Now We CAD

Perf Must Increase.

After my last post, I’m sure everyone was speculating about the forthcoming zink takeover of the CAD industry. Or maybe just wondering why I’m bothering with this at all. Well, the answer is simple: CAD performance is all performance. If I can improve FPS in viewperf, I’m decreasing CPU utilization in all apps, which is generally useful.

As in the previous post, the catia section of viewperf was improved to a whopping 34fps against the reference driver (radeonsi) by eliminating a few hundred thousand atomic operations per frame. An interesting observation here is that while eliminating atomic operations in radeonsi does improve FPS there by ~5% (105fps), there is no bottlenecking, so this does not “unlock” further optimizations in the same way that it does for zink. I speculate this is because zink has radv underneath, which affects memory access across ccx in ways that do not affect radeonsi.

In short: a rising tide lifts all ships in the harbor, but since zink was effectively a sunken ship, it is rising much more than the others.

Even More Improvements

Since that previous post, I and others have been working quietly in the background on other improvements, all of which have landed in mesa main already:

A nice 35% improvement, largely from three MRs:

That’s right. In my quest to maximize perf, I have roped in veteran radv developer and part-time vacation enthusiast, Samuel Pitoiset. Because radv is slow. vkoverhead exists to target noticeably slow cases, and by harnessing the forbidden power of rewriting the whole driver, it was possible for a lone Frenchman to significantly reduce bottlenecking during draw emission.

This Isn’t Even My Final Form

Obviously. I’m not about to say that I’ll only stop when I reach performance parity, but the FPS can still go up.

At this point, however, it’s becoming less useful (in zink) to look at flamegraphs. There’s only so much optimization that can be done once the code has been simplified to a certain extent, and eventually those optimizations will lead to obfuscated code which is harder to maintain.

Thus, it’s time to step back and look architecturally. What is the app doing? How does that reach the driver? Can it be improved?

GALLIUM_TRACE is a great tool for this, as it logs the API stream as it reaches the backend driver, and there are parser tools to convert the output XML to something readable. Let’s take a look at a small cross-section of the trace:

pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10043], [is_user_buffer = 0, buffer_offset = 7440, buffer.resource = resource_10043]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10044], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10045], [is_user_buffer = 0, buffer_offset = 7632, buffer.resource = resource_10045]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10046], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10047], [is_user_buffer = 0, buffer_offset = 7680, buffer.resource = resource_10047]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10048], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10049], [is_user_buffer = 0, buffer_offset = 7656, buffer.resource = resource_10049]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10050], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10051], [is_user_buffer = 0, buffer_offset = 7752, buffer.resource = resource_10051]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10052], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10053], [is_user_buffer = 0, buffer_offset = 7800, buffer.resource = resource_10053]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10054], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10055], [is_user_buffer = 0, buffer_offset = 7968, buffer.resource = resource_10055]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10056], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10057], [is_user_buffer = 0, buffer_offset = 7968, buffer.resource = resource_10057]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10058], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10059], [is_user_buffer = 0, buffer_offset = 8136, buffer.resource = resource_10059]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10060], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10061], [is_user_buffer = 0, buffer_offset = 8280, buffer.resource = resource_10061]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10062], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10063], [is_user_buffer = 0, buffer_offset = 8040, buffer.resource = resource_10063]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10064], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)
pipe_context::set_vertex_buffers(pipe = context_2, num_buffers = 2, buffers = [[is_user_buffer = 0, buffer_offset = 0, buffer.resource = resource_10065], [is_user_buffer = 0, buffer_offset = 7608, buffer.resource = resource_10065]])
pipe_context::draw_vbo(pipe = context_2, info = [index_size = 2, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 0, max_index = 1257, primitive_restart = 0, restart_index = 0, index.resource = resource_10066], drawid_offset = 0, indirect = NULL, draws = [[start = 0, count = 1257, index_bias = 0]], num_draws = 1)

As expected, a huge chunk of the runtime is just set_vertex_buffers -> draw_vbo. Architecturally, this leads to a lot of unavoidably wasted cycles in drivers:

set_vertex_buffers “binds” vertex buffers to the context and flags state updates
draw_vbo checks all of the driver’s update-able states, updates the flagged ones, and then emits draws

But in the scenario where the driver can know ahead of time exactly what states will be updated, couldn’t that yield an improvement? For example, bundling these two calls into a single draw call would eliminate:

“binding” of vertex buffers
vbo state update flagging
draw-time validation
calling multiple driver entrypoints

In theory, it seems like this should be pretty good. And now that vertex buffer lifetimes have been reworked to use explicit ownership rather than garbage collection, it’s actually possible to do this. The optimal site for the optimization would be in threaded-context, where similar types of draw merging are already occurring.

The result looks something like this in a comparable trace:

pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1141, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 163536, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 191032, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771328, buffer.resource = resource_29602]], draws = [[start = 1141, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1146, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 218528, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 246144, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771360, buffer.resource = resource_29602]], draws = [[start = 1146, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1151, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 273760, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 301496, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771392, buffer.resource = resource_29602]], draws = [[start = 1151, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1156, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 329232, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 357088, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771424, buffer.resource = resource_29602]], draws = [[start = 1156, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1161, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 384944, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 412920, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771456, buffer.resource = resource_29602]], draws = [[start = 1161, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1166, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 440896, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 468992, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771488, buffer.resource = resource_29602]], draws = [[start = 1166, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1171, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 497088, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 525304, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771520, buffer.resource = resource_29602]], draws = [[start = 1171, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1176, max_index = 11, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 553520, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 582000, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771552, buffer.resource = resource_29602]], draws = [[start = 1176, count = 11]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1187, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 610480, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 639080, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771584, buffer.resource = resource_29602]], draws = [[start = 1187, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1192, max_index = 6, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 667680, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 696424, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771616, buffer.resource = resource_29602]], draws = [[start = 1192, count = 6]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1198, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 725168, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 754032, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771648, buffer.resource = resource_29602]], draws = [[start = 1198, count = 5]], num_draws = 1)
pipe_context::draw_vbo_buffers(pipe = pipe_2, info = [index_size = 0, has_user_indices = 0, mode = 5, start_instance = 0, instance_count = 1, min_index = 1203, max_index = 5, primitive_restart = 0, restart_index = 0, index.resource = NULL], buffer_count = 3, buffers = [[is_user_buffer = 0, buffer_offset = 782896, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 811880, buffer.resource = resource_30210], [is_user_buffer = 0, buffer_offset = 771680, buffer.resource = resource_29602]], draws = [[start = 1203, count = 5]], num_draws = 1)

It’s more compact, which is nice, but how does the perf look?

About another 40% improvement, now over 60fps: nearly double the endpoint of the last post. Huge.

And this is driving ecosystem improvements which will affect other apps and games which don’t even use zink.

Stay winning, Open Source graphics.

Written on September 16, 2025