[PATCH] x86: Pack function addresses tightly as well
From: Ingo Molnar
Date: Fri Apr 10 2015 - 08:18:18 EST
* Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> I realize that x86 CPU manufacturers recommend 16-byte jump target
> alignments (it's in the Intel optimization manual), but the cost of
> that is very significant:
> text data bss dec filename
> 12566391 1617840 1089536 15273767 vmlinux.align.16-byte
> 12224951 1617840 1089536 14932327 vmlinux.align.1-byte
> By using 1 byte jump target alignment (i.e. no alignment at all) we
> get an almost 3% reduction in kernel size (!) - and a probably
> similar reduction in I$ footprint.
Likewise we could pack functions tightly as well via the patch below:
text data bss dec filename
12566391 1617840 1089536 15273767 vmlinux.align.16-byte
12224951 1617840 1089536 14932327 vmlinux.align.1-byte
11976567 1617840 1089536 14683943 vmlinux.align.1-byte.funcs-1-byte
Which brings another 2% reduction in the kernel's code size.
It would be interesting to see some benchmarks with these two patches
applied. Only lightly tested.