Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754476AbZFHIO6 (ORCPT ); Mon, 8 Jun 2009 04:14:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753241AbZFHIOo (ORCPT ); Mon, 8 Jun 2009 04:14:44 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:52210 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752879AbZFHIOn (ORCPT ); Mon, 8 Jun 2009 04:14:43 -0400 Date: Mon, 8 Jun 2009 10:14:39 +0200 From: Ingo Molnar To: Dave Young Cc: Linux Kernel Mailing List , Andrew Morton , Linus Torvalds Subject: Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase Message-ID: <20090608081439.GB6372@elte.hu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2073 Lines: 55 * Dave Young wrote: > Add a halt_delay module parameter in printk.c used to read the > printk messages in halt/poweroff/restart phase, delay each printk > messages by halt_delay milliseconds. It is useful for debugging if > there's no other way to dump kernel messages that time. > > The halt_delay max value is 65535, default value is 0, change it > by: > > echo xxx > /sys/module/printk/parameters/halt_delay > > Signed-off-by: Dave Young > --- > Documentation/kernel-parameters.txt | 5 +++++ > kernel/printk.c | 17 +++++++++++++++++ > 2 files changed, 22 insertions(+) > > --- linux-2.6.orig/kernel/printk.c 2009-06-08 13:55:35.000000000 +0800 > +++ linux-2.6/kernel/printk.c 2009-06-08 13:56:23.000000000 +0800 > @@ -250,6 +250,22 @@ static inline void boot_delay_msec(void) > } > #endif > > +/* msecs delay after each halt/poweroff/restart phase printk, > + unsigned short is enough for delay in milliseconds */ > +static unsigned short halt_delay; > + > +static inline void halt_delay_msec(void) > +{ > + if (unlikely(halt_delay == 0 || !(system_state == SYSTEM_HALT > + || system_state == SYSTEM_POWER_OFF > + || system_state == SYSTEM_RESTART))) > + return; This is a tiny bit ugly (and goes into the vprintf path) but i can see no other way either - a system_state > SYSTEM_RUNNING check would needlessly include the suspend-to-disk state (which we dont want to include here). In theory we could turn system_state into a bitmask and have a print_delay_mask check instead of these flags ... but that is a far wider change and i'm not sure it's a net step forwards. I've applied your patch to tip:core/printk with small edits to the changelog - Linus & Andrew is Cc:ed, should they have any objections. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/