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 43E04C4332F for ; Mon, 21 Nov 2022 07:13:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229627AbiKUHNL (ORCPT ); Mon, 21 Nov 2022 02:13:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbiKUHNJ (ORCPT ); Mon, 21 Nov 2022 02:13:09 -0500 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2D0B120B9; Sun, 20 Nov 2022 23:13:08 -0800 (PST) Received: by verein.lst.de (Postfix, from userid 2407) id BA23468AA6; Mon, 21 Nov 2022 08:13:05 +0100 (CET) Date: Mon, 21 Nov 2022 08:13:05 +0100 From: Christoph Hellwig To: Jinlong Chen Cc: axboe@kernel.dk, hch@lst.de, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/2] elevator: restore old io scheduler on failure in elevator_switch Message-ID: <20221121071305.GB23882@lst.de> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 18, 2022 at 08:09:52PM +0800, Jinlong Chen wrote: > elevator_switch contains the fallback logic in sq era, but it was removed > when moving to mq (commit: a1ce35fa49852db60fc6e268038530be533c5b15), > leaving the document mismatched with the behavior. As far as I can see, > restoring the old io scheduler is more reasonable than just leaving the > scheduler none, hence there is the series. What failure scenariou can you think off where switching to the intended schedule fails, but switching back to the previous one will succeed?