Performance Results

F3DEX3_NOC matches or beats the RSP performance of F3DEX2 on all critical paths in the microcode, including command dispatch, vertex processing, and triangle processing. Then, the RDP and memory traffic performance improvements of F3DEX3–56 vertex buffer, auto-batched rendering, etc.–should further improve overall game performance from there.

Cycle Counts

These are cycle counts for many key paths in the microcode. Lower numbers are better. The timings are hand-counted taking into account all pipeline stalls and all dual-issue conditions. Instruction alignment after branches is usually taken into account (especially in F3DEX3), but in some cases it is assumed to be optimal.

All numbers assume default profiling configuration. Tri numbers assume texture, shade, and Z, and not flushing the buffer. Tri numbers are measured from the first cycle of the command handler inclusive, to the first cycle of whatever is after $ra exclusive; this is in order to capture an extra stall cycle in F3DEX2 when finishing a triangle and going to the next command.

Vertex numbers assume no extra F3DEX3 features (packed normals, ambient occlusion, etc.). These features are listed below as the number of extra cycles the feature costs per vertex pair. ltbasic is the codepath when point lighting, specular, and Fresnel are disabled; ltadv is the codepath with any of these enabled. The reason timings are listed separately for each number of lights is because some implementations are pipelined for two lights, so going from an even to an odd number of lights adds a different time than vice versa.

	F3DEX2	F3DEX3_NOC	F3DEX3
Command dispatch	12	10	10
Small RDP command	14	4	4
Only/2nd tri to offscreen	27	20	20
1st tri to offscreen	28	21	21
Only/2nd tri to clip	32	25	25
1st tri to clip	33	26	26
Only/2nd tri to backface	38	31	31
1st tri to backface	39	32	32
Only/2nd tri to degenerate	42	33	33
1st tri to degenerate	43	34	34
Only/2nd tri to occluded	Can't	Can't	37
1st tri to occluded	Can't	Can't	38
Only/2nd tri to draw	172	149	151
1st tri to draw	173	150	152
Tri snake	Can't	10/11*	10/11*
Vtx before DMA start	16	17	17
Vtx pair, no lighting	54	54	70
Vtx pair, 0 dir lts	Can't	65	81
Vtx pair, 1 dir lt	73	70	86
Vtx pair, 2 dir lts	76	77	93
Vtx pair, 3 dir lts	88	84	100
Vtx pair, 4 dir lts	91	91	107
Vtx pair, 5 dir lts	103	98	114
Vtx pair, 6 dir lts	106	105	121
Vtx pair, 7 dir lts	118	112	128
Vtx pair, 8 dir lts	Can't	119	135
Vtx pair, 9 dir lts	Can't	126	142
Vtx pair, 0 point lts	Can't	117	133
Vtx pair, 1 point lt	276	194	210
Vtx pair, 2 point lts	420	271	287
Vtx pair, 3 point lts	564	348	364
Vtx pair, 4 point lts	708	425	441
Vtx pair, 5 point lts	852	502	518
Vtx pair, 6 point lts	996	579	595
Vtx pair, 7 point lts	1140	656	672
Vtx pair, 8 point lts	Can't	733	749
Vtx pair, 9 point lts	Can't	810	826
Packed normals, ltbasic	Can't	6	6
Light-to-alpha, ltbasic	Can't	10	10
Ambient occlusion, ltbasic	Can't	9	9
Packed normals, ltadv	Can't	-3	-3
Light-to-alpha, ltadv	Can't	6	6
Ambient occlusion, ltadv	Can't	0	0
Specular or fresnel	Can't	47	47
+ Fresnel	Can't	23	23
+ Specular per dir lt	Can't	13	13
+ Specular per point lt	Can't	13	13
Light dir xfrm, 0 dir lts	Can't	92	92
Light dir xfrm, 1 dir lt	141	92	92
Light dir xfrm, 2 dir lts	180	93	93
Light dir xfrm, 3 dir lts	219	118	118
Light dir xfrm, 4 dir lts	258	119	119
Light dir xfrm, 5 dir lts	297	144	144
Light dir xfrm, 6 dir lts	336	145	145
Light dir xfrm, 7 dir lts	375	170	170
Light dir xfrm, 8 dir lts	Can't	171	171
Light dir xfrm, 9 dir lts	Can't	196	196

Triangle Snake Cycle Counts

With the recent F3DEX3 updates bringing significant RSP time savings in command dispatch and triangle draw, triangle snakes are unfortuantely no longer competitive in RSP time.

Suppose we have two tris which are offscreen. If drawn with SP2Triangles, this is 10 cycles for command dispatch, 21 cycles to cull the first tri, and 20 cycles to cull the second, for a total of 51 cycles. If drawn as part of a long triangle snake, the triangle snake processing adds 10 or 11 cycles relative to the SP2Triangles first or second triangle respectively. So this is 31 cycles to cull each triangle, for a total of 61 cycles.

It gets worse for snakes when counting the overhead of starting and ending a snake, which have also gotten worse with the recent changes bringing triangle performance improvements. I used to have a long discussion here computing estimated performance for switching to snakes, but the numbers have all changed and they were imprecise to begin with. The upshot is for a typical scene, switching everything from SP2Triangles to snakes might save about 70 us of RDRAM/RDP time but cost about 400 us of RSP time.

However, note that in F3DEX2, SP2Triangles to two offscreen triangles is 12+28+27 = 67 cycles. F3DEX3 is so much faster than F3DEX2 that even the performance penalty of snakes doesn't outweigh this.