Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbaJCO1V (ORCPT ); Fri, 3 Oct 2014 10:27:21 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:57045 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752498AbaJCO1U (ORCPT ); Fri, 3 Oct 2014 10:27:20 -0400 Message-ID: <542EB242.4090102@hurleysoftware.com> Date: Fri, 03 Oct 2014 10:27:14 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.2 MIME-Version: 1.0 To: Akinobu Mita CC: Konrad Rzeszutek Wilk , Thomas Gleixner , LKML , Andrew Morton , Marek Szyprowski , David Woodhouse , Don Dutile , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , x86@kernel.org, iommu@lists.linux-foundation.org, Greg KH Subject: Re: [PATCH v3 0/5] enhance DMA CMA on x86 References: <1397567329-3771-1-git-send-email-akinobu.mita@gmail.com> <5426CA0A.7000806@hurleysoftware.com> <54294C0B.1060705@hurleysoftware.com> <542ABF77.1020402@hurleysoftware.com> <542B5DC2.8020806@hurleysoftware.com> <20141002164121.GF1715@laptop.dumpdata.com> <542DCB9C.4020703@hurleysoftware.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Authenticated-User: 990527 peter@hurleysoftware.com X-MT-ID: 8FA290C2A27252AACF65DBC4A42F3CE3735FB2A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02/2014 07:08 PM, Akinobu Mita wrote: > 2014-10-03 7:03 GMT+09:00 Peter Hurley : >> On 10/02/2014 12:41 PM, Konrad Rzeszutek Wilk wrote: >>> On Tue, Sep 30, 2014 at 09:49:54PM -0400, Peter Hurley wrote: >>>> On 09/30/2014 07:45 PM, Thomas Gleixner wrote: > >>>> Which is different than if the plan is to ship production units for x86; >>>> then a general purpose solution will be required. >>>> >>>> As to the good design of a general purpose solution for allocating and >>>> mapping huge order pages, you are certainly more qualified to help Akinobu >>>> than I am. >> >> What Akinobu's patches intend to support is: >> >> phys_addr = dma_alloc_coherent(dev, 64 * 1024 * 1024, &bus_addr, GFP_KERNEL); >> >> which raises three issues: >> >> 1. Where do coherent blocks of this size come from? >> 2. How to prevent fragmentation of these reserved blocks over time by >> existing DMA users? >> 3. Is this support generically required across all iommu implementations on x86? >> >> Questions 1 and 2 are non-trivial, in the general case, otherwise the page >> allocator would already do this. Simply dropping in the contiguous memory >> allocator doesn't work because CMA does not have the same policy and performance >> as the page allocator, and is already causing performance regressions even >> in the absence of huge page allocations. > > Could you take a look at the patches I sent? Can they fix these issues? > https://lkml.org/lkml/2014/9/28/110 > > With these patches, normal alloc_pages() is used for allocation first > and dma_alloc_from_contiguous() is used as a fallback. Sure, I can test these patches this weekend. Where are the unit tests? >> So that's why I raised question 3; is making the necessary compromises to support >> 64MB coherent DMA allocations across all x86 iommu implementations actually >> required? >> >> Prior to Akinobu's patches, the use of CMA by x86 iommu configurations was >> designed to be limited to testing configurations, as the introductory >> commit states: >> >> commit 0a2b9a6ea93650b8a00f9fd5ee8fdd25671e2df6 >> Author: Marek Szyprowski >> Date: Thu Dec 29 13:09:51 2011 +0100 >> >> X86: integrate CMA with DMA-mapping subsystem >> >> This patch adds support for CMA to dma-mapping subsystem for x86 >> architecture that uses common pci-dma/pci-nommu implementation. This >> allows to test CMA on KVM/QEMU and a lot of common x86 boxes. >> >> Signed-off-by: Marek Szyprowski >> Signed-off-by: Kyungmin Park >> CC: Michal Nazarewicz >> Acked-by: Arnd Bergmann >> >> >> Which brings me to my suggestion: if support for huge coherent DMA is >> required only for a special test platform, then could not this support >> be specific to a new iommu configuration, namely iommu=cma, which would >> get initialized much the same way that iommu=calgary is now. >> >> The code for such a iommu configuration would mostly duplicate >> arch/x86/kernel/pci-swiotlb.c and the CMA support would get removed from >> the other x86 iommu implementations. > > I'm not sure I read correctly, though. Can boot option 'cma=0' also > help avoiding CMA from IOMMU implementation? Maybe, but that's not an appropriate solution for distro kernels. Nor does this address configurations that want a really large CMA so 1GB huge pages can be allocated (not for DMA though). Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/