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broadcom/compiler: don't over-estimate latency of TMU instructions

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Over-estimating latency can cause us to delay the critical paths of
the shader unnecessarily, producing larger QPU programs that take more
time to execute as a result (and it also adds register pressure) so
striking a balance is important. The thread switching model in V3D
is quite effective at hiding latency and usuallly we just need to
hint it to delay TMU instructions a little bit to find the best
compromise for performance.

The new latency numbers have been chosen empirically by testing
V3DV with Sponza and a few UE4 samples.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17451>
This commit is contained in:
Iago Toral Quiroga 2022-07-08 13:37:02 +02:00 • committed by Marge Bot
parent f227aa7c98
commit 871a7536e8
1 changed files with 10 additions and 3 deletions
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13
src/broadcom/compiler/vir.c
View file

@ -1146,6 +1146,13 @@ v3d_instr_delay_cb(nir_instr *instr, void *data)
case nir_instr_type_phi:
return 1;
/* We should not use very large delays for TMU instructions. Typically,
* thread switches will be sufficient to hide all or most of the latency,
* so we typically only need a little bit of extra room. If we over-estimate
* the latency here we may end up unnecesarily delaying the critical path in
* the shader, which would have a negative effect in performance, so here
* we are trying to strike a balance based on empirical testing.
*/
case nir_instr_type_intrinsic: {
if (!c->disable_general_tmu_sched) {
nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
@ -1154,10 +1161,10 @@ v3d_instr_delay_cb(nir_instr *instr, void *data)
case nir_intrinsic_load_scratch:
case nir_intrinsic_load_shared:
case nir_intrinsic_image_load:
return 30;
return 3;
case nir_intrinsic_load_ubo:
if (nir_src_is_divergent(intr->src[1]))
return 30;
return 3;
FALLTHROUGH;
default:
return 1;
@ -1169,7 +1176,7 @@ v3d_instr_delay_cb(nir_instr *instr, void *data)
}
case nir_instr_type_tex:
return 50;
return 5;
}
return 0;