From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E050CD80DE for ; Tue, 10 Oct 2023 14:13:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232605AbjJJONI (ORCPT ); Tue, 10 Oct 2023 10:13:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229562AbjJJONG (ORCPT ); Tue, 10 Oct 2023 10:13:06 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E8D7C99 for ; Tue, 10 Oct 2023 07:13:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=oT8vyW0rcd9dmGUW7gq6FLmT8hw5IrIbn9c99vaOk+A=; b=OmaQV/tP8+GGn+Nwl/ceaJ9lDN xnXTNTwHFX5gBNgoCOm704oPcIozMgB643BZJC3PxZwwQ8u+B0jrHKzk9VovmyCK2DDU7pNtPO63Y 9ljMIeQ5rjXrtfmYgQ0Gprhj7EjWrpjRysRoXEZInM2unJFKsLaNIfLbDlCr3U/1jje+/mR2quocX NDeHg6xiSXjCKC3a/tkNreYY0uRB1KtcRfVo9aNINZs9gsXiE5KN/Ei8dbNMT5Zigl+TAmuc1aY94 PYP0t59ZZhJfXnfVz+SQ5e0GfiqIsh6EnnsAR4rTw9yygQZwJ85tboKrPLx8PuPRFe8//uACoUXsk RXK8UiGA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1qqDTX-00GtuQ-36; Tue, 10 Oct 2023 14:12:45 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CA283300392; Tue, 10 Oct 2023 16:12:44 +0200 (CEST) Date: Tue, 10 Oct 2023 16:12:44 +0200 From: Peter Zijlstra To: Phil Auld Cc: Chen Yu , Ingo Molnar , Juri Lelli , Vincent Guittot , Biju Das , Marek Szyprowski , linux-kernel@vger.kernel.org, Tim Chen , Chen Yu Subject: Re: [PATCH] sched/fair: Use printk_deferred instead of printk in pick_eevdf() Message-ID: <20231010141244.GM377@noisy.programming.kicks-ass.net> References: <20231010032541.339606-1-yu.c.chen@intel.com> <20231010075928.GA377@noisy.programming.kicks-ass.net> <20231010122600.GA477540@lorien.usersys.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231010122600.GA477540@lorien.usersys.redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 10, 2023 at 08:26:00AM -0400, Phil Auld wrote: > > No.. I detest printk_deferred with a passion. This is effectively a WARN > > and we don't do silly buggers for them either. > > > > Sure, printk_deferred is not ideal, but is getting this message in the right > order worth locking up people's machines? Not sure you get the message at > all when that happens. I have to dig the code location out of the crash > dump to find which sched warning fired and took down the (usually virtual) > machine. Same thing with WARN(), we don't have a silly bugger version of that either. Just use a sane printk() / console or whatever. Virt stuff has perfectly functional serial consoles that works just fine and don't lock up the machine -- mostly. Use my early_printk hacks if you want something reliable: https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=debug/experimental Boot with: "earlyprintk=serial,ttyS0,115200 force_early_printk". And all will be well. The fact that crashdump is more reliable than printk is a *BIG* problem and the only solution is fixing printk() (people are sorta working on that). We should not try and work around this problem. I fundamentally despise the delayed stuff, I've had countless insteances where delaying output means you have no output because the machine is dead.