From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH 27/33] dma-direct: use node local allocations for coherent memory Date: Wed, 10 Jan 2018 16:49:58 +0000 Message-ID: <3f37ba8d-66fa-80e2-bbe1-77c2a4323d6b@arm.com> References: <20180110080027.13879-1-hch@lst.de> <20180110080027.13879-28-hch@lst.de> <3672aa56-b85c-5d2c-0c0e-709031b0c0a0@arm.com> <20180110153017.GD17790@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180110153017.GD17790@lst.de> Content-Language: en-GB Sender: linux-m68k-owner@vger.kernel.org List-Id: linux-m68k@vger.kernel.org To: Christoph Hellwig Cc: iommu@lists.linux-foundation.org, linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Guan Xuetao , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, linux-hexagon@vger.kernel.org, x86@kernel.org, Konrad Rzeszutek Wilk , linux-snps-arc@lists.infradead.org, linux-m68k@lists.linux-m68k.org, patches@groups.riscv.org, linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Michal Simek , linux-parisc@vger.kernel.org, linux-cris-kernel@axis.com, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linuxppc-dev@lists.ozlabs.org On 10/01/18 15:30, Christoph Hellwig wrote: > On Wed, Jan 10, 2018 at 12:06:22PM +0000, Robin Murphy wrote: >> On 10/01/18 08:00, Christoph Hellwig wrote: >>> To preserve the x86 behavior. >> >> And combined with patch 10/22 of the SWIOTLB refactoring, this means >> SWIOTLB allocations will also end up NUMA-aware, right? Great, that's what >> we want on arm64 too :) > > Well, only for swiotlb allocations that can be satisfied by > dma_direct_alloc. If we actually have to fall back to the swiotlb > buffers there is not node affinity yet. Yeah, when I looked into it I reached the conclusion that per-node bounce buffers probably weren't worth it - if you have to bounce you've already pretty much lost the performance game, and if the CPU doing the bouncing happens to be on a different node from the device you've certainly lost either way. Per-node CMA zones we definitely *would* like, but that's a future problem (it looks technically feasible without huge infrastructure changes, but fiddly). Robin.