[llvm-exegesis] Opcode stabilization / reclusterization (PR40715)
Summary:
Given an instruction `Opcode`, we can make benchmarks (measurements) of the
instruction characteristics/performance. Then, to facilitate further analysis
we group the benchmarks with *similar* characteristics into clusters.
Now, this is all not entirely deterministic. Some instructions have variable
characteristics, depending on their arguments. And thus, if we do several
benchmarks of the same instruction `Opcode`, we may end up with *different*
performance characteristics measurements. And when we then do clustering,
these several benchmarks of the same instruction `Opcode` may end up being
clustered into *different* clusters. This is not great for further analysis.
We shall find every `Opcode` with benchmarks not in just one cluster, and move
*all* the benchmarks of said `Opcode` into one new unstable cluster per `Opcode`.
I have solved this by making `ClusterId` a bit field, adding a `IsUnstable` bit,
and introducing `-analysis-display-unstable-clusters` switch to toggle between
displaying stable-only clusters and unstable-only clusters.
The reclusterization is deterministically stable, produces identical reports
between runs. (Or at least that is what i'm seeing, maybe it isn't)
Timings/comparisons:
old (current trunk/head) {
F8303582}
```
$ perf stat -r 25 ./bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-old.html
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-old.html'
...
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-old.html'
Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-old.html' (25 runs):
6624.73 msec task-clock # 0.999 CPUs utilized ( +- 0.53% )
172 context-switches # 25.965 M/sec ( +- 29.89% )
0 cpu-migrations # 0.042 M/sec ( +- 56.54% )
31073 page-faults # 4690.754 M/sec ( +- 0.08% )
26538711696 cycles #
4006230.292 GHz ( +- 0.53% ) (83.31%)
2017496807 stalled-cycles-frontend # 7.60% frontend cycles idle ( +- 0.93% ) (83.32%)
13403650062 stalled-cycles-backend # 50.51% backend cycles idle ( +- 0.33% ) (33.37%)
19770706799 instructions # 0.74 insn per cycle
# 0.68 stalled cycles per insn ( +- 0.04% ) (50.04%)
4419821812 branches #
667207369.714 M/sec ( +- 0.03% ) (66.69%)
121741669 branch-misses # 2.75% of all branches ( +- 0.28% ) (83.34%)
6.6283 +- 0.0358 seconds time elapsed ( +- 0.54% )
```
patch, with reclustering but without filtering (i.e. outputting all the stable *and* unstable clusters) {
F8303586}
```
$ perf stat -r 25 ./bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-all.html
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-all.html'
...
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-all.html'
Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-all.html' (25 runs):
6475.29 msec task-clock # 0.999 CPUs utilized ( +- 0.31% )
213 context-switches # 32.952 M/sec ( +- 23.81% )
1 cpu-migrations # 0.130 M/sec ( +- 43.84% )
31287 page-faults # 4832.057 M/sec ( +- 0.08% )
25939086577 cycles #
4006160.279 GHz ( +- 0.31% ) (83.31%)
1958812858 stalled-cycles-frontend # 7.55% frontend cycles idle ( +- 0.68% ) (83.32%)
13218961512 stalled-cycles-backend # 50.96% backend cycles idle ( +- 0.29% ) (33.37%)
19752995402 instructions # 0.76 insn per cycle
# 0.67 stalled cycles per insn ( +- 0.04% ) (50.04%)
4417079244 branches #
682195472.305 M/sec ( +- 0.03% ) (66.70%)
121510065 branch-misses # 2.75% of all branches ( +- 0.19% ) (83.34%)
6.4832 +- 0.0229 seconds time elapsed ( +- 0.35% )
```
Funnily, *this* measurement shows that said reclustering actually improved performance.
patch, with reclustering, only the stable clusters {
F8303594}
```
$ perf stat -r 25 ./bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-stable.html
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-stable.html'
...
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-stable.html'
Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-stable.html' (25 runs):
6387.71 msec task-clock # 0.999 CPUs utilized ( +- 0.13% )
133 context-switches # 20.792 M/sec ( +- 23.39% )
0 cpu-migrations # 0.063 M/sec ( +- 61.24% )
31318 page-faults # 4903.256 M/sec ( +- 0.08% )
25591984967 cycles #
4006786.266 GHz ( +- 0.13% ) (83.31%)
1881234904 stalled-cycles-frontend # 7.35% frontend cycles idle ( +- 0.25% ) (83.33%)
13209749965 stalled-cycles-backend # 51.62% backend cycles idle ( +- 0.16% ) (33.36%)
19767554347 instructions # 0.77 insn per cycle
# 0.67 stalled cycles per insn ( +- 0.04% ) (50.03%)
4417480305 branches #
691618858.046 M/sec ( +- 0.03% ) (66.68%)
118676358 branch-misses # 2.69% of all branches ( +- 0.07% ) (83.33%)
6.3954 +- 0.0118 seconds time elapsed ( +- 0.18% )
```
Performance improved even further?! Makes sense i guess, less clusters to print.
patch, with reclustering, only the unstable clusters {
F8303601}
```
$ perf stat -r 25 ./bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-unstable.html -analysis-display-unstable-clusters
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-unstable.html'
...
no exegesis target for x86_64-unknown-linux-gnu, using default
Parsed 43970 benchmark points
Printing sched class consistency analysis results to file '/tmp/clusters-new-unstable.html'
Performance counter stats for './bin/llvm-exegesis -mode=analysis -analysis-epsilon=0.5 -benchmarks-file=/home/lebedevri/PileDriver-Sched/benchmarks-inverse_throughput.yaml -analysis-inconsistencies-output-file=/tmp/clusters-new-unstable.html -analysis-display-unstable-clusters' (25 runs):
6124.96 msec task-clock # 1.000 CPUs utilized ( +- 0.20% )
194 context-switches # 31.709 M/sec ( +- 20.46% )
0 cpu-migrations # 0.039 M/sec ( +- 49.77% )
31413 page-faults # 5129.261 M/sec ( +- 0.06% )
24536794267 cycles #
4006425.858 GHz ( +- 0.19% ) (83.31%)
1676085087 stalled-cycles-frontend # 6.83% frontend cycles idle ( +- 0.46% ) (83.32%)
13035595603 stalled-cycles-backend # 53.13% backend cycles idle ( +- 0.16% ) (33.36%)
18260877653 instructions # 0.74 insn per cycle
# 0.71 stalled cycles per insn ( +- 0.05% ) (50.03%)
4112411983 branches #
671484364.603 M/sec ( +- 0.03% ) (66.68%)
114066929 branch-misses # 2.77% of all branches ( +- 0.11% ) (83.32%)
6.1278 +- 0.0121 seconds time elapsed ( +- 0.20% )
```
This tells us that the actual `-analysis-inconsistencies-output-file=` outputting only takes ~0.4 sec for 43970 benchmark points (3 whole sweeps)
(Also, wow this is fast, it used to take several minutes originally)
Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=40715 | PR40715 ]].
Reviewers: courbet, gchatelet
Reviewed By: courbet
Subscribers: tschuett, jdoerfert, llvm-commits, RKSimon
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D58355
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354441
91177308-0d34-0410-b5e6-
96231b3b80d8
projects / llvm / commit