Messages in this thread | | | Date | Thu, 23 Jul 2020 13:55:27 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH v3 1/2] dma-direct: provide the ability to reserve per-numa CMA |
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On Wed, Jul 22, 2020 at 09:26:03PM +0000, Song Bao Hua (Barry Song) wrote: > I understand your concern. Anyway, The primary purpose of this patchset is providing > a general way for users like IOMMU to get local coherent dma buffers to put their > command queue and page tables in. The first user case is what really made me > begin to prepare this patchset. > > For the second case, it is probably a positive side effect of this patchset for those users > who have more concern on performance than dma security, then they maybe skip > IOMMU by > iommu.passthrough= > [ARM64, X86] Configure DMA to bypass the IOMMU by default. > Format: { "0" | "1" } > 0 - Use IOMMU translation for DMA. > 1 - Bypass the IOMMU for DMA. > unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. > In this case, they can get local memory and get better performance. > However, it is not the primary purpose of this patchset.
That's not what I mean. Hardcoding the CMA regions in the kernel config is just a bad idea, and we should not add more hard coded values. You can always use CONFIG_CMDLINE to force a specific kernel command line including your options.
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