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Performance Regression in QEMU (amd64 Emulating LoongArch64) from 8.0.4 to 9.0.2
Description of problem:
Previous Performance: In May 2023, we were using QEMU 8.0.4 for qemu-user emulation, and the performance was satisfactory. The setup did not include LSX (Loongson SIMD Extensions) support in either the system or QEMU. Performance results are shown in Figure A.
Current Performance: Recently, we upgraded to QEMU 9.0.2. Both the system and QEMU now support vectorized instruction sets. However, we observed a performance decline to less than 60% of the previous benchmarks.
We found that the slowdown is not caused by LSX. Disabling LSX compilation in the new version results in even worse performance. However, there are indeed significant differences between the two systems in terms of LSX support.
Additional information:
We use systemd-nspawn and qemu-binfmt for containerized operations. You can get a clean chroot from lcpu release [here](https://github.com/lcpu-club/loongarchlinux-dockerfile/releases/download/20240806/base-devel-loong64-20240806.tar.zst)
Figure A, performance in May 2023
Figure B, performance nowadays
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