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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 /Documentation | |
| parent | Linux 5.9-rc3 (diff) | |
| download | linux-dev-b7176c261cdbced87bed9562577333150ed05b01.tar.xz linux-dev-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 'Documentation')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index a1068742a6df..e464cf0b5025 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -599,6 +599,17 @@ altogether. For more information, see include/linux/dma-contiguous.h + cma_pernuma=nn[MG] + [ARM64,KNL] + Sets the size of kernel per-numa memory area for + contiguous memory allocations. A value of 0 disables + per-numa CMA altogether. And If this option is not + specificed, the default value is 0. + With per-numa CMA enabled, DMA users on node nid will + first try to allocate buffer from the pernuma area + which is located in node nid, if the allocation fails, + they will fallback to the global default memory area. + cmo_free_hint= [PPC] Format: { yes | no } Specify whether pages are marked as being inactive when they are freed. This is used in CMO environments |