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broadcom/compiler: let QPUs stall on TMU input/config overflows

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We have been trying to avoid this by tracking fifo usages in the driver and
flushing all outstanding TMU sequences if we overflowed any of these, however,
this is actually not the most efficient strategy. Instead, we would like to
flush only enough operations to get things going again, which is better for
pipelining. Doing that in the driver would require some additional work, but
thankfully, it is not required, since this seems to be what the hardware does
automatically, so we can just remove overflow tracking for these two fifos
and enjoy the benefits.

This also further improves shader-db stats:

total instructions in shared programs: 8975062 -> 8955145 (-0.22%)
instructions in affected programs: 1637624 -> 1617707 (-1.22%)
helped: 4050
HURT: 2241
Instructions are helped.

total threads in shared programs: 236802 -> 237042 (0.10%)
threads in affected programs: 252 -> 492 (95.24%)
helped: 122
HURT: 2
Threads are helped.

total sfu-stalls in shared programs: 19901 -> 19592 (-1.55%)
sfu-stalls in affected programs: 4744 -> 4435 (-6.51%)
helped: 1248
HURT: 1051
Sfu-stalls are helped.

total inst-and-stalls in shared programs: 8994963 -> 8974737 (-0.22%)
inst-and-stalls in affected programs: 1636184 -> 1615958 (-1.24%)
helped: 4050
HURT: 2239
Inst-and-stalls are helped.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8825>
This commit is contained in:
Iago Toral Quiroga
2021-02-03 09:14:00 +01:00
committed by Marge Bot
parent d57a358128
commit 6630825dcf
3 changed files with 50 additions and 43 deletions
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27
src/broadcom/compiler/v3d_compiler.h
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@@ -42,6 +42,25 @@
#include "qpu/qpu_instr.h"
#include "pipe/p_state.h"
/**
* Maximum number of outstanding TMU operations we can queue for execution.
*
* This is mostly limited by the size of the TMU fifos. The Input and Config
* fifos can stall, but we prefer that than injecting TMU flushes manually
* in the driver, so we can ignore these, but we can't overflow the Output fifo,
* which has 16 / threads per-thread entries, meaning that the maximum number
* of outstanding LDTMUs we can ever have is 8, for a 2-way threaded shader.
* This means that at most we can have 8 outstanding TMU loads, if each load
* is just one component.
*
* NOTE: we could actually have a larger value here because TMU stores don't
* consume any entries in the Output fifo (so we could have any number of
* outstanding stores) and the driver keeps track of used Output fifo entries
* and will flush if we ever needs more than 8, but since loads are much more
* common than stores, it is probably not worth it.
*/
#define MAX_TMU_QUEUE_SIZE 8
struct nir_builder;
struct v3d_fs_inputs {
@@ -573,15 +592,13 @@ struct v3d_compile {
*/
struct set *outstanding_regs;
uint32_t input_fifo_size;
uint32_t config_fifo_size;
uint32_t output_fifo_size;
struct {
nir_dest *dest;
uint8_t num_components;
uint8_t component_mask;
} flush[8]; /* 16 entries / 2 threads for input/output fifos */
} flush[MAX_TMU_QUEUE_SIZE];
uint32_t flush_count;
} tmu;
@@ -943,9 +960,9 @@ uint8_t vir_channels_written(struct qinst *inst);
struct qreg ntq_get_src(struct v3d_compile *c, nir_src src, int i);
void ntq_store_dest(struct v3d_compile *c, nir_dest *dest, int chan,
struct qreg result);
bool ntq_tmu_fifo_overflow(struct v3d_compile *c, uint32_t components, uint32_t writes);
bool ntq_tmu_fifo_overflow(struct v3d_compile *c, uint32_t components);
void ntq_add_pending_tmu_flush(struct v3d_compile *c, nir_dest *dest,
uint32_t component_mask, uint32_t tmu_writes);
uint32_t component_mask);
void ntq_flush_tmu(struct v3d_compile *c);
void vir_emit_thrsw(struct v3d_compile *c);