Re: [PATCH v3 4/4] printk/nmi: Increase the size of NMI buffer and make it configurable
From: Andrew Morton
Date: Fri Dec 11 2015 - 17:58:00 EST
On Fri, 11 Dec 2015 13:41:59 +0100 Petr Mladek <pmladek@xxxxxxxx> wrote:
> On Fri 2015-12-11 12:10:02, Geert Uytterhoeven wrote:
> > On Wed, Dec 9, 2015 at 2:21 PM, Petr Mladek <pmladek@xxxxxxxx> wrote:
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -866,6 +866,28 @@ config LOG_CPU_MAX_BUF_SHIFT
> > > 13 => 8 KB for each CPU
> > > 12 => 4 KB for each CPU
> > >
> > > +config NMI_LOG_BUF_SHIFT
> > > + int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
> > > + range 10 21
> > > + default 13
> > > + depends on PRINTK && HAVE_NMI
> > Symbol NMI_LOG_BUF_SHIFT does not exist if its dependencies are not met.
> __h, the NMI buffer is enabled on arm via NEED_PRINTK_NMI.
> The buffer is compiled when CONFIG_PRINTK_NMI is defined. I am going
> to fix it the following way:
> diff --git a/init/Kconfig b/init/Kconfig
> index efcff25a112d..61cfd96a3c96 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -870,7 +870,7 @@ config NMI_LOG_BUF_SHIFT
> int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)"
> range 10 21
> default 13
> - depends on PRINTK && HAVE_NMI
> + depends on PRINTK_NMI
> Select the size of a per-CPU buffer where NMI messages are temporary
> stored. They are copied to the main log buffer in a safe context
I'm wondering why we're building kernel/printk/nmi.o if HAVE_NMI is not
obj-$(CONFIG_PRINTK_NMI) += nmi.o
depends on PRINTK
depends on HAVE_NMI || NEED_PRINTK_NMI
This is a bit messy. NEED_PRINTK_NMI is an added-on hack for one
particular arm variant. From the changelog:
"One exception is arm where the deferred printing is used for
printing backtraces even without NMI. For this purpose, we define
NEED_PRINTK_NMI Kconfig flag. The alternative printk_func is
explicitly set when IPI_CPU_BACKTRACE is handled."
- why does arm needs deferred printing for backtraces?
- why is this specific to CONFIG_CPU_V7M?
- can this Kconfig logic be cleaned up a bit?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/