OV - attention-clang-znver5-256 - Loop 49 - attention-clang-znver5-256

	Loop Id: 49	Module: attention-clang-znver5-256	Source: attention_v2.cpp:55-56	Coverage: 1.14%

0x67ea VMOVUPS	(%R14,%R13,4),%YMM0    [2]

0x67f0 VSUBPS	0x3e0(%RSP),%YMM0,%YMM0    [1]

0x67f9 VMOVAPS	%YMM0,0x140(%RSP)    [1]

0x6802 VEXTRACTF128	$0x1,%YMM0,%XMM0

0x6808 VMOVAPS	%XMM0,0xa0(%RSP)    [1]

0x6811 VZEROUPPER

0x6814 CALL	1160 <expf@plt>

0x6819 VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x6822 VMOVSHDUP	0xa0(%RSP),%XMM0    [1]

0x682b CALL	1160 <expf@plt>

0x6830 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x6839 VINSERTPS	$0x10,%XMM0,%XMM1,%XMM0

0x683f VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x6848 VPERMILPD	$0x1,0xa0(%RSP),%XMM0    [1]

0x6853 CALL	1160 <expf@plt>

0x6858 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x6861 VINSERTPS	$0x20,%XMM0,%XMM1,%XMM0

0x6867 VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x6870 VPERMILPS	$-0x1,0xa0(%RSP),%XMM0    [1]

0x687b CALL	1160 <expf@plt>

0x6880 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x6889 VINSERTPS	$0x30,%XMM0,%XMM1,%XMM0

0x688f VMOVAPS	%XMM0,0xa0(%RSP)    [1]

0x6898 VMOVAPS	0x140(%RSP),%YMM0    [1]

0x68a1 VZEROUPPER

0x68a4 CALL	1160 <expf@plt>

0x68a9 VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x68b2 VMOVSHDUP	0x140(%RSP),%XMM0    [1]

0x68bb CALL	1160 <expf@plt>

0x68c0 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x68c9 VINSERTPS	$0x10,%XMM0,%XMM1,%XMM0

0x68cf VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x68d8 VPERMILPD	$0x1,0x140(%RSP),%XMM0    [1]

0x68e3 CALL	1160 <expf@plt>

0x68e8 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x68f1 VINSERTPS	$0x20,%XMM0,%XMM1,%XMM0

0x68f7 VMOVAPS	%XMM0,0xe0(%RSP)    [1]

0x6900 VPERMILPS	$-0x1,0x140(%RSP),%XMM0    [1]

0x690b CALL	1160 <expf@plt>

0x6910 VMOVAPS	0xe0(%RSP),%XMM1    [1]

0x6919 VINSERTPS	$0x30,%XMM0,%XMM1,%XMM0

0x691f VINSERTF128	$0x1,0xa0(%RSP),%YMM0,%YMM0    [1]

0x692a VDIVPS	0x320(%RSP),%YMM0,%YMM0    [1]

0x6933 VMOVUPS	%YMM0,(%R15,%R13,4)    [3]

0x6939 ADD	$0x8,%R13

0x693d CMP	%R13,0x70(%RSP)    [1]

0x6942 JNE	67ea

/home/eoseret/llm-attention/attention_v2.cpp: 55 - 56

--------------------------------------------------------------------------------

55:       for (int idx = 0; idx <= row; ++idx)  //vectorised

56:          P[row * N + idx] = expf(S_row[idx] - max_val) / sum;

