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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 98BA5C433F5 for ; Tue, 14 Sep 2021 09:38:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 666E9610A2 for ; Tue, 14 Sep 2021 09:38:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229686AbhINJjv (ORCPT ); Tue, 14 Sep 2021 05:39:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229699AbhINJjr (ORCPT ); Tue, 14 Sep 2021 05:39:47 -0400 Received: from mail-ot1-x336.google.com (mail-ot1-x336.google.com [IPv6:2607:f8b0:4864:20::336]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D31B7C061574 for ; Tue, 14 Sep 2021 02:38:30 -0700 (PDT) Received: by mail-ot1-x336.google.com with SMTP id a20-20020a0568300b9400b0051b8ca82dfcso17537158otv.3 for ; Tue, 14 Sep 2021 02:38:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=7KFN+kOEbLRU1oyPcn4BCimcXnbrpcLqySWxj76DlhI=; b=JgVbjJ75UrN18+bBF/j8/i+LBvcB0MZGfdx4xOshFvwcMRJ9NPc6EV9engeZNVyhIC 7QiIuvzHXu2cxIr4Wmmn6J1izEk86IRYYGJnM78xdrIx/q1g5YMhFfAvcmtyiAd59Wly 1G3bK/DaFcn/PrCCk7VETq8KaQhk0QxAsysxo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=7KFN+kOEbLRU1oyPcn4BCimcXnbrpcLqySWxj76DlhI=; b=xf6RxXQasZxE7uXjbwtU9CWVjJVmKHZB7RrvJc1Nu1k5HbIGf5cxaor+iiORADk9B7 xODVMJsq2k9Rp+7ARdOXXIoz/+vqXUbs33ZdmEcWFUNLjXCz4ybWsZUPn3E7M0dOCV+U 31VD8fkSMbxJ5qDTsQn+NZe5Fjav5BQG99MiymvdpPvZysCZoYkDM1stpjC5/GEtOTcX 84HabB8VUiQTac6Cpde0ol1oiF98UEwqbGrOiV506E7Xkq0vPQYbfxSdNOC4HWOmGdyp wKSzAHpMuqsbJmkwS8r/Rt3c4wGYcumCmKri4CnIgoq0bKiS7rK4u7ISHL66clttqxiT EhXQ== X-Gm-Message-State: AOAM532Ex7HxdIrYUT7kvMFmxFoHBO3vQx0S5zGeiJ5mtFCFL+M2JmME ZQ9tQbp1mtMHFm99ufe7tHBuJ4tOb2GtzMzAY4aNrQ== X-Google-Smtp-Source: ABdhPJwKH2tOW/CaIyEIXPAZeV5hHj6hSHYMa81lXis87njsxExJlKwCiUdBXL4uQQHYu4Zpo9i5or65E1BU2aEgrgU= X-Received: by 2002:a9d:67c1:: with SMTP id c1mr13774657otn.239.1631612310212; Tue, 14 Sep 2021 02:38:30 -0700 (PDT) MIME-Version: 1.0 References: <20210908061611.69823-1-mie@igel.co.jp> <20210908061611.69823-2-mie@igel.co.jp> <20210908111804.GX1200268@ziepe.ca> <1c0356f5-19cf-e883-3d96-82a87d0cffcb@amd.com> <20210908233354.GB3544071@ziepe.ca> In-Reply-To: From: Daniel Vetter Date: Tue, 14 Sep 2021 11:38:19 +0200 Message-ID: Subject: Re: [RFC PATCH 1/3] RDMA/umem: Change for rdma devices has not dma device To: Shunsuke Mie Cc: Jason Gunthorpe , =?UTF-8?Q?Christian_K=C3=B6nig?= , Christoph Hellwig , Zhu Yanjun , Alex Deucher , Doug Ledford , Jianxin Xiong , Leon Romanovsky , Linux Kernel Mailing List , linux-rdma , Damian Hobson-Garcia , Takanari Hayama , Tomohito Esaki Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Tue, Sep 14, 2021 at 9:11 AM Shunsuke Mie wrote: > > 2021=E5=B9=B49=E6=9C=8814=E6=97=A5(=E7=81=AB) 4:23 Daniel Vetter : > > > > On Fri, Sep 10, 2021 at 3:46 AM Shunsuke Mie wrote: > > > > > > 2021=E5=B9=B49=E6=9C=889=E6=97=A5(=E6=9C=A8) 18:26 Daniel Vetter : > > > > > > > > On Thu, Sep 9, 2021 at 1:33 AM Jason Gunthorpe wrote= : > > > > > On Wed, Sep 08, 2021 at 09:22:37PM +0200, Daniel Vetter wrote: > > > > > > On Wed, Sep 8, 2021 at 3:33 PM Christian K=C3=B6nig wrote: > > > > > > > Am 08.09.21 um 13:18 schrieb Jason Gunthorpe: > > > > > > > > On Wed, Sep 08, 2021 at 05:41:39PM +0900, Shunsuke Mie wrot= e: > > > > > > > >> 2021=E5=B9=B49=E6=9C=888=E6=97=A5(=E6=B0=B4) 16:20 Christo= ph Hellwig : > > > > > > > >>> On Wed, Sep 08, 2021 at 04:01:14PM +0900, Shunsuke Mie wr= ote: > > > > > > > >>>> Thank you for your comment. > > > > > > > >>>>> On Wed, Sep 08, 2021 at 03:16:09PM +0900, Shunsuke Mie = wrote: > > > > > > > >>>>>> To share memory space using dma-buf, a API of the dma-= buf requires dma > > > > > > > >>>>>> device, but devices such as rxe do not have a dma devi= ce. For those case, > > > > > > > >>>>>> change to specify a device of struct ib instead of the= dma device. > > > > > > > >>>>> So if dma-buf doesn't actually need a device to dma map= why do we ever > > > > > > > >>>>> pass the dma_device here? Something does not add up. > > > > > > > >>>> As described in the dma-buf api guide [1], the dma_devic= e is used by dma-buf > > > > > > > >>>> exporter to know the device buffer constraints of