riscv_dis_opts_batch_1

Disassembler: Core improvements and optimizations (batch 1)

• Branch: riscv-dis-opts-batch-1
• Tracking PR: #28 (view Pull Request and Diff)
• Mailing List:
  • Not yet

Conflicts With

• Pending: Disassembler: Implement "generic subsets" (PATCH v1 only)
  It also changes the core disassembler. Note that the latest version depends on this patchset.
• Pending (RFC): Disassembler: Check shift amount against XLEN (Idea 1)
  It also changes the core disassembler.

Based On

• Disassembler: Use faster hash table
• Disassembler: Minor optimizations (batch 1)
• Disassembler: Cache instruction class support
• Disassembler: Use xlen on ADDIW address sequence

Feature Description

(TODO)

Benchmarking System

This benchmark is performed on:

• Ubuntu 22.04 LTS
• AMD Ryzen 5 PRO 5650G processor

In the parallel run, I ran 6 parallel jobs with -j6 (corresponding 6 cores; although the processor has 12 hardware threads, -j12 just slowed the benchmark).

Aggregate Performance Improvements

On disassembling linked RISC-V ELF programs using objdump, performance improvements achieved by this project is usually about 25-32%. Isn't it nice to have?

Note that a few percent may be compensated by future non-performance changes. In fact, some performance changes for objdump -d hurts GDB performance a bit because of extra initialization (which is caused per instruction on the current GDB design).

This is relative to the latest master (commit 8e883b5e112).

objdump -d (ELF)

Program	Improvements	Notes
Busybox 1.35.1 (RV64GC)	29.0-32.8%
OpenSBI 1.1 (generic fw_*.elf)	42.3-42.5%
Linux kernel 5.18 (vmlinux)	27.3-29.2%
Linux kernel 5.18 (vmlinux.o)	2.5-14.8%	Not finally linked
glibc (libc.so.6)	26.7-30.5%

Due to extra overhead handling many debugging information and symbols, disassembling *.o will be relatively slower.

objdump -d (ELF-based archive)

Program	Improvements
glibc (libc.a)	6.5-7.2%
newlib (libc.a)	7.0-10.6%

Due to extra archive file handling, disassembler performance improvements are not large enough.

objdump -D (binary)

Program	Improvements
Linux kernel 5.18 (vmlinux)	73.3-101.1%
Random files (/dev/urandom)	91.9-113.9%
1M (1048576) CSR instructions	374.1%

gdb: disas of near all code region

Program	Improvements
Linux kernel 5.18 (vmlinux) with debug info	30.8%
Linux kernel 5.18 (vmlinux) without debug info	91.6%
OpenSBI 1.1 (generic fw_*.elf)	80.0-80.5%
1M (1048576) CSR instructions (ELF)	220.1%

Batch: objdump -d on Linux distribution

Serial Run: All /usr/bin Programs

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	563	25.2%
Debian unstable (as of 2022-07-20)	269	25.4%

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

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	100	13.0%
Debian unstable (as of 2022-07-20)	100	5.0%

Parallel Run: All (including data-only ELFs)

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	7666	13.4%
Debian unstable (as of 2022-07-20)	946	6.8%

Batch: objdump -D (as binary) on Linux distribution

Serial Run: All /usr/bin Programs

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	563	50.0%
Debian unstable (as of 2022-07-20)	269	42.1%

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

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	100	70.5%
Debian unstable (as of 2022-07-20)	100	50.0%

Parallel Run: All (including data-only ELFs)

System	N	Improvements
Ubuntu 22.04 LTS (image for HiFive Unmatched)	7666	56.2%
Debian unstable (as of 2022-07-20)	946	43.6%