[PATCH] x86: Pack function addresses tightly as well

[Ingo Molnar]

* 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.

Thanks,

	Ingo

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