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 AFEDBC433EF for ; Fri, 20 May 2022 16:06:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351329AbiETQGr (ORCPT ); Fri, 20 May 2022 12:06:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351323AbiETQGp (ORCPT ); Fri, 20 May 2022 12:06:45 -0400 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9C27E1737DC for ; Fri, 20 May 2022 09:06:44 -0700 (PDT) Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1ns598-0001eJ-0c; Fri, 20 May 2022 12:06:34 -0400 Message-ID: <7c57004c1f9a2580b34ea6708065260ec2706122.camel@surriel.com> Subject: Re: [RFC PATCH v2] printk: console: Allow each console to have its own loglevel From: Rik van Riel To: Chris Down , linux-kernel@vger.kernel.org Cc: Petr Mladek , Greg Kroah-Hartman , Sergey Senozhatsky , Steven Rostedt , John Ogness , Geert Uytterhoeven , kernel-team@fb.com Date: Fri, 20 May 2022 12:06:33 -0400 In-Reply-To: References: Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-ubMqwuwXY5KJJLvOxJq9" User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 Sender: riel@shelob.surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-ubMqwuwXY5KJJLvOxJq9 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2022-05-20 at 13:57 +0100, Chris Down wrote: > [Once the goals of this patch are generally agreed upon, it can be > split > out further with more detailed changelogs if desired.] >=20 > Consoles can have vastly different latencies and throughputs. For > example, writing a message to the serial console can take on the > order > of tens of milliseconds to get the UART to successfully write a > message. > While this might be fine for a single, one-off message, this can > cause > significant application-level stalls in situations where the kernel > writes large amounts of information to the console. >=20 It's more than just application-level stalls. I have seen some cases of the kernel spending so much time logging things to serial console that it thinks it locked up, and panics as a result of how slow the serial console is. Adding insult to injury, because the log level is sytem wide, we only see _some_ of the hints of why the kernel started spewing like that in the netcons logs. If we print all the information, we will have more hosts panic because we spent too much time in the serial console code. If we print less information, we won't find out some of the other things causing issues on systems. Having per console log levels will allow us to avoid the serial console issues, and gather all the info we need on other stuff happening on the system. --=20 All Rights Reversed. --=-ubMqwuwXY5KJJLvOxJq9 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAmKHvIkACgkQznnekoTE 3oPluwgAgd1aI2eHB0PNcmJzACgNDCZRTTPFVakAgsImqCCrJ5IUkquQso2VAXZU bE4ElQQWEuXwJaPbR/vQprD6619dmVjObAabS/plvaba1WhxGVp/qdFMbqCPI/QI At21/ar8mC65RK/gdV4h/7FRMhd85AfpXGXVfuW1Fq5mpGMG00Gtwp4EtkCJV8nh MqJHM2pJK9vY0jZAEGECX3Oj9XpZKAhf5W/ldt5n794LAf56GbnTmHyFwPd78YjY cfAFmJ0/SLg2x5znMLt5sJAcvEMhzZz6zAR2IdsNyxlb9nmtoCnCNdtsqdIkiibj LbPSGBM/WcHG4trXnJZWYJOUts5PtQ== =pfnw -----END PGP SIGNATURE----- --=-ubMqwuwXY5KJJLvOxJq9--