Coverage (%)	Name	Source Location	Module

min	med	avg	max

Percentile Index	10	20	30	40	50	60	70	80	90	100
Value

min	med	avg	max

Percentile Index	10	20	30	40	50	60	70	80	90	100
Value

Path /

Metric	Value
CQA speedup if no scalar integer	1.00
CQA speedup if FP arith vectorized	1.02
CQA speedup if fully vectorized	3.47
CQA speedup if no inter-iteration dependency	NA
CQA speedup if next bottleneck killed	1.04
Bottlenecks	P6, P7, P8, P9,
Function	main
Source	attention_v2.cpp:55-56
Source loop unroll info	unrolled by 8
Source loop unroll confidence level	max
Unroll/vectorization loop type	main
Unroll factor	8
CQA cycles	7.00
CQA cycles if no scalar integer	7.00
CQA cycles if FP arith vectorized	6.88
CQA cycles if fully vectorized	2.02
Front-end cycles	6.75
P0 cycles	0.33
P1 cycles	0.33
P2 cycles	0.33
P3 cycles	0.33
P4 cycles	0.33
P5 cycles	0.33
P6 cycles	7.00
P7 cycles	7.00
P8 cycles	7.00
P9 cycles	7.00
P10 cycles	3.50
P11 cycles	3.50
P12 cycles	3.50
P13 cycles	3.50
P14 cycles	5.00
P15 cycles	5.00
DIV/SQRT cycles	2.50
Inter-iter dependencies cycles	1
FE+BE cycles (UFS)	NA
Stall cycles (UFS)	NA
Nb insns	47.00
Nb uops	54.00
Nb loads	18.00
Nb stores	10.00
Nb stack references	6.00
FLOP/cycle	2.29
Nb FLOP add-sub	8.00
Nb FLOP mul	0.00
Nb FLOP fma	0.00
Nb FLOP div	8.00
Nb FLOP rcp	0.00
Nb FLOP sqrt	0.00
Nb FLOP rsqrt	0.00
Bytes/cycle	76.57
Bytes prefetched	0.00
Bytes loaded	344.00
Bytes stored	192.00
Stride 0	1.00
Stride 1	2.00
Stride n	0.00
Stride unknown	0.00
Stride indirect	0.00
Vectorization ratio all	83.33
Vectorization ratio load	100.00
Vectorization ratio store	100.00
Vectorization ratio mul	NA
Vectorization ratio add_sub	100.00
Vectorization ratio fma	NA
Vectorization ratio div_sqrt	100.00
Vectorization ratio other	57.14
Vector-efficiency ratio all	25.35
Vector-efficiency ratio load	29.41
Vector-efficiency ratio store	30.00
Vector-efficiency ratio mul	NA
Vector-efficiency ratio add_sub	50.00
Vector-efficiency ratio fma	NA
Vector-efficiency ratio div_sqrt	50.00
Vector-efficiency ratio other	16.96

Metric	Value
CQA speedup if no scalar integer	1.00
CQA speedup if FP arith vectorized	1.02
CQA speedup if fully vectorized	3.47
CQA speedup if no inter-iteration dependency	NA
CQA speedup if next bottleneck killed	1.04
Bottlenecks	P6, P7, P8, P9,
Function	main
Source	attention_v2.cpp:55-56
Source loop unroll info	unrolled by 8
Source loop unroll confidence level	max
Unroll/vectorization loop type	main
Unroll factor	8
CQA cycles	7.00
CQA cycles if no scalar integer	7.00
CQA cycles if FP arith vectorized	6.88
CQA cycles if fully vectorized	2.02
Front-end cycles	6.75
P0 cycles	0.33
P1 cycles	0.33
P2 cycles	0.33
P3 cycles	0.33
P4 cycles	0.33
P5 cycles	0.33
P6 cycles	7.00
P7 cycles	7.00
P8 cycles	7.00
P9 cycles	7.00
P10 cycles	3.50
P11 cycles	3.50
P12 cycles	3.50
P13 cycles	3.50
P14 cycles	5.00
P15 cycles	5.00
DIV/SQRT cycles	2.50
Inter-iter dependencies cycles	1
FE+BE cycles (UFS)	NA
Stall cycles (UFS)	NA
Nb insns	47.00
Nb uops	54.00
Nb loads	18.00
Nb stores	10.00
Nb stack references	6.00
FLOP/cycle	2.29
Nb FLOP add-sub	8.00
Nb FLOP mul	0.00
Nb FLOP fma	0.00
Nb FLOP div	8.00
Nb FLOP rcp	0.00
Nb FLOP sqrt	0.00
Nb FLOP rsqrt	0.00
Bytes/cycle	76.57
Bytes prefetched	0.00
Bytes loaded	344.00
Bytes stored	192.00
Stride 0	1.00
Stride 1	2.00
Stride n	0.00
Stride unknown	0.00
Stride indirect	0.00
Vectorization ratio all	83.33
Vectorization ratio load	100.00
Vectorization ratio store	100.00
Vectorization ratio mul	NA
Vectorization ratio add_sub	100.00
Vectorization ratio fma	NA
Vectorization ratio div_sqrt	100.00
Vectorization ratio other	57.14
Vector-efficiency ratio all	25.35
Vector-efficiency ratio load	29.41
Vector-efficiency ratio store	30.00
Vector-efficiency ratio mul	NA
Vector-efficiency ratio add_sub	50.00
Vector-efficiency ratio fma	NA
Vector-efficiency ratio div_sqrt	50.00
Vector-efficiency ratio other	16.96

