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 CE7DFE9E2FA for ; Wed, 11 Feb 2026 12:22:08 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2130610E0A0; Wed, 11 Feb 2026 12:22:08 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.b="1O01DKWm"; dkim-atps=neutral Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) by gabe.freedesktop.org (Postfix) with ESMTPS id 47F3010E0A0 for ; Wed, 11 Feb 2026 12:22:06 +0000 (UTC) Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-483129eb5ccso27702355e9.2 for ; Wed, 11 Feb 2026 04:22:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1770812525; x=1771417325; darn=lists.freedesktop.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=ux5jpTmdkj1HTNBhdFzkT0KL7QZx+1iaLGF6Z9eCsjc=; b=1O01DKWm5KomoCG2Mg7xh+FtVPjNBOlddbt+lvjMBfe3EPB1/u8OCWZ9pDrkM/NCZd aG6wS8iusGRVaA9XyTePiOaLqTjnQsryxtcbFalhbhfzqVU0CYrecEF5NwEZqCuLDZBU LxpL/U7045TwpiPSy3/4mHvM1JGbfewotb8oKLYKYylZBl57QKBnUnPCXm5aK6L17Gdy kDrTkiSeIWoQ1l4ZAbVxkwewioCmFjWinHiingARBDnFlIXPhGraJ1NXoR1UzI0USDFk EzSn5CK4FXtX1nZuSvAlx5Tnu74se4uoYMYdnoI5XTk/P79RgLTeIc8BiLIqJiuuvGis zY/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770812525; x=1771417325; h=content-transfer-encoding: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=ux5jpTmdkj1HTNBhdFzkT0KL7QZx+1iaLGF6Z9eCsjc=; b=rM74y+0Bwg+LQOnuWwG/Mgf5aIoGu1hiKwwfJLZehUl/oDyJocVneSO92RT4eCjbw6 Cw/CsWrolkingZoQ7F1eNsFFRukBxncV/ipJbqo+e0/b9BFg/I2i3FRKvmmX43SLlq9J 2lBP6NcU3ghumbIbLjdyLuPvNww5y8kkR2/yLH6iNsXv8snKJVyLvWVuHeBvhsxp5Tfw xwUCLeU3aBmX/9cxbCRthz+bWaKMB6p1ldhpijFCYTo24uxOD45Ga55BshRxv5g3cIhU 8dTHd5dTXWCyX3CfrYvtL8xS0+iACHEyYDWhf91Ge8yaXsTYhEs6tZ0DMMQ3MtmDUFAl 6kpg== X-Forwarded-Encrypted: i=1; AJvYcCWKkzaev9LPOzCrxdSueBG2cpMTU2VmE+c+Xnjj/PPi9cGzZ6VXeiqJiv9J5hOW2Gy7G2tsuy6Mwcw=@lists.freedesktop.org X-Gm-Message-State: AOJu0Yw0LXYfNHUXyb7KpQxJMqAli1k8Wfp3y+AY2lfpBhpVq0OJren8 Z7tg0N4jV0LYevR0aYok9nqI5ywvPRlNe3tYwf4HNsiBQwUPltRX8Efzwwd8syr/5VE4hsp/CAG onmm37cNZ8fEb5sTw4A== X-Received: from wmbe3.prod.google.com ([2002:a05:600c:5903:b0:480:694a:dd63]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:19c7:b0:477:9814:6882 with SMTP id 5b1f17b1804b1-483201dd0afmr240550065e9.5.1770812524805; Wed, 11 Feb 2026 04:22:04 -0800 (PST) Date: Wed, 11 Feb 2026 12:22:03 +0000 In-Reply-To: Mime-Version: 1.0 References: <20260203081403.68733-2-phasta@kernel.org> <20260203081403.68733-5-phasta@kernel.org> <20260210155750.5cdbe6cc@fedora> <8ea48ce49f2c7b6fd715dd54c24e755e8ac3262c.camel@mailbox.org> <20260211120742.0e9e7122@fedora> Message-ID: Subject: Re: [RFC PATCH 3/4] rust/drm: Add DRM Jobqueue From: Alice Ryhl To: phasta@kernel.org Cc: Boris Brezillon , David Airlie , Simona Vetter , Danilo Krummrich , Gary Guo , Benno Lossin , "Christian =?utf-8?B?S8O2bmln?=" , 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" Content-Transfer-Encoding: quoted-printable 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 Wed, Feb 11, 2026 at 12:19:56PM +0100, Philipp Stanner wrote: > On Wed, 2026-02-11 at 12:07 +0100, Boris Brezillon wrote: > > On Wed, 11 Feb 2026 11:47:27 +0100 > > Philipp Stanner wrote: > >=20 > > > On Tue, 2026-02-10 at 15:57 +0100, Boris Brezillon wrote: > > > > On Tue,=C2=A0 3 Feb 2026 09:14:02 +0100 > > > > Philipp Stanner wrote: > > > > =C2=A0=20 > > > > > +/// A jobqueue Job. > > > > > +/// > > > > > +/// You can stuff your data in it. The job will be borrowed back= to your driver > > > > > +/// once the time has come to run it. > > > > > +/// > > > > > +/// Jobs are consumed by [`Jobqueue::submit_job`] by value (owne= rship transfer). > > > > > +/// You can set multiple [`DmaFence`] as dependencies for a job.= It will only > > > > > +/// get run once all dependency fences have been signaled. > > > > > +/// > > > > > +/// Jobs cost credits. Jobs will only be run if there are is eno= ugh capacity in > > > > > +/// the jobqueue for the job's credits. It is legal to specify j= obs costing 0 > > > > > +/// credits, effectively disabling that mechanism. > > > > > +#[pin_data] > > > > > +pub struct Job { > > > > > +=C2=A0=C2=A0=C2=A0 cost: u32, > > > > > +=C2=A0=C2=A0=C2=A0 #[pin] > > > > > +=C2=A0=C2=A0=C2=A0 pub data: T, > > > > > +=C2=A0=C2=A0=C2=A0 done_fence: Option>>, > > > > > +=C2=A0=C2=A0=C2=A0 hardware_fence: Option>>, > > > > > +=C2=A0=C2=A0=C2=A0 nr_of_deps: AtomicU32, > > > > > +=C2=A0=C2=A0=C2=A0 dependencies: List,=C2=A0=20 > > > >=20 > > > > Given how tricky Lists are in rust, I'd recommend going for an XArr= ay, > > > > like we have on the C side. There's a bit of overhead when the job = only > > > > has a few deps, but I think simplicity beats memory-usage-optimizat= ions > > > > in that case (especially since the overhead exists and is accepted = in > > > > C).=C2=A0=20 > > >=20 > > > I mean, the list is now already implemented and works. Considering th= e > > > XArray would have made sense during the development difficulties. > >=20 > > I'm sure it does, but that's still more code/tricks to maintain than > > what you'd have with the XArray abstraction. >=20 > The solution than will rather be to make the linked list implementation > better. >=20 > A list is the correct data structure in a huge number of use cases in > the kernel. We should not begin here to defer to other structures > because of convenience. Rust vs C aside, linked lists are often used in the kernel despite not being the best choice. They are extremely cache unfriendly and inefficient; most of the time a vector or xarray is far faster if you can accept an ENOMEM failure path when adding elements. I have heard several times from C maintainers that overuse of list is making the kernel slow in a death from a thousand cuts situation. This applies to the red/black tree too, by the way. Alice