riscv_dis_opts_cache_support

Disassembler: Cache instruction class support

• Status: Waiting for a prerequisite to be Merged
• Branch: riscv-dis-opts-cache-support
• Tracking PR: #22 (view Pull Request and Diff)
• Mailing List:
  • Not yet

Requires

• Disassembler: Minor optimizations (batch 1)
  • Requires: Disassembler: Use faster hash table

Project: Disassembler Performance Improvements

Aggregate performance benchmark should be available here.

1. Disassembler: Use faster hash table
2. Disassembler: Minor optimizations (batch 1)
3. (You are here) Disassembler: Cache instruction class support

Feature Description

As I mentioned in the previous patchset, calling riscv_subset_supports repeatedly harms the performance in a measurable way (about 3-13% in total).

As a simple solution, this patch now caches instruction class support as a signed char array.

Performance Improvements

On disassembling linked RISC-V ELF files using objdump, performance improvements achieved by this patchset is about 5-6%. Not bad for a simple change.

This is relative to the previous optimization.

objdump -d (ELF)

Program	Improvements	Notes
Busybox 1.35.1 (RV64GC)	5.5-6.2%
OpenSBI 1.1 (generic fw_*.elf)	6.1-6.5%
Linux kernel 5.18 (vmlinux)	5.1-5.6%
Linux kernel 5.18 (vmlinux.o)	0.1-1.9%	Not finally linked
glibc (libc.so.6)	5.1-5.7%

objdump -d (ELF-based archive)

Program	Improvements
glibc (libc.a)	0.9-1.0%
newlib (libc.a)	1.1-1.9%

objdump -D (binary)

Program	Improvements
Linux kernel 5.18 (vmlinux)	6.5-7.0%
Random files (/dev/urandom)	7.0-7.5%
1M (1048576) CSR instructions	38.4%

gdb: disas of near all code region

Program	Improvements
Linux kernel 5.18 (vmlinux) with debug info	-1.7%
Linux kernel 5.18 (vmlinux) without debug info	-1.5%
OpenSBI 1.1 (generic fw_*.elf)	(-0.8)-(-0.5)%
1M (1048576) CSR instructions (ELF)	5.1%

Batch: objdump -d on Linux distribution

Serial Run: All /usr/bin Programs

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	563	5.0%
Debian unstable (as of 2022-07-20)	269	4.9%

Parallel Run: Top 100 in Size (including data-only ELFs)

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	100	2.5%
Debian unstable (as of 2022-07-20)	100	0.7%

Parallel Run: All (including data-only ELFs)

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	7666	2.3%
Debian unstable (as of 2022-07-20)	946	0.5%