Path /

Average path: Display a virtual path defined by average values of all real paths

Function	main
Source file and lines	attention_v2.cpp:55-56
Module	attention-clang-znver5-256

The loop is defined in /home/eoseret/llm-attention/attention_v2.cpp:55-56.

It is main loop of related source loop which is unrolled by 8 (including vectorization).

gain
potential
hint
expert

Vectorization

Your loop is partially vectorized. Only 25% of vector register length is used (average across all SSE/AVX instructions).

Details

83% of SSE/AVX instructions are used in vector version (process two or more data elements in vector registers):

57% of SSE/AVX instructions that are not load, store, addition, subtraction nor multiply instructions are used in vector version.

Workaround

Read the "512-bits vectorization" report at "Potential" confidence level.

Execution units bottlenecks

Performance is limited by:

reading data from caches/RAM (load units are a bottleneck)
writing data to caches/RAM (the store unit is a bottleneck)

Workaround

Read less array elements
Write less array elements
Provide more information to your compiler:
- hardcode the bounds of the corresponding 'for' loop

512-bits vectorization

On some x86 processors supporting 512-bits vectorization, compilers are often too conservative and limit vectorization to 256 bits. Performance can then be improved by enforcing 512-bits vectorization, especially with many vectorized and high trip count loops. 512-bits vectorization performance overhead (compared to 256-bits) is generally lower on newer processors.

Workaround

Recompile with -mprefer-vector-width=512

CALL instructions

Detected function call instructions.

Details

Calling (and then returning from) a function prevents many compiler optimizations (like vectorization), breaks control flow (which reduces pipeline performance) and executes extra instructions to save/restore the registers used inside it, which is very expensive (dozens of cycles). Consider to inline small functions.

expf@plt: 8 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56

Vector unaligned load/store instructions

Detected 2 suboptimal vector unaligned load/store instructions.

Details

VEXTRACTF128: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56
VINSERTF128: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56

Workaround

Pass to your compiler a micro-architecture specialization option:
- use march=native
Use vector aligned instructions:
1. align your arrays on 64 bytes boundaries: replace { void *p = malloc (size); } with { void *p; posix_memalign (&p, 64, size); }.
2. inform your compiler that your arrays are vector aligned: if array 'foo' is 64 bytes-aligned, define a pointer 'p_foo' as __builtin_assume_aligned (foo, 64) and use it instead of 'foo' in the loop.

Type of elements and instruction set

2 AVX instructions are processing arithmetic or math operations on single precision FP elements in vector mode (eight at a time).

Matching between your loop (in the source code) and the binary loop

The binary loop is composed of 16 FP arithmetical operations:

8: addition or subtraction
8: divide

The binary loop is loading 344 bytes (86 single precision FP elements). The binary loop is storing 192 bytes (48 single precision FP elements).

Arithmetic intensity

Arithmetic intensity is 0.03 FP operations per loaded or stored byte.

General properties

nb instructions	47
nb uops	54
loop length	350
used x86 registers	4
used mmx registers	0
used xmm registers	2
used ymm registers	1
used zmm registers	0
nb stack references	6

Front-end

ASSUMED MACRO FUSION FIT IN UOP CACHE

micro-operation queue	6.75 cycles
front end	6.75 cycles

Back-end

	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	P12	P13	P14	P15
uops	0.33	0.33	0.33	0.33	0.33	0.33	7.00	7.00	7.00	7.00	3.50	3.50	3.50	3.50	5.00	5.00
cycles	0.33	0.33	0.33	0.33	0.33	0.33	7.00	7.00	7.00	7.00	3.50	3.50	3.50	3.50	5.00	5.00

Execution ports to units layout:

P0: ALU
P1: ALU
P2: ALU
P3: ALU, BRU
P4: ALU, BRU
P5: ALU, BRU
P6 (512 bits): store address, load
P7 (512 bits): store address, load
P8 (512 bits): store address, load
P9 (512 bits): store address, load
P10 (512 bits): VPU, DIV/SQRT
P11 (512 bits): VPU, DIV/SQRT
P12 (512 bits): VPU
P13 (512 bits): VPU
P14 (512 bits): FP store data
P15 (512 bits): FP store data

Cycles executing div or sqrt instructions	2.50
Longest recurrence chain latency (RecMII)	1.00

Cycles summary

Front-end	6.75
Dispatch	7.00
DIV/SQRT	2.50
Data deps.	1.00
Overall L1	7.00

Vectorization ratios

INT

all	100%
load	NA (no load vectorizable/vectorized instructions)
store	NA (no store vectorizable/vectorized instructions)
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
other	100%

all	82%
load	100%
store	100%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	100%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	100%
other	50%

INT+FP

all	83%
load	100%
store	100%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	100%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	100%
other	57%

Vector efficiency ratios

INT

all	25%
load	NA (no load vectorizable/vectorized instructions)
store	NA (no store vectorizable/vectorized instructions)
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
other	25%

all	25%
load	29%
store	30%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	50%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	50%
other	15%

INT+FP

all	25%
load	29%
store	30%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	50%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	50%
other	16%

Cycles and memory resources usage

Assuming all data fit into the L1 cache, each iteration of the binary loop takes 7.00 cycles. At this rate:

19% of peak load performance is reached (49.14 out of 256.00 bytes loaded per cycle (GB/s @ 1GHz))
21% of peak store performance is reached (27.43 out of 128.00 bytes stored per cycle (GB/s @ 1GHz))

Front-end bottlenecks

Found no such bottlenecks.

ASM code

In the binary file, the address of the loop is: 67ea

Instruction	Nb FU	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	P12	P13	P14	P15	Latency	Recip. throughput	Vectorization
VMOVUPS (%R14,%R13,4),%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (50.0%)
VSUBPS 0x3e0(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0.50	0.50	0	0	2	0.50	vect (50.0%)
VMOVAPS %YMM0,0x140(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (50.0%)
VEXTRACTF128 $0x1,%YMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	vect (25.0%)
VMOVAPS %XMM0,0xa0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VZEROUPPER	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVSHDUP 0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.50	vect (12.5%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x10,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPD $0x1,0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x20,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPS $-0x1,0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x30,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xa0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVAPS 0x140(%RSP),%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (50.0%)
VZEROUPPER	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVSHDUP 0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.50	vect (12.5%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x10,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPD $0x1,0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x20,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPS $-0x1,0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x30,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VINSERTF128 $0x1,0xa0(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0.50	0.50	0	0	0	2	0.50	vect (25.0%)
VDIVPS 0x320(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.50	0.50	0	0	0	0	10	2.50	vect (50.0%)
VMOVUPS %YMM0,(%R15,%R13,4)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (50.0%)
ADD $0x8,%R13	1	0.17	0.17	0.17	0.17	0.17	0.17	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
CMP %R13,0x70(%RSP)	1	0.17	0.17	0.17	0.17	0.17	0.17	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.25	N/A
JNE 67ea <main+0x3a1a>	1	0	0	0	0.33	0.33	0.33	0	0	0	0	0	0	0	0	0	0	0	0.33-0.50	N/A

Function	main
Source file and lines	attention_v2.cpp:55-56
Module	attention-clang-znver5-256

The loop is defined in /home/eoseret/llm-attention/attention_v2.cpp:55-56.

It is main loop of related source loop which is unrolled by 8 (including vectorization).

gain
potential
hint
expert

Vectorization

Your loop is partially vectorized. Only 25% of vector register length is used (average across all SSE/AVX instructions).

