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| author | Barry Song <song.bao.hua@hisilicon.com> | 2020-08-24 11:03:07 +1200 |
|---|---|---|
| committer | Christoph Hellwig <hch@lst.de> | 2020-09-01 09:19:28 +0200 |
| commit | b7176c261cdbced87bed9562577333150ed05b01 (patch) | |
| tree | 97b2ca14fd7833dbb40cee18082b0b1a93157605 /kernel/dma/Kconfig | |
| parent | f75aef392f869018f78cfedf3c320a6b3fcfda6b (diff) | |
| download | lwn-b7176c261cdbced87bed9562577333150ed05b01.tar.gz lwn-b7176c261cdbced87bed9562577333150ed05b01.zip | |
dma-contiguous: provide the ability to reserve per-numa CMA
Right now, drivers like ARM SMMU are using dma_alloc_coherent() to get
coherent DMA buffers to save their command queues and page tables. As
there is only one default CMA in the whole system, SMMUs on nodes other
than node0 will get remote memory. This leads to significant latency.
This patch provides per-numa CMA so that drivers like SMMU can get local
memory. Tests show localizing CMA can decrease dma_unmap latency much.
For instance, before this patch, SMMU on node2 has to wait for more than
560ns for the completion of CMD_SYNC in an empty command queue; with this
patch, it needs 240ns only.
A positive side effect of this patch would be improving performance even
further for those users who are worried about performance more than DMA
security and use iommu.passthrough=1 to skip IOMMU. With local CMA, all
drivers can get local coherent DMA buffers.
Also, this patch changes the default CONFIG_CMA_AREAS to 19 in NUMA. As
1+CONFIG_CMA_AREAS should be quite enough for most servers on the market
even they enable both hugetlb_cma and pernuma_cma.
2 numa nodes: 2(hugetlb) + 2(pernuma) + 1(default global cma) = 5
4 numa nodes: 4(hugetlb) + 4(pernuma) + 1(default global cma) = 9
8 numa nodes: 8(hugetlb) + 8(pernuma) + 1(default global cma) = 17
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'kernel/dma/Kconfig')
| -rw-r--r-- | kernel/dma/Kconfig | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig index 847a9d1fa634..0ddfb5510fe4 100644 --- a/kernel/dma/Kconfig +++ b/kernel/dma/Kconfig @@ -118,6 +118,17 @@ config DMA_CMA If unsure, say "n". if DMA_CMA + +config DMA_PERNUMA_CMA + bool "Enable separate DMA Contiguous Memory Area for each NUMA Node" + default NUMA && ARM64 + help + Enable this option to get pernuma CMA areas so that devices like + ARM64 SMMU can get local memory by DMA coherent APIs. + + You can set the size of pernuma CMA by specifying "cma_pernuma=size" + on the kernel's command line. + comment "Default contiguous memory area size:" config CMA_SIZE_MBYTES |