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Date: Fri, 7 Feb 2020 09:30:03 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Borislav Petkov <bp@...en8.de>,
Steven Rostedt <rostedt@...dmis.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [for-next][PATCH 04/26] bootconfig: Add Extra Boot Config
support
On Thu, 6 Feb 2020 18:20:15 +0100
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Hiramatsu-san,
>
> On Thu, Feb 6, 2020 at 3:42 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > On Thu, 6 Feb 2020 12:54:05 +0100
> > Borislav Petkov <bp@...en8.de> 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, I think we can use memblock to allocate it. However, this xbc_nodes is
__init_data, which is released right after boot. So I think it should be
OK except for your system doesn't have user space...
> 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.
I think for such products the kernel must be tuned with custom config,
and you can say CONFIG_BOOT_CONFIG=n. That is a configurable feature.
Thank you,
>
> 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@...ux-m68k.org
>
> 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
--
Masami Hiramatsu <mhiramat@...nel.org>
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