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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 46EBDC433E0 for ; Wed, 1 Jul 2020 17:15:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 198D7206BE for ; Wed, 1 Jul 2020 17:15:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="iMvRepgl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729465AbgGARP1 (ORCPT ); Wed, 1 Jul 2020 13:15:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48612 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729328AbgGARP1 (ORCPT ); Wed, 1 Jul 2020 13:15:27 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 04E2AC08C5C1 for ; Wed, 1 Jul 2020 10:15:27 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id r12so14503530ilh.4 for ; Wed, 01 Jul 2020 10:15:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=XxnIxtjRpDkvkw51GDJVMxPTPGtFOykolSOKsxdLZrI=; b=iMvRepgl7G2zNXZ76Hr/JM0kvklKj2OppBxjxki23srGIrq6ioLxbixoQwwF7o1gQ3 mc8DiDRPkO9ZyXHbNZ0Jh4v2uQwXQA2gROyeb/mgI4mJFKsKttQ9NEbiEMzptwBUStYL 2W8vWBjzv+7LD4ciLeUZbm8WPBdaSb/yTwUFHpFfhvlOPA8eFvPChumv6qX/xUZWJaS7 WExrJXqm1XpHR8IWSlASm6a0MgLkfL0lsNNB5/u0oF0nfUb5jMsYAMMqMDqNPbWIUoUy CDrBg1oCeaG5p8JYa2fTsFbABglV5FY6TMeSOyvHrYsOn6LQ9x16PZAKJJggXGpO9L2h Bmyw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=XxnIxtjRpDkvkw51GDJVMxPTPGtFOykolSOKsxdLZrI=; b=pOb0eZt1yPriJtxLM2oeSrKp3aiPg0o4RmRTgXH/IfQl61DHHpHDEghXoc+8lVXjgu vwMyDjbv2LSao3tjPgOPAGiUX4AhHHw1w/BbxhCNYJzsQW3KhwZkFgpU0HBrumDy3vCR v7cLwuQF/5kcm7/E+3AyYfyLE4a343YJouAo7oKtR+rK6Tf9UUSHhpqDhprB1rmwDxzO KJwn6OyFxgUXyGpo6vBweCrJaSZPM/OaSELjHod0dWXEtL52bGcmxAxSWQz1OsHxILmX E2yuvcQ4F559ReZXqXrTPLKeEUMEch7qrLAQc5nUOFWmHeZhdSXXeiKQmtGlHKwOkdG1 6G1g== X-Gm-Message-State: AOAM531Gn3f4QLVVkz1cFBnLnLCsi7xWM84UyaqGWVRIQo15KnB+5fTC kjDfyBKFAfhSJFuTi8/6EnQCQA== X-Google-Smtp-Source: ABdhPJxhHTHmbob6OQdYcormvVS6B2LDFca749np99vHRxmGD/Dd5URAcW/wKfoHCWMGpgIuDlfENA== X-Received: by 2002:a92:844b:: with SMTP id l72mr9137016ild.19.1593623725989; Wed, 01 Jul 2020 10:15:25 -0700 (PDT) Received: from ziepe.ca ([206.223.160.26]) by smtp.gmail.com with ESMTPSA id t6sm3162260ioi.20.2020.07.01.10.15.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 10:15:25 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.93) (envelope-from ) id 1jqgKS-002ans-8p; Wed, 01 Jul 2020 14:15:24 -0300 Date: Wed, 1 Jul 2020 14:15:24 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: Christian =?utf-8?B?S8O2bmln?= , Leon Romanovsky , "linux-rdma@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Doug Ledford , "Vetter, Daniel" , "Xiong, Jianxin" Subject: Re: [RFC PATCH v2 0/3] RDMA: add dma-buf support Message-ID: <20200701171524.GN25301@ziepe.ca> References: <1593451903-30959-1-git-send-email-jianxin.xiong@intel.com> <20200629185152.GD25301@ziepe.ca> <20200630173435.GK25301@ziepe.ca> <9b4fa0c2-1661-6011-c552-e37b05f35938@amd.com> <20200701123904.GM25301@ziepe.ca> <34077a9f-7924-fbb3-04d9-cd20243f815c@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Wed, Jul 01, 2020 at 05:42:21PM +0200, Daniel Vetter wrote: > > >> All you need is the ability to stop wait for ongoing accesses to end and > > >> make sure that new ones grab a new mapping. > > > Swap and flush isn't a general HW ability either.. > > > > > > I'm unclear how this could be useful, it is guarenteed to corrupt > > > in-progress writes? > > > > > > Did you mean pause, swap and resume? That's ODP. > > > > Yes, something like this. And good to know, never heard of ODP. > > Hm I thought ODP was full hw page faults at an individual page > level, Yes > and this stop&resume is for the entire nic. Under the hood both apply > back-pressure on the network if a transmission can't be received, > but NIC's don't do stop and resume, blocking the Rx pipe is very problematic and performance destroying. The strategy for something like ODP is more complex, and so far no NIC has deployed it at any granularity larger than per-page. > So since Jason really doesn't like dma_fence much I think for rdma > synchronous it is. And it shouldn't really matter, since waiting for a > small transaction to complete at rdma wire speed isn't really that > long an operation. Even if DMA fence were to somehow be involved, how would it look? Jason