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 77F2AC4363D for ; Thu, 24 Sep 2020 02:33:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1CFB1221EB for ; Thu, 24 Sep 2020 02:33:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Sb9qryrR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726281AbgIXCdb (ORCPT ); Wed, 23 Sep 2020 22:33:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726196AbgIXCdb (ORCPT ); Wed, 23 Sep 2020 22:33:31 -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 DD046C0613CE; Wed, 23 Sep 2020 19:33:30 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id e11so5760440wme.0; Wed, 23 Sep 2020 19:33:30 -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 :cc; bh=HIIzE4x42RNMtao8I/EFJNqIpjg/pv4TDKmeWW312yg=; b=Sb9qryrRT855vnKQoiFjZufBig+mgkhfXyIiuOhXvrFcJOBTfwyYaJUPmRuowuyV3V LX1aphnvpIDF6W5cB645nEJx35rAxn3tKxJ+Aju2JH5LZ0SgEfidyapdkU4xx5L7zND+ ZA9KrHE70xY9rOFHiZ3BN3UCrNHvEn1JyZOmx56yJpiYgdXtMSp75DJqf483jCC94yBT SZLtY2bc0rF3VjHdmBaR+l8/NOt174nDkL9laVTx0jL1fkyubfpL+koRC29yQoGNf3kM bphjnAjN435GXWzw0KQQ1Cvk9pR67KUToI0lPwfI5ZPGqR7DzLbWDD601uggR0+W5+RQ +LPw== 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:cc; bh=HIIzE4x42RNMtao8I/EFJNqIpjg/pv4TDKmeWW312yg=; b=VwL7S02yxgVsvW2ScqqbbqF4j/PpG6OUAZkyol0ZsR7Ua5U83QXBajvHQm06QDWZv4 RKwHwavAGappdNXXyylsQDozGSOzwvMKz1DHnFlM5qCFx7W1nz4J4nKOjKPsmIESpQvr knTXspfJ6OZw2EHoI7WLZDZt8s+O/c6D+sfqGcD4Ara/GgGvgoYJAj7r7nTPxUWRTBCa CvcA3B5lc0w7O5JZOGB4qu1CxeiDHWwJBSucLjC+Jjz7UfEJiHMqgMF75Me8IHocIwfN IDBzy5j4RLR7YzfKn6JoPvBgEcfuq8KRFWZvRhwq6T9aRAXuu78sUrT78HXMZWWsQTVQ l6hA== X-Gm-Message-State: AOAM532gPH8wHXayAkk+8Xg7V2NwW+yzknlFQvd6NLziLJubrB21gbpF 3nNUhhDNPDJct9jAGXazzYgf4Hr4mr1CFb1P1K4= X-Google-Smtp-Source: ABdhPJw+2kZ2XPtA/jFmdSyqH3JXHfNLkj/gvnXEchdgkwiEqJDw25Yy+mHM9uIFFkPngwwyq4VPJhRERxlm8am962I= X-Received: by 2002:a7b:cf1a:: with SMTP id l26mr2193637wmg.164.1600914809415; Wed, 23 Sep 2020 19:33:29 -0700 (PDT) MIME-Version: 1.0 References: <20200919193727.2093945-1-robdclark@gmail.com> <20200921092154.GJ438822@phenom.ffwll.local> <20200923152545.GQ438822@phenom.ffwll.local> In-Reply-To: <20200923152545.GQ438822@phenom.ffwll.local> From: Rob Clark Date: Wed, 23 Sep 2020 19:33:17 -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 Cc: Daniel Vetter Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Wed, Sep 23, 2020 at 8:25 AM Daniel Vetter wrote: > > 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. hmm, I was kinda hoping there was already a solution for translating thread-id's, but hadn't had a chance to dig through it yet > I also thought kernel threads can be distinguished from others, so > userspace shouldn't be able to sneak in and get elevated by accident. I guess maybe you could look at the parent? I still would like to think that we could come up with something a bit less shaking than matching thread names by regexp.. BR, -R > -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 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 4654BC2D0A8 for ; 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Wed, 23 Sep 2020 19:33:29 -0700 (PDT) MIME-Version: 1.0 References: <20200919193727.2093945-1-robdclark@gmail.com> <20200921092154.GJ438822@phenom.ffwll.local> <20200923152545.GQ438822@phenom.ffwll.local> In-Reply-To: <20200923152545.GQ438822@phenom.ffwll.local> From: Rob Clark Date: Wed, 23 Sep 2020 19:33:17 -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 Wed, Sep 23, 2020 at 8:25 AM Daniel Vetter wrote: > > 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. hmm, I was kinda hoping there was already a solution for translating thread-id's, but hadn't had a chance to dig through it yet > I also thought kernel threads can be distinguished from others, so > userspace shouldn't be able to sneak in and get elevated by accident. I guess maybe you could look at the parent? I still would like to think that we could come up with something a bit less shaking than matching thread names by regexp.. BR, -R > -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 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel