Re: [PATCH 27/33] dma-direct: use node local allocations for coherent memory
From: Robin Murphy <robin.murphy@arm.com>
Date: 2018-01-10 16:50:08
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linux-alpha, linux-arch, linux-arm-kernel, linux-iommu, linux-m68k, linux-mips, linux-s390, linux-sh, lkml, sparclinux
On 10/01/18 15:30, Christoph Hellwig wrote:
On Wed, Jan 10, 2018 at 12:06:22PM +0000, Robin Murphy wrote:quoted
On 10/01/18 08:00, Christoph Hellwig wrote:quoted
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.