import= er. > > > > > > > >>>> [1] https://nam11.safelinks.protection.outlook.com/?url= =3Dhttps%3A%2F%2Flwn.net%2FArticles%2F489703%2F&data=3D04%7C01%7Cchrist= ian.koenig%40amd.com%7C4d18470a94df4ed24c8108d972ba5591%7C3dd8961fe4884e608= e11a82d994e183d%7C0%7C0%7C637666967356417448%7CUnknown%7CTWFpbGZsb3d8eyJWIj= oiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sda= ta=3DARwQyo%2BCjMohaNbyREofToHIj2bndL5L0HaU9cOrYq4%3D&reserved=3D0 > > > > > > > >>> Which means for rxe you'd also have to pass the one for t= he underlying > > > > > > > >>> net device. > > > > > > > >> I thought of that way too. In that case, the memory region= is constrained by the > > > > > > > >> net device, but rxe driver copies data using CPU. To avoid= the constraints, I > > > > > > > >> decided to use the ib device. > > > > > > > > Well, that is the whole problem. > > > > > > > > > > > > > > > > We can't mix the dmabuf stuff people are doing that doesn't= fill in > > > > > > > > the CPU pages in the SGL with RXE - it is simply impossible= as things > > > > > > > > currently are for RXE to acess this non-struct page memory. > > > > > > > > > > > > > > Yeah, agree that doesn't make much sense. > > > > > > > > > > > > > > When you want to access the data with the CPU then why do you= want to > > > > > > > use DMA-buf in the first place? > > > > > > > > > > > > > > Please keep in mind that there is work ongoing to replace the= sg table > > > > > > > with an DMA address array and so make the underlying struct p= age > > > > > > > inaccessible for importers. > > > > > > > > > > > > Also if you do have a dma-buf, you can just dma_buf_vmap() the = buffer > > > > > > for cpu access. Which intentionally does not require any device= . No > > > > > > idea why there's a dma_buf_attach involved. Now not all exporte= rs > > > > > > support this, but that's fixable, and you must call > > > > > > dma_buf_begin/end_cpu_access for cache management if the alloca= tion > > > > > > isn't cpu coherent. But it's all there, no need to apply hacks = of > > > > > > allowing a wrong device or other fun things. > > > > > > > > > > Can rxe leave the vmap in place potentially forever? > > > > > > > > Yeah, it's like perma-pinning the buffer into system memory for > > > > non-p2p dma-buf sharing. We just squint and pretend that can't be > > > > abused too badly :-) On 32bit you'll run out of vmap space rather > > > > quickly, but that's not something anyone cares about here either. W= e > > > > have a bunch of more sw modesetting drivers in drm which use > > > > dma_buf_vmap() like this, so it's all fine. > > > > -Daniel > > > > -- > > > > Daniel Vetter > > > > Software Engineer, Intel Corporation > > > > http://blog.ffwll.ch > > > > > > Thanks for your comments. > > > > > > In the first place, the CMA region cannot be used for RDMA because th= e > > > region has no struct page. In addition, some GPU drivers use CMA and = share > > > the region as dma-buf. As a result, RDMA cannot transfer for the regi= on. To > > > solve this problem, rxe dma-buf support is better I thought. > > > > > > I'll consider and redesign the rxe dma-buf support using the dma_buf_= vmap() > > > instead of the dma_buf_dynamic_attach(). > > > > btw for next version please cc dri-devel. get_maintainers.pl should > > pick it up for these patches. > A CC list of these patches is generated by get_maintainers.pl but it > didn't pick up the dri-devel. Should I add the dri-devel to the cc > manually? Hm yes, on rechecking the regex doesn't match since you're not touching any dma-buf code directly. Or not directly enough for get_maintainers.pl to pick it up. DMA BUFFER SHARING FRAMEWORK M: Sumit Semwal M: Christian K=C3=B6nig L: linux-media@vger.kernel.org L: dri-devel@lists.freedesktop.org L: linaro-mm-sig@lists.linaro.org (moderated for non-subscribers) S: Maintained T: git git://anongit.freedesktop.org/drm/drm-misc F: Documentation/driver-api/dma-buf.rst F: drivers/dma-buf/ F: include/linux/*fence.h F: include/linux/dma-buf* F: include/linux/dma-resv.h K: \bdma_(?:buf|fence|resv)\b Above is the MAINTAINERS entry that's always good to cc for anything related to dma_buf/fence/resv and any of these related things. -Daniel --=20 Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch