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nak: allow a bit of spilling when we hit 8 warps per sm

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If we risk a bit of spilling we can run +50% threads concurrently that
should work in our favor most of the time.

Increases performance in pixmark_piano by 15%.

Totals from 761 (0.06% of 1212873) affected shaders:
CodeSize: 53351440 -> 54550752 (+2.25%); split: -0.00%, +2.25%
Number of GPRs: 137160 -> 126408 (-7.84%)
SLM Size: 12052 -> 47456 (+293.76%)
Static cycle count: 85992784 -> 88649262 (+3.09%); split: -0.00%, +3.09%
Spills to memory: 0 -> 31656 (+inf%)
Fills from memory: 0 -> 31656 (+inf%)
Max warps/SM: 6088 -> 9132 (+50.00%)
This commit is contained in:
Karol Herbst 2026-04-11 00:40:29 +02:00 • committed by Karol Herbst
parent c7ab501171
commit 88fbcee585
1 changed files with 22 additions and 0 deletions
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22
src/nouveau/compiler/nak/assign_regs.rs
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@ -1486,6 +1486,28 @@ impl Shader<'_> {
);
}
// We try to check if allocating a few fewer registers would allow us
// to run 12 instead of 8 warps concurrently.
// The assumption is that running +50% threads will give us more
// performance than we lose with a bit of spilling.
let actual_gprs = (total_gprs + hw_reserved_gprs).min(max_gprs);
let warps_per_sm = max_warps_per_sm(self.sm, actual_gprs);
if warps_per_sm == 8 {
let new_max = if max_warps_per_sm(self.sm, actual_gprs - 8) > 8 {
total_gprs - 8
} else if max_warps_per_sm(self.sm, actual_gprs - 16) > 8 {
// This gives us +15% performance in pixmark_piano
total_gprs - 16
} else {
0
};
if new_max != 0 {
max_gprs = (new_max.next_multiple_of(8) - hw_reserved_gprs)
.min(max_gprs);
}
}
if total_gprs > max_gprs {
// If we're spilling GPRs, we need to reserve 2 GPRs for OpParCopy
// lowering because it needs to be able lower Mem copies which