On Tue, 26 Sep 2023, Arnd Bergmann wrote: > On Tue, Sep 26, 2023, at 09:14, Arnd Bergmann wrote: > > On Tue, Sep 26, 2023, at 00:33, Zhangjin Wu wrote: > > > > It would be nice to include some size numbers here for at least > > one practical use case. If you have a defconfig for a shipping > > product with a small kernel, what is the 'size -B' output you > > see comparing with and without DCE and, and with DCE+DSE? > > To follow up on this myself, for a very rough baseline, > I tried a riscv tinyconfig build with and without > CONFIG_LD_DEAD_CODE_DATA_ELIMINATION (this is currently > not supported on arm, so I did not try it there), and > then another build with simply *all* system calls stubbed > out by hacking asm/syscall-wrapper.h: > > $ size build/tmp/vmlinux-* > text data bss dec hex filename > 754772 220016 71841 1046629 ff865 vmlinux-tinyconfig > 717500 223368 71841 1012709 f73e5 vmlinux-tiny+nosyscalls > 567310 176200 71473 814983 c6f87 vmlinux-tiny+gc-sections > 493278 170752 71433 735463 b38e7 vmlinux-tiny+gc-sections+nosyscalls > 10120058 3572756 493701 14186515 d87813 vmlinux-defconfig > 9953934 3529004 491525 13974463 d53bbf vmlinux-defconfig+gc > 9709856 3500600 489221 13699677 d10a5d vmlinux-defconfig+gc+nosyscalls > > This would put us at an upper bound of 10% size savings (80kb) for > tinyconfig, which is clearly significant. For defconfig, it's > still 2.0% or 275kb size reduction when all syscalls are dropped. I did something similar a while ago. Results included here: https://lwn.net/Articles/746780/ In my case, stubbing out all syscalls produced a 7.8% reduction which was somewhat disappointing compared to other techniques. Of course it all depends on what is your actual goal. Nicolas