Details

83% of SSE/AVX instructions are used in vector version (process two or more data elements in vector registers):

57% of SSE/AVX instructions that are not load, store, addition, subtraction nor multiply instructions are used in vector version.

Workaround

Read the "512-bits vectorization" report at "Potential" confidence level.

Execution units bottlenecks

Performance is limited by:

reading data from caches/RAM (load units are a bottleneck)
writing data to caches/RAM (the store unit is a bottleneck)

Workaround

Read less array elements
Write less array elements
Provide more information to your compiler:
- hardcode the bounds of the corresponding 'for' loop

512-bits vectorization

Workaround

Recompile with -mprefer-vector-width=512

CALL instructions

Detected function call instructions.

Details

expf@plt: 8 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56
- /home/eoseret/llm-attention/attention_v2.cpp:56

Vector unaligned load/store instructions

Detected 2 suboptimal vector unaligned load/store instructions.

Details

VEXTRACTF128: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56
VINSERTF128: 1 occurrences►
- /home/eoseret/llm-attention/attention_v2.cpp:56

Workaround

Pass to your compiler a micro-architecture specialization option:
- use march=native
Use vector aligned instructions:
1. align your arrays on 64 bytes boundaries: replace { void *p = malloc (size); } with { void *p; posix_memalign (&p, 64, size); }.
2. inform your compiler that your arrays are vector aligned: if array 'foo' is 64 bytes-aligned, define a pointer 'p_foo' as __builtin_assume_aligned (foo, 64) and use it instead of 'foo' in the loop.

Type of elements and instruction set

2 AVX instructions are processing arithmetic or math operations on single precision FP elements in vector mode (eight at a time).

Matching between your loop (in the source code) and the binary loop

The binary loop is composed of 16 FP arithmetical operations:

8: addition or subtraction
8: divide

The binary loop is loading 344 bytes (86 single precision FP elements). The binary loop is storing 192 bytes (48 single precision FP elements).

Arithmetic intensity

Arithmetic intensity is 0.03 FP operations per loaded or stored byte.

General properties

nb instructions	47
nb uops	54
loop length	350
used x86 registers	4
used mmx registers	0
used xmm registers	2
used ymm registers	1
used zmm registers	0
nb stack references	6

Front-end

ASSUMED MACRO FUSION FIT IN UOP CACHE

micro-operation queue	6.75 cycles
front end	6.75 cycles

Back-end

	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	P12	P13	P14	P15
uops	0.33	0.33	0.33	0.33	0.33	0.33	7.00	7.00	7.00	7.00	3.50	3.50	3.50	3.50	5.00	5.00
cycles	0.33	0.33	0.33	0.33	0.33	0.33	7.00	7.00	7.00	7.00	3.50	3.50	3.50	3.50	5.00	5.00

Execution ports to units layout:

P0: ALU
P1: ALU
P2: ALU
P3: ALU, BRU
P4: ALU, BRU
P5: ALU, BRU
P6 (512 bits): store address, load
P7 (512 bits): store address, load
P8 (512 bits): store address, load
P9 (512 bits): store address, load
P10 (512 bits): VPU, DIV/SQRT
P11 (512 bits): VPU, DIV/SQRT
P12 (512 bits): VPU
P13 (512 bits): VPU
P14 (512 bits): FP store data
P15 (512 bits): FP store data

Cycles executing div or sqrt instructions	2.50
Longest recurrence chain latency (RecMII)	1.00

Cycles summary

Front-end	6.75
Dispatch	7.00
DIV/SQRT	2.50
Data deps.	1.00
Overall L1	7.00

Vectorization ratios

INT

all	100%
load	NA (no load vectorizable/vectorized instructions)
store	NA (no store vectorizable/vectorized instructions)
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
other	100%

all	82%
load	100%
store	100%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	100%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	100%
other	50%

INT+FP

all	83%
load	100%
store	100%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	100%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	100%
other	57%

Vector efficiency ratios

INT

all	25%
load	NA (no load vectorizable/vectorized instructions)
store	NA (no store vectorizable/vectorized instructions)
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	NA (no add-sub vectorizable/vectorized instructions)
fma	NA (no fma vectorizable/vectorized instructions)
other	25%

all	25%
load	29%
store	30%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	50%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	50%
other	15%

