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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E7478EA811C for ; Tue, 10 Feb 2026 14:11:16 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 323B710E59B; Tue, 10 Feb 2026 14:11:16 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.b="X6ZGNWCN"; dkim-atps=neutral Received: from mail-ej1-f74.google.com (mail-ej1-f74.google.com [209.85.218.74]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5332B10E595 for ; Tue, 10 Feb 2026 14:11:15 +0000 (UTC) Received: by mail-ej1-f74.google.com with SMTP id a640c23a62f3a-b88632ba0b5so621332166b.2 for ; Tue, 10 Feb 2026 06:11:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1770732674; x=1771337474; darn=lists.freedesktop.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=wpyZuzgNw/WGJaYO0aTw62Jp3X9Gu5cXyXe5IaYxcjU=; b=X6ZGNWCNrmbWlNPttgB5/zmDsquH+/8bikwgAuPGTZUW+ZglyDEhIllCqpN4QQlW6E f9LYJ5BeHAS4priZ2DAkJBYV+w0B2BRwssRycIfQy4ClG/ANNQkQX2P4+b5ScTy3CrQ7 reBBAthRxj3sRJnMEu8ZD/Ld/oLqoLO6468KBu4+ilzc6z8FqiRkgfYzTxSFaoGq/+l6 bVZkMlRx9bfQdZHOvb3PNAwwz411/zFaB3dMbRSmCvCOXeFPd2s68NIgugxWJdUWuXvD F05q5mKblrpQUigLEW4hNO7RinCnJRsxh6E1d7kviEUMtULIijdz4YzCW8FWdd2u/4AK A6lg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770732674; x=1771337474; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=wpyZuzgNw/WGJaYO0aTw62Jp3X9Gu5cXyXe5IaYxcjU=; b=LCTs0+T07ySp6D6CyZEeLcDWyfsuiyC7nks3iJdCAkv1jfN7StWtAUicQQ6tXhrqH5 Hw2uj0UxxTU6hem/sYRe0Pt607xnaO+D7EkEC62ld2hTGevC6WmPxRQrYB38o3HBFljh XOEQOiImN1VQR2YuruOYgxmZvawWD2FXWFMMZJdFkSLAFVquOnr0+71JAIBJGoWbuB5v wVM2xihpp/aNE1qqkGS6xfbs1PelhpyoXCneJCbFkJ/067lNMoQpbmfjM5Q7RB7iG5jq oF0/zkz7yNMmshZ+XG7aWHFYmkPVnvdwvAmNhQ+o7tpAM0Oc7wKYldYR4yZ9p8qZOcLz mHsg== X-Forwarded-Encrypted: i=1; AJvYcCVi4eCGqDK2+r1AXnLdoeoGoMd9QaFGNV9uNW0cpgwkwj0t7sjTSGkM1Iw9HRnua4/OvQiUIGi262U=@lists.freedesktop.org X-Gm-Message-State: AOJu0YymcMk5JcgbiSlfsZ/bc+6Ta4B5Sf9KYWUzaqnGr3u5xoZz9MMp IYTdvfJsquOPxWjP5hSNCcTx2YfSZ8JIokscn0757GubqBmvWcOS6J3RDnAm6oR1rH/pq4s0vXZ YPIimQSJnLuV+EOpOLQ== X-Received: from ejca6.prod.google.com ([2002:a17:906:3686:b0:b8e:7d43:b280]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a17:906:f58b:b0:b86:f194:9eec with SMTP id a640c23a62f3a-b8edf1ea493mr956084166b.18.1770732673626; Tue, 10 Feb 2026 06:11:13 -0800 (PST) Date: Tue, 10 Feb 2026 14:11:12 +0000 In-Reply-To: <20260210145156.108ab292@fedora> Mime-Version: 1.0 References: <20260209155843.725dcfe1@fedora> <20260210101525.7fb85f25@fedora> <20260210134913.33cb674f@fedora> <20260210145156.108ab292@fedora> Message-ID: Subject: Re: [RFC PATCH 2/4] rust: sync: Add dma_fence abstractions From: Alice Ryhl To: Boris Brezillon Cc: "Christian =?utf-8?B?S8O2bmln?=" , Philipp Stanner , phasta@kernel.org, Danilo Krummrich , David Airlie , Simona Vetter , Gary Guo , Benno Lossin , Daniel Almeida , Joel Fernandes , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, Feb 10, 2026 at 02:51:56PM +0100, Boris Brezillon wrote: > On Tue, 10 Feb 2026 13:26:48 +0000 > Alice Ryhl wrote: > > > On Tue, Feb 10, 2026 at 01:49:13PM +0100, Boris Brezillon wrote: > > > On Tue, 10 Feb 2026 10:15:04 +0000 > > > Alice Ryhl wrote: > > > > > > > /// The owner of this value must ensure that this fence is signalled. > > > > struct MustBeSignalled<'fence> { ... } > > > > /// Proof value indicating that the fence has either already been > > > > /// signalled, or it will be. The lifetime ensures that you cannot mix > > > > /// up the proof value. > > > > struct WillBeSignalled<'fence> { ... } > > > > > > Sorry, I have more questions, unfortunately. Seems that > > > {Must,Will}BeSignalled are targeting specific fences (at least that's > > > what the doc and 'fence lifetime says), but in practice, the WorkItem > > > backing the scheduler can queue 0-N jobs (0 if no jobs have their deps > > > met, and N > 1 if more than one job is ready). Similarly, an IRQ > > > handler can signal 0-N fences (can be that the IRQ has nothing to do we > > > job completion, or, it can be that multiple jobs have completed). How > > > is this MustBeSignalled object going to be instantiated in practice if > > > it's done before the DmaFenceWorkItem::run() function is called? > > > > The {Must,Will}BeSignalled closure pair needs to wrap the piece of code > > that ensures a specific fence is signalled. If you have code that > > manages a collection of fences and invokes code for specific fences > > depending on outside conditions, then that's a different matter. > > > > After all, transfer_to_wq() has two components: > > 1. Logic to ensure any spawned workqueue job eventually gets to run. > > 2. Once the individual job runs, logic specific to the one fence ensures > > that this one fence gets signalled. > > Okay, that's a change compared to how things are modeled in C (and in > JobQueue) at the moment: the WorkItem is not embedded in a specific > job, it's something that's attached to the JobQueue. The idea being > that the WorkItem represents a task to be done on the queue itself > (check if the first element in the queue is ready for execution), not on > a particular job. Now, we could change that and have a per-job WorkItem, > but ultimately, we'll have to make sure jobs are dequeued in order > (deps on JobN can be met before deps on Job0, but we still want JobN to > be submitted after Job0), and we'd pay the WorkItem overhead once per > Job instead of once per JobQueue. Probably not the end of the world, > but it's worth considering, still. It sounds like the fix here is to have transfer_to_job_queue() instead of trying to do it at the workqueue level. > > And {Must,Will}BeSignalled exists to help model part (2.). But what you > > described with the IRQ callback falls into (1.) instead, which is > > outside the scope of {Must,Will}BeSignalled (or at least requires more > > complex APIs). > > For IRQ callbacks, it's not just about making sure they run, but also > making sure nothing in there can lead to deadlocks, which is basically > #2, except it's not scoped to a particular fence. It's just a "fences > can be signaled from there" marker. We could restrict it to "fences of > this particular implementation can be signaled from there" but not > "this particular fence instance will be signaled next, if any", because > that we don't know until we've walked some HW state to figure out which > job is complete and thus which fence we need to signal (the interrupt > we get is most likely multiplexing completion on multiple GPU contexts, > so before we can even get to our per-context in-flight-jobs FIFO, we > need to demux this thing). All I can say is that this is a different use-case for the C api dma_fence_begin_signalling(). This different usage also seems useful, but it would be one that does not involve {Must,Will}BeSignalled arguments at all. After all, dma_fence_begin_signalling() only requires those arguments if you want to convert a PrivateFence into a PublishedFence. (I guess a better name is PublishableFence.) If you're not trying to prove that a specific fence will be signalled, then you don't need the {Must,Will}BeSignalled arguments. Alice