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 <pmla...@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
