From: Petr Mladek <mladek.petr@gmail.com>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
John Ogness <john.ogness@linutronix.de>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Daniel Thompson <daniel.thompson@linaro.org>
Subject: Re: [GIT PULL] printk for 5.10 (includes lockless ringbuffer)
Date: Thu, 15 Oct 2020 10:03:00 +0200 [thread overview]
Message-ID: <20201015080300.GE13775@alley> (raw)
In-Reply-To: <49292e1a-7e46-b078-d15d-fb2f406317db@rasmusvillemoes.dk>
On Wed 2020-10-14 16:58:27, Rasmus Villemoes wrote:
> On 14/10/2020 16.16, Geert Uytterhoeven wrote:
> > Hi Petr,
> >
> > On Mon, Oct 12, 2020 at 4:50 PM Petr Mladek <pmladek@suse.com> wrote:
> >> - Fully lockless ringbuffer implementation, including the support for
> >> continuous lines. It will allow to store and read messages in any
> >> situation wihtout the risk of deadlocks and without the need
> >> of temporary per-CPU buffers.
> >
> > linux-m68k-atari_defconfig$ bloat-o-meter vmlinux.old
> > vmlinux.lockless_ringbuffer
> > add/remove: 39/16 grow/shrink: 9/15 up/down: 214075/-4362 (209713)
> > Function old new delta
> > _printk_rb_static_infos - 180224 +180224
> > _printk_rb_static_descs - 24576 +24576
> > [...]
> >
> > Seriously?!? Or am I being misled by the tools?
> >
> > linux-m68k-atari_defconfig$ size vmlinux.old vmlinux.lockless_ringbuffer
> > text data bss dec hex filename
> > 3559108 941716 177772 4678596 4763c4 vmlinux.old
> > 3563922 1152496 175276 4891694 4aa42e vmlinux.lockless_ringbuffer
> >
> > Apparently not...
>
> Hm, that's quite a lot. And the only reason the buffers don't live
> entirely in .bss is because a few of their entries have non-zero
> initializers.
>
> Perhaps one could add a .init.text.initialize_static_data section of
> function pointers, with the _DEFINE_PRINTKRB macro growing something like
>
> static void __init __initialize_printkrb_##name(void) { \
> _##name##_descs[_DESCS_COUNT(descbits) - 1] = ...; \
> _##name##_infos[0] = ...; \
> _##name##_infos[_DESCS_COUNT(descbits) - 1] = ...; \
> } \
> static_data_initializer(__initialize_printkrb_##name);
>
> with static_data_initalizer being the obvious yoga for putting a
> function pointer in the .init.text.initialize_static_data section. Then
> very early in start_kernel(), probably first thing, iterate that section
> and call all the functions. But maybe that's not even early enough?
A solution might be to initialize the buffer during the first
printk() call. We could make sure that it is done in
setup_log_buf() at latest. It is called when only one CPU is
running so it should be safe. The only problem might be NMI.
Best Regards,
Petr
next prev parent reply other threads:[~2020-10-15 8:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-12 14:49 [GIT PULL] printk for 5.10 (includes lockless ringbuffer) Petr Mladek
2020-10-13 23:49 ` pr-tracker-bot
2020-10-14 14:16 ` Geert Uytterhoeven
2020-10-14 14:58 ` Rasmus Villemoes
2020-10-14 15:07 ` Geert Uytterhoeven
2020-10-15 8:03 ` Petr Mladek [this message]
2020-10-14 20:55 ` John Ogness
2020-10-15 7:52 ` Petr Mladek
2020-10-16 15:05 Petr Mladek
2020-10-16 19:54 ` pr-tracker-bot
2020-11-27 13:47 Petr Mladek
2020-11-27 19:19 ` pr-tracker-bot
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