Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756674AbZFIBB1 (ORCPT ); Mon, 8 Jun 2009 21:01:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751776AbZFIBBT (ORCPT ); Mon, 8 Jun 2009 21:01:19 -0400 Received: from mail-ew0-f210.google.com ([209.85.219.210]:42802 "EHLO mail-ew0-f210.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751478AbZFIBBT convert rfc822-to-8bit (ORCPT ); Mon, 8 Jun 2009 21:01:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=jRWyQ1iTwC1xLZ6vku0bz8ciRMsp6f05w/JD41X2Tw2R+exYc+y+dYtYWcrqixaR8o rJaYKC/24UK0mfMSqPS8A6nfHOJuayxacny8NMk7E5QMdNtn3uJGigs3YesQ0RbZNkCR 9ijqUg8YvVITD/20xU3n8c/AejN0Wx668FjRw= MIME-Version: 1.0 In-Reply-To: <20090608143913.749e19c5.akpm@linux-foundation.org> References: <20090608081439.GB6372@elte.hu> <20090608012845.9c428525.akpm@linux-foundation.org> <20090608084807.GE6372@elte.hu> <20090608092607.8b331bf0.akpm@linux-foundation.org> <20090608171501.GA15399@elte.hu> <20090608143913.749e19c5.akpm@linux-foundation.org> Date: Tue, 9 Jun 2009 09:01:19 +0800 Message-ID: Subject: Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase From: Dave Young To: Andrew Morton Cc: Ingo Molnar , linux-kernel@vger.kernel.org, torvalds@linux-foundation.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2335 Lines: 64 On Tue, Jun 9, 2009 at 5:39 AM, Andrew Morton wrote: > On Mon, 8 Jun 2009 19:15:01 +0200 > Ingo Molnar wrote: > >> > questions: is it possible for interrupts to be disabled at this >> > time? If so, can we get an NMI watchdog hit? >> >> no, we generally turn off the nmi watchdog during shutdown, disable >> the lapic and io-apic, etc. > > Is x86 the only architecture which implements an NMI watchdog? > >> > Is the softlockup detector still running and if so, can it >> > trigger? >> >> in (non-emergency) reboot, last i checked, we stopped all other CPUs >> first, and then killed the current one. There's no chance for the >> watchdog thread to run. > > OK, but...  See below. > >> Anyway ... you seem to be uncomfortable about this patch - should i >> delay it for now to let it all play out? We are close to the merge >> window. > > I'm OK - I'm just bouncing ideas and questions off you guys, to make sure > that we've thought this through all the way. > > Here's another: why is it a boot option rather than a runtime-tunable? > A /proc tweakable is generally preferable because it avoids the > oh-crap-i-forgot-to-edit-grub.conf thing.  And we could perhaps then > remove all those system_state tests: userspace sets printk_delay > immediately prior to running halt/reboot/etc? Andrew, thanks your comments. I original intention is to use not boot options but sysfs interface. Do you perfer proc? without system_state testing we will have to consider the NMI watchdog and softlockup issue. > > Plus the feature becomes more general - perhaps there are use cases > where people want to slow down printks, such as: kernel goes oops, data > scrolls off, serial console/netconsole unavailable.  pause_on_oops is > supposed to help here but last time I tried it, it kinda didn't work, > plus pause_on_oops doesn't solve the data-scrolled-off problem. Seems make sense. > > Thirdly, if we do this as a general /proc/printk_delay thing, perhaps > it can be consolidated with the existing boot_delay= implementation. > -- Regards dave -- 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/