1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
|
llvm-exegesis - LLVM Machine Instruction Benchmark
==================================================
SYNOPSIS
--------
:program:`llvm-exegesis` [*options*]
DESCRIPTION
-----------
:program:`llvm-exegesis` is a benchmarking tool that uses information available
in LLVM to measure host machine instruction characteristics like latency or port
decomposition.
Given an LLVM opcode name and a benchmarking mode, :program:`llvm-exegesis`
generates a code snippet that makes execution as serial (resp. as parallel) as
possible so that we can measure the latency (resp. uop decomposition) of the
instruction.
The code snippet is jitted and executed on the host subtarget. The time taken
(resp. resource usage) is measured using hardware performance counters. The
result is printed out as YAML to the standard output.
The main goal of this tool is to automatically (in)validate the LLVM's TableDef
scheduling models. To that end, we also provide analysis of the results.
EXAMPLES: benchmarking
----------------------
Assume you have an X86-64 machine. To measure the latency of a single
instruction, run:
.. code-block:: bash
$ llvm-exegesis -mode=latency -opcode-name=ADD64rr
Measuring the uop decomposition of an instruction works similarly:
.. code-block:: bash
$ llvm-exegesis -mode=uops -opcode-name=ADD64rr
The output is a YAML document (the default is to write to stdout, but you can
redirect the output to a file using `-benchmarks-file`):
.. code-block:: none
---
key:
opcode_name: ADD64rr
mode: latency
config: ''
cpu_name: haswell
llvm_triple: x86_64-unknown-linux-gnu
num_repetitions: 10000
measurements:
- { key: latency, value: 1.0058, debug_string: '' }
error: ''
info: 'explicit self cycles, selecting one aliasing configuration.
Snippet:
ADD64rr R8, R8, R10
'
...
To measure the latency of all instructions for the host architecture, run:
.. code-block:: bash
#!/bin/bash
readonly INSTRUCTIONS=$(($(grep INSTRUCTION_LIST_END build/lib/Target/X86/X86GenInstrInfo.inc | cut -f2 -d=) - 1))
for INSTRUCTION in $(seq 1 ${INSTRUCTIONS});
do
./build/bin/llvm-exegesis -mode=latency -opcode-index=${INSTRUCTION} | sed -n '/---/,$p'
done
FIXME: Provide an :program:`llvm-exegesis` option to test all instructions.
EXAMPLES: analysis
----------------------
Assuming you have a set of benchmarked instructions (either latency or uops) as
YAML in file `/tmp/benchmarks.yaml`, you can analyze the results using the
following command:
.. code-block:: bash
$ llvm-exegesis -mode=analysis \
-benchmarks-file=/tmp/benchmarks.yaml \
-analysis-clusters-output-file=/tmp/clusters.csv \
-analysis-inconsistencies-output-file=/tmp/inconsistencies.txt
This will group the instructions into clusters with the same performance
characteristics. The clusters will be written out to `/tmp/clusters.csv` in the
following format:
.. code-block:: none
cluster_id,opcode_name,config,sched_class
...
2,ADD32ri8_DB,,WriteALU,1.00
2,ADD32ri_DB,,WriteALU,1.01
2,ADD32rr,,WriteALU,1.01
2,ADD32rr_DB,,WriteALU,1.00
2,ADD32rr_REV,,WriteALU,1.00
2,ADD64i32,,WriteALU,1.01
2,ADD64ri32,,WriteALU,1.01
2,MOVSX64rr32,,BSWAP32r_BSWAP64r_MOVSX64rr32,1.00
2,VPADDQYrr,,VPADDBYrr_VPADDDYrr_VPADDQYrr_VPADDWYrr_VPSUBBYrr_VPSUBDYrr_VPSUBQYrr_VPSUBWYrr,1.02
2,VPSUBQYrr,,VPADDBYrr_VPADDDYrr_VPADDQYrr_VPADDWYrr_VPSUBBYrr_VPSUBDYrr_VPSUBQYrr_VPSUBWYrr,1.01
2,ADD64ri8,,WriteALU,1.00
2,SETBr,,WriteSETCC,1.01
...
:program:`llvm-exegesis` will also analyze the clusters to point out
inconsistencies in the scheduling information. The output is an html file. For
example, `/tmp/inconsistencies.html` will contain messages like the following :
.. image:: llvm-exegesis-analysis.png
:align: center
Note that the scheduling class names will be resolved only when
:program:`llvm-exegesis` is compiled in debug mode, else only the class id will
be shown. This does not invalidate any of the analysis results though.
OPTIONS
-------
.. option:: -help
Print a summary of command line options.
.. option:: -opcode-index=<LLVM opcode index>
Specify the opcode to measure, by index.
Either `opcode-index` or `opcode-name` must be set.
.. option:: -opcode-name=<LLVM opcode name>
Specify the opcode to measure, by name.
Either `opcode-index` or `opcode-name` must be set.
.. option:: -mode=[latency|uops|analysis]
Specify the run mode.
.. option:: -num-repetitions=<Number of repetition>
Specify the number of repetitions of the asm snippet.
Higher values lead to more accurate measurements but lengthen the benchmark.
.. option:: -benchmarks-file=</path/to/file>
File to read (`analysis` mode) or write (`latency`/`uops` modes) benchmark
results. "-" uses stdin/stdout.
.. option:: -analysis-clusters-output-file=</path/to/file>
If provided, write the analysis clusters as CSV to this file. "-" prints to
stdout.
.. option:: -analysis-inconsistencies-output-file=</path/to/file>
If non-empty, write inconsistencies found during analysis to this file. `-`
prints to stdout.
.. option:: -analysis-numpoints=<dbscan numPoints parameter>
Specify the numPoints parameters to be used for DBSCAN clustering
(`analysis` mode).
.. option:: -analysis-espilon=<dbscan epsilon parameter>
Specify the numPoints parameters to be used for DBSCAN clustering
(`analysis` mode).
.. option:: -ignore-invalid-sched-class=false
If set, ignore instructions that do not have a sched class (class idx = 0).
EXIT STATUS
-----------
:program:`llvm-exegesis` returns 0 on success. Otherwise, an error message is
printed to standard error, and the tool returns a non 0 value.
|
