google/benchmark

[BUG] ARM big.LITTLE boards report wrong cpu count and frequency

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#1,385 opened on 2022年4月27日

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bughelp wanted

説明

Describe the bug On big.LITTLE ARM systems the displayed frequency and corresponding cpu count are wrong.

System Which OS, compiler, and compiler version are you using:

  • OS: Debian
  • Compiler and version: clang-12

To reproduce Link a binary against libbenchmark and run it Example output:

Running ./dojo_bench
Run on (6 X 1512 MHz CPU s)
Load Average: 0.10, 0.19, 0.77

Expected behavior Print the highest cpu frequency of all available cores, because the benchmark is always ran there.

Running ./dojo_bench
Run on (2 X 2016 MHz CPU s and 4 X 1512 MHz CPU s)
Load Average: 0.10, 0.19, 0.77

Additional context

for i in {0..5}; do cat /sys/devices/system/cpu/cpu"$i"/cpufreq/scaling_max_freq; done
1512000
1512000
1512000
1512000
2016000
2016000

The benchmark is always ran either on cpu 4 or 5. Shutting down last 2 cores causes benchmark times to drop significantly, proving that the "1512 MHz" core is never used.

コントリビューターガイド

技術スタック
cpp
領域
performance
Issue 種別
bug
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
half day
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
Familiarity with C++Linux sysfs file systemUnderstanding of CPU affinity
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
60
調査方針
Examine the code in `src/sysinfo.cc` for CPU frequency detection. The fix should iterate over all CPUs, read `scaling max freq` from sysfs, group CPUs by frequency, and print the count per frequency cluster (e.g., '2 X 2016 MHz CPU s and 4 X 1512 MHz CPU s'). See the expected output in the issue description.
[BUG] ARM big.LITTLE boards report wrong cpu count and frequency · google/benchmark#1385 | Good First Issue