Re: [PATCH 08/14] lib/Kconfig: introduce FAST_PATH option

Andy Shevchenko
2021-02-18T18:01:31Z

On Wed, Feb 17, 2021 at 08:05:06PM -0800, Yury Norov wrote:
> This series introduces fast paths for find_bit() routines. It is
> beneficial for typical systems, but those who limited in I-cache
> may be concerned about increasing the .text size of the Image.
>
> To address this concern, one can disable FAST_PATH option in the config
> and some save memory.
>
> The effect of this option on my arm64 next-20210217 build is:

(Maybe bloat-o-meter will give better view on this, i.e. more human-readable)

> Before:
> Sections:
> Idx Name Size VMA LMA File off Algn
> 0 .head.text 00010000 ffff800010000000 ffff800010000000 00010000 2**16
> CONTENTS, ALLOC, LOAD, READONLY, CODE
> 1 .text 0115e3a8 ffff800010010000 ffff800010010000 00020000 2**16
> CONTENTS, ALLOC, LOAD, READONLY, CODE
> 2 .got.plt 00000018 ffff80001116e3a8 ffff80001116e3a8 0117e3a8 2**3
> CONTENTS, ALLOC, LOAD, DATA
> 3 .rodata 007a72ca ffff800011170000 ffff800011170000 01180000 2**12
> CONTENTS, ALLOC, LOAD, DATA
> ...
>
> After:
> Sections:
> Idx Name Size VMA LMA File off Algn
> 0 .head.text 00010000 ffff800010000000 ffff800010000000 00010000 2**16
> CONTENTS, ALLOC, LOAD, READONLY, CODE
> 1 .text 011623a8 ffff800010010000 ffff800010010000 00020000 2**16
> CONTENTS, ALLOC, LOAD, READONLY, CODE
> 2 .got.plt 00000018 ffff8000111723a8 ffff8000111723a8 011823a8 2**3
> CONTENTS, ALLOC, LOAD, DATA
> 3 .rodata 007a772a ffff800011180000 ffff800011180000 01190000 2**12
> CONTENTS, ALLOC, LOAD, DATA
> ...
>
> Notice that this is the cumulive effect on already existing fast paths
> controlled by SMALL_CONST() together with ones added by this series.

...

> +config FAST_PATH

I think the name is to broad for this cases, perhaps BITS_FAST_PATH? or BITMAP?

> + bool "Enable fast path code generation"
> + default y
> + help
> + This option enables fast path optimization with the cost of increasing
> + the text section.

--
With Best Regards,
Andy Shevchenko