Re: [for-next][PATCH 04/26] bootconfig: Add Extra Boot Config support

From: Geert Uytterhoeven
Date: Thu Feb 06 2020 - 12:20:33 EST


Hi Hiramatsu-san,

On Thu, Feb 6, 2020 at 3:42 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> On Thu, 6 Feb 2020 12:54:05 +0100
> Borislav Petkov <bp@xxxxxxxxx> wrote:
> > On Tue, Jan 14, 2020 at 04:03:20PM -0500, Steven Rostedt wrote:
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index a34064a031a5..63450d3bbf12 100644
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1215,6 +1215,17 @@ source "usr/Kconfig"
> > >
> > > endif
> > >
> > > +config BOOT_CONFIG
> > > + bool "Boot config support"
> > > + select LIBXBC
> > > + default y
> >
> > Any particular reason this is default y? Why should it be enabled by
> > default on all boxes?
>
> Oh, you are not the first person asked that :)
>
> https://lkml.org/lkml/2019/12/9/563
>
> And yes, I think this is important that will useful for most developers
> and admins. Since the bootconfig already covers kernel and init options,
> this can be a new standard way to pass args to kernel boot.
>
> And as I reported above thread, the memory footpoint of view, most code
> and working memory are released after boot. Also, as Linus's suggested,
> now this feature is enabled only if user gives "bootconfig" on the kernel
> command line. So the side effect is minimized.

With m68k/atari_defconfig, bloat-o-meter says:

add/remove: 39/0 grow/shrink: 2/0 up/down: 13086/0 (13086)

which is IMHO not that small for a "default y" option that may or may not
be used.

Especially:

Function old new delta
xbc_nodes - 8192 +8192

Any chance xbc_nodes can be allocated dynamically, and only when needed?

Yes, there are industrial products running Linux on a current ARM SoC
using the builtin 8 or 10 MiB of SRAM (+ XIP for the kernel), so these
definitely want to say CONFIG_BOOT_CONFIG=n.

Thanks!

add/remove: 39/0 grow/shrink: 2/0 up/down: 13086/0 (13086)
Function old new delta
xbc_nodes - 8192 +8192
xbc_init - 854 +854
start_kernel 1020 1580 +560
copy_xbc_key_value_list - 362 +362
__xbc_parse_value - 324 +324
xbc_snprint_cmdline - 294 +294
xbc_node_compose_key_after - 266 +266
xbc_namebuf - 256 +256
xbc_add_sibling - 254 +254
xbc_node_find_next_leaf - 186 +186
xbc_node_find_child - 176 +176
__xbc_add_key - 162 +162
proc_boot_config_init - 124 +124
xbc_make_cmdline - 122 +122
xbc_node_find_value - 104 +104
xbc_node_find_next_key_value - 102 +102
__xbc_close_brace - 92 +92
find_match_node - 80 +80
__xbc_parse_keys - 78 +78
xbc_node_get_data - 64 +64
xbc_parse_key - 60 +60
skip_comment - 48 +48
xbc_destroy_all - 42 +42
xbc_node_get_parent - 38 +38
xbc_parse_error - 36 +36
xbc_node_get_child - 34 +34
xbc_node_get_next - 32 +32
boot_config_checksum - 30 +30
boot_config_proc_show - 26 +26
xbc_root_node - 20 +20
kzalloc.constprop 810 830 +20
xbc_node_index - 14 +14
xbc_node_num - 4 +4
xbc_data_size - 4 +4
xbc_data - 4 +4
saved_boot_config - 4 +4
last_parent - 4 +4
extra_init_args - 4 +4
extra_command_line - 4 +4
__initcall_proc_boot_config_init5 - 4 +4
xbc_debug_dump - 2 +2
Total: Before=3688860, After=3701946, chg +0.35%

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds