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=-4.1 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 822DEC433DF for ; Tue, 21 Jul 2020 21:42:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B3552072E for ; Tue, 21 Jul 2020 21:42:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="vfHhkUH7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731283AbgGUVmm (ORCPT ); Tue, 21 Jul 2020 17:42:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731129AbgGUVmm (ORCPT ); Tue, 21 Jul 2020 17:42:42 -0400 Received: from mail-ej1-x643.google.com (mail-ej1-x643.google.com [IPv6:2a00:1450:4864:20::643]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F017AC0619DB; Tue, 21 Jul 2020 14:42:41 -0700 (PDT) Received: by mail-ej1-x643.google.com with SMTP id ga4so2864ejb.11; Tue, 21 Jul 2020 14:42:41 -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:content-transfer-encoding; bh=Dyi1MVLFGf/8/KPaE1swyyeNErOrv2bGUWjTcVj8gxM=; b=vfHhkUH7uUqVuea2i7a2v8nm3GlQGvrejsVXk1dY+oTV5cGgIufTlcUh4U03yDRrO3 3ZXPq4Kz7VxluI/vXrEjn4UOxXyeDw18jZS0yQLfsEyCCAiuGS09yjqLzQvJBo0gJjzD o9IFYUnweCqxm0XNV81CpeVFmCF1svsGMBkarpkK70EJKgJ1ohZtqMuFAyeMgNrM6j8L MY+Xde+v4jUiVgl27SGT20e/o7328q9sF+n94T5QfWFwKyoHltzu6agpEi5hm1pXHnph vAUoYRh2zp5yOEmbJdevHeUN0BLFZQLxBK1amF/HNbgoFB/AnU6n3ixeTu2aYpGx1bbJ scIw== 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:content-transfer-encoding; bh=Dyi1MVLFGf/8/KPaE1swyyeNErOrv2bGUWjTcVj8gxM=; b=ghvNLM8t/FBtnlEstWsHby1urjV87BTriviTS0HtSU9wXl9VIyLw1yrWpBzAKC7r+Y N4yPsp0o5nehC6h83hxMTE/E9pxOp+TF08/wJdDnE/R4b6Oci6PFlKCOETgNsJeoeIQi GxiJEZ1h1TJF9HtOF1rfji+UR/hy2J6zdkH+CKw/7b9py+Cg9Q0nHyDg2+SK4eOjfvHN 7EpOGlqheiywUmSgc44nPOSgggNdU1YiTIayNBkg2JoXSlwry2X9YVxVireu0W5ATBBW Ivc1OjRCt8QuEAJxd9bFHF6PIXwaobVlV8LYsC3mKjvgPXKTcWSQ64v1eVZiqCBvosIt vQww== X-Gm-Message-State: AOAM532Fa0YsQ1BJWSeMTIR8tmfhXto+j8CrP6KnxrIc1uvUMTMf1SUX yVWkSFnT3yqw4vsmDsz4OpH1CkdivxjnAyIO3u8= X-Google-Smtp-Source: ABdhPJwxE240DtGwFEuhHkKMPvfhlukuGNteVSI0paUJJOmdu+Jb46VZVXI0n2iDUJjFfIzHzYH2PLSYSUaSvNNdruQ= X-Received: by 2002:a17:906:f88a:: with SMTP id lg10mr26295104ejb.317.1595367760653; Tue, 21 Jul 2020 14:42:40 -0700 (PDT) MIME-Version: 1.0 References: <20200707201229.472834-4-daniel.vetter@ffwll.ch> <20200709123339.547390-1-daniel.vetter@ffwll.ch> <93b673b7-bb48-96eb-dc2c-bd4f9304000e@shipmail.org> <20200721074157.GB3278063@phenom.ffwll.local> <3603bb71-318b-eb53-0532-9daab62dce86@amd.com> <57a5eb9d-b74f-8ce4-7199-94e911d9b68b@shipmail.org> <2ca2c004-1e11-87f5-4bd8-761e1b44d21f@amd.com> <74727f17-b3a5-ca12-6db6-e47543797b72@shipmail.org> In-Reply-To: From: Dave Airlie Date: Wed, 22 Jul 2020 07:42:28 +1000 Message-ID: Subject: Re: [Linaro-mm-sig] [PATCH 1/2] dma-buf.rst: Document why indefinite fences are a bad idea To: =?UTF-8?Q?Christian_K=C3=B6nig?= Cc: =?UTF-8?Q?Thomas_Hellstr=C3=B6m_=28Intel=29?= , Daniel Vetter , Daniel Stone , linux-rdma , Intel Graphics Development , amd-gfx list , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Steve Pronovost , DRI Development , Jason Ekstrand , Jesse Natalie , Daniel Vetter , Thomas Hellstrom , Mika Kuoppala , Felix Kuehling , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org > > >> That's also why I'm not positive on the "no hw preemption, only > >> scheduler" case: You still have a dma_fence for the batch itself, > >> which means still no userspace controlled synchronization or other > >> form of indefinite batches allowed. So not getting us any closer to > >> enabling the compute use cases people want. > > What compute use case are you talking about? I'm only aware about the > wait before signal case from Vulkan, the page fault case and the KFD > preemption fence case. So slight aside, but it does appear as if Intel's Level 0 API exposes some of the same problems as vulkan. They have fences: "A fence cannot be shared across processes." They have events (userspace fences) like Vulkan but specify: "Signaled from the host, and waited upon from within a device=E2=80=99s com= mand list." "There are no protections against events causing deadlocks, such as circular waits scenarios. These problems are left to the application to avoid." https://spec.oneapi.com/level-zero/latest/core/PROG.html#synchronization-pr= imitives Dave.