INT+FP

all	25%
load	29%
store	30%
mul	NA (no mul vectorizable/vectorized instructions)
add-sub	50%
fma	NA (no fma vectorizable/vectorized instructions)
div/sqrt	50%
other	16%

Cycles and memory resources usage

Assuming all data fit into the L1 cache, each iteration of the binary loop takes 7.00 cycles. At this rate:

19% of peak load performance is reached (49.14 out of 256.00 bytes loaded per cycle (GB/s @ 1GHz))
21% of peak store performance is reached (27.43 out of 128.00 bytes stored per cycle (GB/s @ 1GHz))

Front-end bottlenecks

Found no such bottlenecks.

ASM code

In the binary file, the address of the loop is: 67ea

Instruction	Nb FU	P0	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10	P11	P12	P13	P14	P15	Latency	Recip. throughput	Vectorization
VMOVUPS (%R14,%R13,4),%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (50.0%)
VSUBPS 0x3e0(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0.50	0.50	0	0	2	0.50	vect (50.0%)
VMOVAPS %YMM0,0x140(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (50.0%)
VEXTRACTF128 $0x1,%YMM0,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	vect (25.0%)
VMOVAPS %XMM0,0xa0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VZEROUPPER	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVSHDUP 0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.50	vect (12.5%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x10,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPD $0x1,0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x20,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPS $-0x1,0xa0(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x30,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xa0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVAPS 0x140(%RSP),%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (50.0%)
VZEROUPPER	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VMOVSHDUP 0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.50	vect (12.5%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x10,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPD $0x1,0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x20,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VMOVAPS %XMM0,0xe0(%RSP)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (25.0%)
VPERMILPS $-0x1,0x140(%RSP),%XMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0	0	1-2	0.50	vect (25.0%)
CALL 1160 <expf@plt>	2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	N/A
VMOVAPS 0xe0(%RSP),%XMM1	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0	0	3	0.50	vect (25.0%)
VINSERTPS $0x30,%XMM0,%XMM1,%XMM0	1	0	0	0	0	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	2	0.25	scal (6.3%)
VINSERTF128 $0x1,0xa0(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0.50	0.50	0	0	0	2	0.50	vect (25.0%)
VDIVPS 0x320(%RSP),%YMM0,%YMM0	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0.50	0.50	0	0	0	0	10	2.50	vect (50.0%)
VMOVUPS %YMM0,(%R15,%R13,4)	1	0	0	0	0	0	0	0.25	0.25	0.25	0.25	0	0	0	0	0.50	0.50	4	0.50	vect (50.0%)
ADD $0x8,%R13	1	0.17	0.17	0.17	0.17	0.17	0.17	0	0	0	0	0	0	0	0	0	0	1	0.17	N/A
CMP %R13,0x70(%RSP)	1	0.17	0.17	0.17	0.17	0.17	0.17	0.25	0.25	0.25	0.25	0	0	0	0	0	0	1	0.25	N/A
JNE 67ea <main+0x3a1a>	1	0	0	0	0.33	0.33	0.33	0	0	0	0	0	0	0	0	0	0	0	0.33-0.50	N/A

Report Configuration

Vectorization

Details

Workaround

Execution units bottlenecks

Workaround

512-bits vectorization

Workaround

CALL instructions

Details

Vector unaligned load/store instructions

Details

Workaround

Type of elements and instruction set

Matching between your loop (in the source code) and the binary loop

Arithmetic intensity

General properties

Front-end

Back-end

Cycles summary

Vectorization ratios

Vector efficiency ratios

Cycles and memory resources usage

Front-end bottlenecks

ASM code

Vectorization

Details

Workaround

Execution units bottlenecks

Workaround

512-bits vectorization

Workaround

CALL instructions

Details

Vector unaligned load/store instructions

Details

Workaround

Type of elements and instruction set

Matching between your loop (in the source code) and the binary loop

Arithmetic intensity

General properties

Front-end

Back-end

Cycles summary

Vectorization ratios

Vector efficiency ratios

Cycles and memory resources usage

Front-end bottlenecks

ASM code