From mboxrd@z Thu Jan 1 00:00:00 1970 From: "hch@lst.de" Subject: Re: [PATCH] lib/scatterlist: Provide a DMA page iterator Date: Tue, 15 Jan 2019 19:31:33 +0100 Message-ID: <20190115183133.GA12350@lst.de> References: <20190104223531.GA1705@ziepe.ca> <20190110234218.GM6890@ziepe.ca> <20190114094856.GB29604@lst.de> <1fb20ab4b171b281e9994b6c55734c120958530b.camel@vmware.com> <2b440a3b-ed2f-8fd6-a21e-97ca0b2f5db9@gmail.com> <20190115152029.GB2325@lst.de> <41d0616e95fb48942404fb54d82249f5700affb1.camel@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <41d0616e95fb48942404fb54d82249f5700affb1.camel@vmware.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Thomas Hellstrom Cc: "linux-rdma@vger.kernel.org" , "daniel.vetter@ffwll.ch" , "jian.xu.zheng@intel.com" , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "christian.koenig@amd.com" , "jgg@ziepe.ca" , "sakari.ailus@linux.intel.com" , "bingbu.cao@intel.com" , "linux-media@vger.kernel.org" , "shiraz.saleem@intel.com" , "hch@lst.de" , "tian.shu.qiu@intel.com" , "yong.zhi@intel.com" List-Id: linux-rdma@vger.kernel.org T24gVHVlLCBKYW4gMTUsIDIwMTkgYXQgMDY6MDM6MzlQTSArMDAwMCwgVGhvbWFzIEhlbGxzdHJv bSB3cm90ZToKPiBJbiB0aGUgZ3JhcGhpY3MgY2FzZSwgaXQncyBwcm9iYWJseSBiZWNhdXNlIGl0 IGRvZXNuJ3QgZml0IHRoZSBncmFwaGljcwo+IHVzZS1jYXNlczoKPiAKPiAxKSBNZW1vcnkgdHlw aWNhbGx5IG5lZWRzIHRvIGJlIG1hcHBhYmxlIGJ5IGFub3RoZXIgZGV2aWNlLiAodGhlICJkbWEt Cj4gYnVmIiBpbnRlcmZhY2UpCgpBbmQgdGhlcmUgaXMgbm90aGluZyBwcmV2ZW50aW5nIGRtYS1i dWYgc2hhcmluZyBvZiB0aGVzZSBidWZmZXJzLgpVbmxpa2UgdGhlIGdldF9zZ3RhYmxlIG1lc3Mg aXQgY2FuIGFjdHVhbGx5IHdvcmsgcmVsaWFibHkgb24KYXJjaGl0ZWN0dXJlcyB0aGF0IGhhdmUg dmlydHVhbGx5IHRhZ2dlZCBjYWNoZXMgYW5kL29yIGRvbid0Cmd1YXJhbnRlZSBjYWNoZSBjb2hl cmVuY3kgd2l0aCBtaXhlZCBhdHRyaWJ1dGUgbWFwcGluZ3MuCgo+IDIpIERNQSBidWZmZXJzIGFy ZSBleHBvcnRlZCB0byB1c2VyLXNwYWNlIGFuZCBpcyBzdWItYWxsb2NhdGVkIGJ5IGl0Lgo+IE1v c3RseSB0aGVyZSBhcmUgbm8gR1BVIHVzZXItc3BhY2Uga2VybmVsIGludGVyZmFjZXMgdG8gc3lu YyAvIGZsdXNoCj4gc3VicmVnaW9ucyBhbmQgdGhlc2Ugc3luY3MgbWF5IGhhcHBlbiBvbiBhIHNt YWxsZXItdGhhbi1jYWNoZS1saW5lCj4gZ3JhbnVsYXJpdHkuCgpJIGtub3cgb2Ygbm8gYXJjaGl0 ZWN0dXJlcyB0aGF0IGNhbiBkbyBjYWNoZSBtYWludGFpbmFuY2Ugb24gYSBsZXNzCnRoYW4gY2Fj aGUgbGluZSBiYXNpcy4gIEVpdGhlciB0aGUgaW5zdHJ1Y3Rpb25zIHJlcXVpcmUgeW91IHRvCnNw ZWNpZmN5IGNhY2hlIGxpbmVzLCBvciB0aGV5IGRvIHNvbWV0aW1lcyBtb3JlLCBzb21ldGltZXMg bGVzcwppbnRlbGxpZ2VudCByb3VuZGluZyB1cC4KCk5vdGUgdGhhdCBhcyBsb25nIGRtYSBub24t Y29oZXJlbnQgYnVmZmVycyBhcmUgZGV2aWNlcyBvd25lZCBpdAppcyB1cCB0byB0aGUgZGV2aWNl IGFuZCB0aGUgdXNlciBzcGFjZSBkcml2ZXIgdG8gdGFrZSBjYXJlIG9mCmNvaGVyZW5jeSwgdGhl IGtlcm5lbCB2ZXJ5IG11Y2ggaXMgb3V0IG9mIHRoZSBwaWN0dXJlLgpfX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpkcmktZGV2ZWwgbWFpbGluZyBsaXN0CmRy aS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5vcmcKaHR0cHM6Ly9saXN0cy5mcmVlZGVza3RvcC5v cmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2ZWwK 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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E2837C43387 for ; Tue, 15 Jan 2019 18:31:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B6D0B20859 for ; Tue, 15 Jan 2019 18:31:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732240AbfAOSbf (ORCPT ); Tue, 15 Jan 2019 13:31:35 -0500 Received: from verein.lst.de ([213.95.11.211]:54742 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727088AbfAOSbf (ORCPT ); Tue, 15 Jan 2019 13:31:35 -0500 Received: by newverein.lst.de (Postfix, from userid 2407) id 3C74667358; Tue, 15 Jan 2019 19:31:33 +0100 (CET) Date: Tue, 15 Jan 2019 19:31:33 +0100 From: "hch@lst.de" To: Thomas Hellstrom Cc: "hch@lst.de" , "christian.koenig@amd.com" , "linux-kernel@vger.kernel.org" , "yong.zhi@intel.com" , "daniel.vetter@ffwll.ch" , "linux-rdma@vger.kernel.org" , "linux-media@vger.kernel.org" , "bingbu.cao@intel.com" , "jian.xu.zheng@intel.com" , "tian.shu.qiu@intel.com" , "shiraz.saleem@intel.com" , "sakari.ailus@linux.intel.com" , "dri-devel@lists.freedesktop.org" , "jgg@ziepe.ca" Subject: Re: [PATCH] lib/scatterlist: Provide a DMA page iterator Message-ID: <20190115183133.GA12350@lst.de> References: <20190104223531.GA1705@ziepe.ca> <20190110234218.GM6890@ziepe.ca> <20190114094856.GB29604@lst.de> <1fb20ab4b171b281e9994b6c55734c120958530b.camel@vmware.com> <2b440a3b-ed2f-8fd6-a21e-97ca0b2f5db9@gmail.com> <20190115152029.GB2325@lst.de> <41d0616e95fb48942404fb54d82249f5700affb1.camel@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41d0616e95fb48942404fb54d82249f5700affb1.camel@vmware.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 15, 2019 at 06:03:39PM +0000, Thomas Hellstrom wrote: > In the graphics case, it's probably because it doesn't fit the graphics > use-cases: > > 1) Memory typically needs to be mappable by another device. (the "dma- > buf" interface) And there is nothing preventing dma-buf sharing of these buffers. Unlike the get_sgtable mess it can actually work reliably on architectures that have virtually tagged caches and/or don't guarantee cache coherency with mixed attribute mappings. > 2) DMA buffers are exported to user-space and is sub-allocated by it. > Mostly there are no GPU user-space kernel interfaces to sync / flush > subregions and these syncs may happen on a smaller-than-cache-line > granularity. I know of no architectures that can do cache maintainance on a less than cache line basis. Either the instructions require you to specifcy cache lines, or they do sometimes more, sometimes less intelligent rounding up. Note that as long dma non-coherent buffers are devices owned it is up to the device and the user space driver to take care of coherency, the kernel very much is out of the picture.