VS. * XXX: Verify SF min_entry_size. */ |