From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752617AbcGFDNY (ORCPT ); Tue, 5 Jul 2016 23:13:24 -0400 Received: from darkcity.gna.ch ([195.226.6.51]:56864 "EHLO mail.gna.ch" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751923AbcGFDNW (ORCPT ); Tue, 5 Jul 2016 23:13:22 -0400 Subject: Re: [PATCH] drm/radeon: Remove deprecated create_singlethread_workqueue To: Tejun Heo References: <20160702110350.GA3601@Karyakshetra> <20160702134614.GB17431@htj.duckdns.org> <9e69b1fd-eb93-1fee-15af-c905ee3a202f@daenzer.net> <20160705210644.GB25394@htj.duckdns.org> Cc: Bhaktipriya Shridhar , Alex Deucher , =?UTF-8?Q?Christian_K=c3=b6nig?= , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org From: =?UTF-8?Q?Michel_D=c3=a4nzer?= Message-ID: <936c5bae-b8e6-bf64-8be2-d27608814fac@daenzer.net> Date: Wed, 6 Jul 2016 12:12:52 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.1.0 MIME-Version: 1.0 In-Reply-To: <20160705210644.GB25394@htj.duckdns.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 On 06.07.2016 06:06, Tejun Heo wrote: > On Mon, Jul 04, 2016 at 12:58:32PM +0900, Michel Dänzer wrote: >> On 02.07.2016 22:46, Tejun Heo wrote: >>> On Sat, Jul 02, 2016 at 04:33:50PM +0530, Bhaktipriya Shridhar wrote: >>>> alloc_workqueue replaces deprecated create_singlethread_workqueue(). >>>> >>>> A dedicated workqueue has been used since work items need to be flushed >>>> as a group rather than individually. > > There seem to be two work items involved, the flip one and unpin one. > Provided that there's no ordering requirement between the two, can't > we just flush them individually? There is an ordering requirement between the two queues, but it's enforced by the driver (by only queuing the unpin work once a flip has completed, which only happens after the corresponding flip work has run). Not being very familiar with the workqueue APIs, I'll describe how it's supposed to work from a driver POV, which will hopefully help you guys decide on the most appropriate alloc_workqueue parameters. There is one flip work queue for each hardware CRTC. At most one radeon_flip_work_func item can be queued for any of them at any time. When a radeon_flip_work_func item is queued, it should be executed ASAP (so WQ_HIGHPRI might be appropriate?). In contrast, the radeon_unpin_work_func items aren't particularly urgent, and it's okay for several of them to be queued up. So I guess it would actually make sense to use a different workqueue for them, maybe even the default one? >>>> Since there are only a fixed number of work items, explicit concurrency >>>> limit is unnecessary here. >>> >>> What are the involved work items? >> >> drivers/gpu/drm/radeon/radeon_display.c:radeon_flip_work_func() >> >>> Is it safe to run them concurrently? >> >> Concurrently with what exactly? > > The flip and unpin work items. Yes, it's safe to run those concurrently. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer