From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from [195.159.176.226] ([195.159.176.226]:57274 "EHLO blaine.gmane.org" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751848AbdDKPkL (ORCPT ); Tue, 11 Apr 2017 11:40:11 -0400 Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1cxxti-00048l-Pg for linux-block@vger.kernel.org; Tue, 11 Apr 2017 17:40:02 +0200 To: linux-block@vger.kernel.org From: Holger =?iso-8859-1?q?Hoffst=E4tte?= Subject: Re: WBT for SQ devices interface Date: Tue, 11 Apr 2017 15:16:16 +0000 (UTC) Message-ID: References: <20170411093827.GC2471@quack2.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Tue, 11 Apr 2017 11:38:27 +0200, Jan Kara wrote: > when testing my fix for 0-day reports with writeback throttling I came > across somewhat unexpected behavior with user interface of writeback > throttling. So currently if CFQ is used as an IO scheduler, we disable > writeback throttling because they don't go well together. However when user > has CONFIG_BLK_WBT_SQ=y and switches IO scheduler to NOOP or DEADLINE > writeback throttling still stays disabled. This is somewhat unexpected > especially because the switching of IO scheduler from CFQ to something else > can have happened behind user's back by some udev rule or so. So basically > CONFIG_DEFAULT_CFQ=y and CONFIG_BLK_WBT_SQ=y don't make sense together. :( > So do people thing we should enable WBT if CONFIG_BLK_WBT_SQ=y and IO > scheduler is switched from CFQ to something else? Yes please. If a scheduler doesn't like WBT then that is its own problem. Deadline with WBT has worked fine for me. -h