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authorBarry Song <song.bao.hua@hisilicon.com>2020-08-24 02:03:07 +0300
committerChristoph Hellwig <hch@lst.de>2020-09-01 10:19:28 +0300
commitb7176c261cdbced87bed9562577333150ed05b01 (patch)
tree97b2ca14fd7833dbb40cee18082b0b1a93157605 /mm/Kconfig
parentf75aef392f869018f78cfedf3c320a6b3fcfda6b (diff)
downloadlinux-b7176c261cdbced87bed9562577333150ed05b01.tar.xz
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 'mm/Kconfig')
-rw-r--r--mm/Kconfig3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index 6c974888f86f..d75a0107f61f 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -516,13 +516,14 @@ config CMA_DEBUGFS
config CMA_AREAS
int "Maximum count of the CMA areas"
depends on CMA
+ default 19 if NUMA
default 7
help
CMA allows to create CMA areas for particular purpose, mainly,
used as device private area. This parameter sets the maximum
number of CMA area in the system.
- If unsure, leave the default value "7".
+ If unsure, leave the default value "7" in UMA and "19" in NUMA.
config MEM_SOFT_DIRTY
bool "Track memory changes"