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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C5A8C2D0A8 for ; Wed, 23 Sep 2020 15:25:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C07AE206FB for ; Wed, 23 Sep 2020 15:25:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="knEE8ZNE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726603AbgIWPZw (ORCPT ); Wed, 23 Sep 2020 11:25:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42068 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726156AbgIWPZv (ORCPT ); Wed, 23 Sep 2020 11:25:51 -0400 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FD7AC0613D1 for ; Wed, 23 Sep 2020 08:25:50 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id e11so4785174wme.0 for ; Wed, 23 Sep 2020 08:25:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=AZ0TNN/4mlEawbq5kme4KBtAcxVTJOsazW2quN2exhk=; b=knEE8ZNEPhd02dhjiafNZIh6Ilcs2hRJuBBFe+Sx2gKj6V+tziP1ZYabkfgXV17TW+ NUMy2UFrZwlfmV+sdZoLINzvMUyTG87xDRqw6gwbhA534sM/HHF/4rwqLNdrpC+7QaoX qU2N+vvwVpZazeSc6YeUX68W22fba8Lj2eA+w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=AZ0TNN/4mlEawbq5kme4KBtAcxVTJOsazW2quN2exhk=; b=iUQhSRkaEQgmhk3lEA7qpNMNd1Lq7jShyEteIMddJSzPEAiGO4smTGZ8+H1MMwIeax Q2JeZKx1vy+8UPjjYxW0U1B6k19m2j25yTRTZRU0E/JM4MaPJ/heg8lFWbKO0NP1Oslx HvNzFpJFlDA5yhWhQYj18c5Txd9nvPm2PYaAKMrfFm9vEzvgwgzluRqq0RL1C0Jyw4cd La1pIGVfWtGVD8AUDflsUokcOWf0ToiLNk2TAGI2/QGyScDfn12tdS1X/OYeZVo2tHEy r1cqbTf5rqR3pjIj5pHuxj0x3BMqmg1a6V0IyA4OO3p/EoBOm1Cq2yS9eBR3Y8ckeRIb 1V/w== X-Gm-Message-State: AOAM531I+UdQlmEj2YIj5ccXEBfj3AJ+GMLy1azABNigHgmLKpnQrn2J DB3IXvpelLsQp8rPoSY5ldDQ5A== X-Google-Smtp-Source: ABdhPJwhaHjfJRQ0ck6dLHaDnam+iSpD5QCMjr6WsmrCc91FeiuFw1E8N+Fhyjg1fYBV6n1qNiQ1Mg== X-Received: by 2002:a1c:398a:: with SMTP id g132mr75865wma.41.1600874748672; Wed, 23 Sep 2020 08:25:48 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id h76sm178488wme.10.2020.09.23.08.25.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2020 08:25:47 -0700 (PDT) Date: Wed, 23 Sep 2020 17:25:45 +0200 From: Daniel Vetter To: Rob Clark Cc: Daniel Vetter , dri-devel , Rob Clark , Peter Zijlstra , linux-arm-msm , open list , Tim Murray , Tejun Heo Subject: Re: [PATCH 0/3] drm: commit_work scheduling Message-ID: <20200923152545.GQ438822@phenom.ffwll.local> Mail-Followup-To: Rob Clark , dri-devel , Rob Clark , Peter Zijlstra , linux-arm-msm , open list , Tim Murray , Tejun Heo References: <20200919193727.2093945-1-robdclark@gmail.com> <20200921092154.GJ438822@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.7.0-1-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Tue, Sep 22, 2020 at 07:48:10AM -0700, Rob Clark wrote: > On Mon, Sep 21, 2020 at 11:59 PM Daniel Vetter wrote: > > > > On Mon, Sep 21, 2020 at 5:16 PM Rob Clark wrote: > > > > > > On Mon, Sep 21, 2020 at 2:21 AM Daniel Vetter wrote: > > > > > > > > On Sat, Sep 19, 2020 at 12:37:23PM -0700, Rob Clark wrote: > > > > > From: Rob Clark > > > > > > > > > > The android userspace treats the display pipeline as a realtime problem. > > > > > And arguably, if your goal is to not miss frame deadlines (ie. vblank), > > > > > it is. (See https://lwn.net/Articles/809545/ for the best explaination > > > > > that I found.) > > > > > > > > > > But this presents a problem with using workqueues for non-blocking > > > > > atomic commit_work(), because the SCHED_FIFO userspace thread(s) can > > > > > preempt the worker. Which is not really the outcome you want.. once > > > > > the required fences are scheduled, you want to push the atomic commit > > > > > down to hw ASAP. > > > > > > > > > > But the decision of whether commit_work should be RT or not really > > > > > depends on what userspace is doing. For a pure CFS userspace display > > > > > pipeline, commit_work() should remain SCHED_NORMAL. > > > > > > > > > > To handle this, convert non-blocking commit_work() to use per-CRTC > > > > > kthread workers, instead of system_unbound_wq. Per-CRTC workers are > > > > > used to avoid serializing commits when userspace is using a per-CRTC > > > > > update loop. > > > > > > > > > > A client-cap is introduced so that userspace can opt-in to SCHED_FIFO > > > > > priority commit work. > > > > > > > > > > A potential issue is that since 616d91b68cd ("sched: Remove > > > > > sched_setscheduler*() EXPORTs") we have limited RT priority levels, > > > > > meaning that commit_work() ends up running at the same priority level > > > > > as vblank-work. This shouldn't be a big problem *yet*, due to limited > > > > > use of vblank-work at this point. And if it could be arranged that > > > > > vblank-work is scheduled before signaling out-fences and/or sending > > > > > pageflip events, it could probably work ok to use a single priority > > > > > level for both commit-work and vblank-work. > > > > > > > > The part I don't like about this is that it all feels rather hacked > > > > together, and if we add more stuff (or there's some different thing in the > > > > system that also needs rt scheduling) then it doesn't compose. > > > > > > The ideal thing would be that userspace is in control of the > > > priorities.. the setclientcap approach seemed like a reasonable way to > > > give the drm-master a way to opt in. > > > > > > I suppose instead userspace could use sched_setscheduler().. but that > > > would require userspace to be root, and would require some way to find > > > the tid. > > > > Userspace already needs that for the SCHED_FIFO for surface-flinger. > > Or is the problem that CAP_SYS_NICE is only good for your own > > processes? > > tbh, I'm not completely sure offhand what gives surfaceflinger > permission to set itself SCHED_FIFO > > (But on CrOS there are a few more pieces to the puzzle) > > > Other question I have for this is whether there's any recommendations > > for naming the kthreads (since I guess that name is what becomes the > > uapi for userspace to control this)? > > > > Otherwise I think "userspace calls sched_setscheduler on the right > > kthreads" sounds like a good interface, since it lets userspace decide > > how it all needs to fit together and compose. Anything we hard-code in > > an ioctl is kinda lost cause. And we can choose the default values to > > work reasonably well when the compositor runs at normal priority > > (lowest niceness or something like that for the commit work). > > I don't really like the naming convention approach.. what is to stop > some unrelated process to name it's thread the same thing to get a > SCHED_FIFO boost.. > > But we can stick with my idea to expose the thread id as a read-only > CRTC property, for userspace to find the things to call > sched_setscheduler() on. If for whatever reason the drm master is not > privileged (or is running in a sandbox, etc), a small helper that has > the necessary permissions could open the drm device to find the CRTC > thread-ids and call sched_setscheduler().. Hm thread ids don't translate too well across PID namespaces I think ... So that's another can of worms. And pidfd doesn't really work as a property. I also thought kernel threads can be distinguished from others, so userspace shouldn't be able to sneak in and get elevated by accident. -Daniel > > BR, > -R > > > -Daniel > > > > > Is there some way we could arrange for the per-crtc kthread's to be > > > owned by the drm master? That would solve the "must be root" issue. > > > And since the target audience is an atomic userspace, I suppose we > > > could expose the tid as a read-only property on the crtc? > > > > > > BR, > > > -R > > > > > > > So question to rt/worker folks: What's the best way to let userspace set > > > > the scheduling mode and priorities of things the kernel does on its > > > > behalf? Surely we're not the first ones where if userspace runs with some > > > > rt priority it'll starve out the kernel workers that it needs. Hardcoding > > > > something behind a subsystem ioctl (which just means every time userspace > > > > changes what it does, we need a new such flag or mode) can't be the right > > > > thing. > > > > > > > > Peter, Tejun? > > > > > > > > Thanks, Daniel > > > > > > > > > > > > > > Rob Clark (3): > > > > > drm/crtc: Introduce per-crtc kworker > > > > > drm/atomic: Use kthread worker for nonblocking commits > > > > > drm: Add a client-cap to set scheduling mode > > > > > > > > > > drivers/gpu/drm/drm_atomic_helper.c | 13 ++++++---- > > > > > drivers/gpu/drm/drm_auth.c | 4 ++++ > > > > > drivers/gpu/drm/drm_crtc.c | 37 +++++++++++++++++++++++++++++ > > > > > drivers/gpu/drm/drm_ioctl.c | 13 ++++++++++ > > > > > include/drm/drm_atomic.h | 31 ++++++++++++++++++++++++ > > > > > include/drm/drm_crtc.h | 10 ++++++++ > > > > > include/uapi/drm/drm.h | 13 ++++++++++ > > > > > 7 files changed, 117 insertions(+), 4 deletions(-) > > > > > > > > > > -- > > > > > 2.26.2 > > > > > > > > > > _______________________________________________ > > > > > dri-devel mailing list > > > > > dri-devel@lists.freedesktop.org > > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > > > -- > > > > Daniel Vetter > > > > Software Engineer, Intel Corporation > > > > http://blog.ffwll.ch > > > _______________________________________________ > > > dri-devel mailing list > > > dri-devel@lists.freedesktop.org > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch