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=-3.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 17C39C43465 for ; Mon, 21 Sep 2020 16:19:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE6BD2076B for ; Mon, 21 Sep 2020 16:19:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KfkhuXyn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727070AbgIUQTp (ORCPT ); Mon, 21 Sep 2020 12:19:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728029AbgIUQTo (ORCPT ); Mon, 21 Sep 2020 12:19:44 -0400 Received: from mail-wm1-x341.google.com (mail-wm1-x341.google.com [IPv6:2a00:1450:4864:20::341]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57284C061755; Mon, 21 Sep 2020 09:19:44 -0700 (PDT) Received: by mail-wm1-x341.google.com with SMTP id l9so91595wme.3; Mon, 21 Sep 2020 09:19:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=frI/81YNEfF9ORgJP4cNFL/lMzPALXCIhz8JBfMDSJ4=; b=KfkhuXyn0MBCPpYJk6pycw90nfN0ATte7JpEFc6pVifh+hcn4Lg3PZXaAfQYwQ3Zvj HRQr5zsxuJdE7l8FtwiTVxv+5QYxYtL3CRSH4NDcjxxOOWvyTKGLxQ94a2p6dR73k8Wi pozDiRM93qhoDZZXUaMSfE/7G+QF+J5c2DAGXAy4u5s1LHU0PfHkjfzonr9+WAiiuL1a Y13C6RNgR7S4DmelSt27yuDLXpJnfmN8dhk9HygCYduPxVechRe2FmjBAFkh6N61dXJm EVqkk65zAl8qVCS4z6ZnaBRcjPXmHvsC5tEKe2bb619/GidC/WsXcmZXhZZiWp1GEfut FDPQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=frI/81YNEfF9ORgJP4cNFL/lMzPALXCIhz8JBfMDSJ4=; b=m7947b2i8Puj+MCIqE3VX2i5AtmxFnt/yugcVBm6o7yA5KaM1GEyBhCbEgTHXqR8aF XpLO8M5+pkNYeTXGYMcwhpqGzrJTT+wF7HQnlkpiEY3Lu+HC8tMOLU97qKSb/8T3ebrE k0WxQZStEk62w7ocNAkQjN18RT0LFGySzPEKbPJDK2m5vi20hMV52XzUHjNfiCfVfnwP idiQoEC+qbD4JNms+lQuYw3bBnD/GBHoEuADlGSjjkhD+pXr6qzuZeJihCTNcYLLHoqt Uek7ahD1Jiqs3QfuTHQPLBMbZHSNQCNOpSGuJ5Rd/SAiXg3ioKu5s9+jVBKlPmtMe3FC Wu1Q== X-Gm-Message-State: AOAM533hBhOPAb9Go+XVYm4p19NNouN4bpwNql5Fxjx1M3zAe3DDGS+V nl0gQKlGWEJ/Y3KVZ+05CoMzmHr7sHe1kzbaZuQ= X-Google-Smtp-Source: ABdhPJxf9lfDqxY8F+FK4AKpLfdsEvfGPLfQpr97E0XD7LNO/i9dSvLCc8SRa733kjhb9MUhJfsUonQQyw8yiTGu5j0= X-Received: by 2002:a05:600c:2183:: with SMTP id e3mr156635wme.49.1600705182905; Mon, 21 Sep 2020 09:19:42 -0700 (PDT) MIME-Version: 1.0 References: <20200919193727.2093945-1-robdclark@gmail.com> <20200921092154.GJ438822@phenom.ffwll.local> In-Reply-To: From: Rob Clark Date: Mon, 21 Sep 2020 09:19:31 -0700 Message-ID: Subject: Re: [PATCH 0/3] drm: commit_work scheduling To: Rob Clark , dri-devel , Rob Clark , Peter Zijlstra , linux-arm-msm , open list , Tim Murray , Tejun Heo Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Mon, Sep 21, 2020 at 8:16 AM 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. > > 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? Looks like kthread goes out of it's way to *not* be owned by users (to avoid fork, and such complications?) But maybe we could modify the kthread_worker's task->real_cred? I didn't see any examples of anything else doing something similar, so I'm not sure what sorts of dragons there lie.. > 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 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=-3.3 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 B2BCFC43468 for ; 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Mon, 21 Sep 2020 09:19:42 -0700 (PDT) MIME-Version: 1.0 References: <20200919193727.2093945-1-robdclark@gmail.com> <20200921092154.GJ438822@phenom.ffwll.local> In-Reply-To: From: Rob Clark Date: Mon, 21 Sep 2020 09:19:31 -0700 Message-ID: Subject: Re: [PATCH 0/3] drm: commit_work scheduling To: Rob Clark , dri-devel , Rob Clark , Peter Zijlstra , linux-arm-msm , open list , Tim Murray , Tejun Heo X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Mon, Sep 21, 2020 at 8:16 AM 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. > > 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? Looks like kthread goes out of it's way to *not* be owned by users (to avoid fork, and such complications?) But maybe we could modify the kthread_worker's task->real_cred? I didn't see any examples of anything else doing something similar, so I'm not sure what sorts of dragons there lie.. > 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