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=-7.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 33672C433E7 for ; Mon, 31 Aug 2020 15:09:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0AA0520866 for ; Mon, 31 Aug 2020 15:09:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="YR54dxRc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728190AbgHaPJI (ORCPT ); Mon, 31 Aug 2020 11:09:08 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:42900 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728129AbgHaPJH (ORCPT ); Mon, 31 Aug 2020 11:09:07 -0400 Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id E1436277; Mon, 31 Aug 2020 17:09:02 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1598886543; bh=9LeMEkjHn/mN7lSe6JBUC4vihKLkljIJ6v1PdNeA2vw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YR54dxRc6PBodNkt2MxTDyLzGD2VgzAkw5EXaRwKKitko0XrzaQO5eR/WWnMyCE6a x/LOyhqHzXb+YT0n0bZY8iVDNYdHGbjHk9oCa4VrPUzMhusBaM4oEd8G/m/Jhv/kQX fvpLJdBFwawmBkiWLZkINvasStlGvuquTfmK5OxQ= Date: Mon, 31 Aug 2020 18:08:41 +0300 From: Laurent Pinchart To: James Jones Cc: Ezequiel Garcia , Brian Starkey , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, Sumit Semwal , "Andrew F . Davis" , Benjamin Gaignard , Liam Mark , Laura Abbott , John Stultz , Daniel Stone , Nicolas Dufresne , Robert Beckett , Tomasz Figa , kernel@collabora.com, nd@arm.com Subject: Re: [RFC] Experimental DMA-BUF Device Heaps Message-ID: <20200831150841.GK16155@pendragon.ideasonboard.com> References: <20200816172246.69146-1-ezequiel@collabora.com> <20200817151813.wet5faqg4fzlfbsh@DESKTOP-E1NTVVP.localdomain> <746a0bb75bd8388a30b53a5ddc56fb24aea308a8.camel@collabora.com> <4f987e06-7af1-671b-836a-10d3e9623547@nvidia.com> <20200823204637.GF6002@pendragon.ideasonboard.com> <5a03e7d8-15cf-1323-31c1-74ae78f4f9c6@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5a03e7d8-15cf-1323-31c1-74ae78f4f9c6@nvidia.com> Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi James, On Sun, Aug 23, 2020 at 03:53:50PM -0700, James Jones wrote: > On 8/23/20 1:46 PM, Laurent Pinchart wrote: > > On Sun, Aug 23, 2020 at 01:04:43PM -0700, James Jones wrote: > >> On 8/20/20 1:15 AM, Ezequiel Garcia wrote: > >>> On Mon, 2020-08-17 at 20:49 -0700, James Jones wrote: > >>>> On 8/17/20 8:18 AM, Brian Starkey wrote: > >>>>> On Sun, Aug 16, 2020 at 02:22:46PM -0300, Ezequiel Garcia wrote: > >>>>>> This heap is basically a wrapper around DMA-API dma_alloc_attrs, > >>>>>> which will allocate memory suitable for the given device. > >>>>>> > >>>>>> The implementation is mostly a port of the Contiguous Videobuf2 > >>>>>> memory allocator (see videobuf2/videobuf2-dma-contig.c) > >>>>>> over to the DMA-BUF Heap interface. > >>>>>> > >>>>>> The intention of this allocator is to provide applications > >>>>>> with a more system-agnostic API: the only thing the application > >>>>>> needs to know is which device to get the buffer for. > >>>>>> > >>>>>> Whether the buffer is backed by CMA, IOMMU or a DMA Pool > >>>>>> is unknown to the application. > >>>>>> > >>>>>> I'm not really expecting this patch to be correct or even > >>>>>> a good idea, but just submitting it to start a discussion on DMA-BUF > >>>>>> heap discovery and negotiation. > >>>>>> > >>>>> > >>>>> My initial reaction is that I thought dmabuf heaps are meant for use > >>>>> to allocate buffers for sharing across devices, which doesn't fit very > >>>>> well with having per-device heaps. > >>>>> > >>>>> For single-device allocations, would using the buffer allocation > >>>>> functionality of that device's native API be better in most > >>>>> cases? (Some other possibly relevant discussion at [1]) > >>>>> > >>>>> I can see that this can save some boilerplate for devices that want > >>>>> to expose private chunks of memory, but might it also lead to 100 > >>>>> aliases for the system's generic coherent memory pool? > >>>>> > >>>>> I wonder if a set of helpers to allow devices to expose whatever they > >>>>> want with minimal effort would be better. > >>>> > >>>> I'm rather interested on where this goes, as I was toying with using > >>>> some sort of heap ID as a basis for a "device-local" constraint in the > >>>> memory constraints proposals Simon and I will be discussing at XDC this > >>>> year. It would be rather elegant if there was one type of heap ID used > >>>> universally throughout the kernel that could provide a unique handle for > >>>> the shared system memory heap(s), as well as accelerator-local heaps on > >>>> fancy NICs, GPUs, NN accelerators, capture devices, etc. so apps could > >>>> negotiate a location among themselves. This patch seems to be a step > >>>> towards that in a way, but I agree it would be counterproductive if a > >>>> bunch of devices that were using the same underlying system memory ended > >>>> up each getting their own heap ID just because they used some SW > >>>> framework that worked that way. > >>>> > >>>> Would appreciate it if you could send along a pointer to your BoF if it > >>>> happens! > >>> > >>> Here is it: > >>> > >>> https://linuxplumbersconf.org/event/7/contributions/818/ > >>> > >>> It would be great to see you there and discuss this, > >>> given I was hoping we could talk about how to meet a > >>> userspace allocator library expectations as well. > >> > >> Thanks! I hadn't registered for LPC and it looks like it's sold out, > >> but I'll try to watch the live stream. > >> > >> This is very interesting, in that it looks like we're both trying to > >> solve roughly the same set of problems but approaching it from different > >> angles. From what I gather, your approach is that a "heap" encompasses > >> all the allocation constraints a device may have. > >> > >> The approach Simon Ser and I are tossing around so far is somewhat > >> different, but may potentially leverage dma-buf heaps a bit as well. > >> > >> Our approach looks more like what I described at XDC a few years ago, > >> where memory constraints for a given device's usage of an image are > >> exposed up to applications, which can then somehow perform boolean > >> intersection/union operations on them to arrive at a common set of > >> constraints that describe something compatible with all the devices & > >> usages desired (or fail to do so, and fall back to copying things around > >> presumably). I believe this is more flexible than your initial proposal > >> in that devices often support multiple usages (E.g., different formats, > >> different proprietary layouts represented by format modifiers, etc.), > >> and it avoids adding a combinatorial number of heaps to manage that. > >> > >> In my view, heaps are more like blobs of memory that can be allocated > >> from in various different ways to satisfy constraints. I realize heaps > >> mean something specific in the dma-buf heap design (specifically, > >> something closer to an association between an "allocation mechanism" and > >> "physical memory"), but I hope we don't have massive heap/allocator > >> mechanism proliferation due to constraints alone. Perhaps some > >> constraints, such as contiguous memory or device-local memory, are > >> properly expressed as a specific heap, but consider the proliferation > >> implied by even that simple pair of examples: How do you express > >> contiguous device-local memory? Do you need to spawn two heaps on the > >> underlying device-local memory, one for contiguous allocations and one > >> for non-contiguous allocations? Seems excessive. > >> > >> Of course, our approach also has downsides and is still being worked on. > >> For example, it works best in an ideal world where all the allocators > >> available understand all the constraints that exist. > > > > Shouldn't allocators be decoupled of constraints ? In my imagination I > > see devices exposing constraints, and allocators exposing parameters, > > with a userspace library to reconcile the constraints and produce > > allocator parameters from them. > > Perhaps another level of abstraction would help. I'll have to think > about that. > > However, as far as I can tell, it wouldn't remove the need to > communicate a lot of constraints from multiple engines/devices/etc. to > the allocator (likely a single allocator. I'd be interested to know if > anyone has a design that effectively uses multiple allocators to satisfy > a single allocation request, but I haven't come up with a good one) > somehow. Either the constraints are directly used as the parameters, or > there's a translation/second level of abstraction, but either way much > of the information needs to make it to the allocator, or represent the > need to use a particular allocator. Simple things like pitch and offset > alignment can be done without help from a kernel-level allocator, but > others such as cache coherency, physical memory bank placement, or > device-local memory will need to make it all the way down to the kernel > some how I believe. I fully agree that we'll need kernel support, but I don't think the constraints reporting API and the allocator API need to speak the same language. For instance, drivers will report alignment constraints, the userspace allocator library will translate that to a pitch value, and pass it to the allocator as an allocation parameter. The allocator won't know about alignment constraints. That's a simple example, let's see how it turns out with more complex constraints. With a centralized userspace library we have the ability to decouple the two sides, which I believe can be useful to keep the complexity of constraints and allocation parameters (as) low (as possible). > >> Dealing with a > >> reality where there are probably a handful of allocators, another > >> handful of userspace libraries and APIs, and still more applications > >> trying to make use of all this is one of the larger remaining challenges > >> of the design. > >> > >> We'll present our work at XDC 2020. Hope you can check that out as well! > >> > >>>>> 1. https://lore.kernel.org/dri-devel/57062477-30e7-a3de-6723-a50d03a402c4@kapsi.fi/ > >>>>> > >>>>>> Given Plumbers is just a couple weeks from now, I've submitted > >>>>>> a BoF proposal to discuss this, as perhaps it would make > >>>>>> sense to discuss this live? > >>>>>> > >>>>>> Not-signed-off-by: Ezequiel Garcia > > -- Regards, Laurent Pinchart