From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-x22c.google.com (mail-ob0-x22c.google.com [IPv6:2607:f8b0:4003:c01::22c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 5A09F1A0657 for ; Fri, 11 Dec 2015 22:10:05 +1100 (AEDT) Received: by obc18 with SMTP id 18so80281498obc.2 for ; Fri, 11 Dec 2015 03:10:02 -0800 (PST) MIME-Version: 1.0 Sender: geert.uytterhoeven@gmail.com In-Reply-To: <1449667265-17525-5-git-send-email-pmladek@suse.com> References: <1449667265-17525-1-git-send-email-pmladek@suse.com> <1449667265-17525-5-git-send-email-pmladek@suse.com> Date: Fri, 11 Dec 2015 12:10:02 +0100 Message-ID: Subject: Re: [PATCH v3 4/4] printk/nmi: Increase the size of NMI buffer and make it configurable From: Geert Uytterhoeven To: Petr Mladek Cc: Andrew Morton , Peter Zijlstra , Steven Rostedt , Russell King , Daniel Thompson , Jiri Kosina , Ingo Molnar , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "the arch/x86 maintainers" , "linux-arm-kernel@lists.infradead.org" , "adi-buildroot-devel@lists.sourceforge.net" , Cris , Linux MIPS Mailing List , "linuxppc-dev@lists.ozlabs.org" , linux-s390 , Linux-sh list , sparclinux Content-Type: text/plain; charset=UTF-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Dec 9, 2015 at 2:21 PM, Petr Mladek 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. > + help > + 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 > + to avoid a deadlock. The value defines the size as a power of 2. > + > + NMI messages are rare and limited. The largest one is when > + a backtrace is printed. It usually fits into 4KB. Select > + 8KB if you want to be on the safe side. > + > + Examples: > + 17 => 128 KB for each CPU > + 16 => 64 KB for each CPU > + 15 => 32 KB for each CPU > + 14 => 16 KB for each CPU > + 13 => 8 KB for each CPU > + 12 => 4 KB for each CPU > + > # > # Architectures with an unreliable sched_clock() should select this: > # > diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c > index 5465230b75ec..78c07d441b4e 100644 > --- a/kernel/printk/nmi.c > +++ b/kernel/printk/nmi.c > @@ -41,7 +41,8 @@ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; > static int printk_nmi_irq_ready; > atomic_t nmi_message_lost; > > -#define NMI_LOG_BUF_LEN (4096 - sizeof(atomic_t) - sizeof(struct irq_work)) > +#define NMI_LOG_BUF_LEN ((1 << CONFIG_NMI_LOG_BUF_SHIFT) - \ > + sizeof(atomic_t) - sizeof(struct irq_work)) kernel/printk/nmi.c:50:24: error: 'CONFIG_NMI_LOG_BUF_SHIFT' undeclared here (not in a function) E.g. efm32_defconfig http://kisskb.ellerman.id.au/kisskb/buildresult/12565754/ Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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