From: Christoph Hellwig <hch@lst.de>
To: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
Cc: "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
Steve Capper <steve.capper@arm.com>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
Jonathan Cameron <jonathan.cameron@huawei.com>,
Linuxarm <linuxarm@huawei.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
"Zengtao \(B\)" <prime.zeng@hisilicon.com>,
"ganapatrao.kulkarni@cavium.com" <ganapatrao.kulkarni@cavium.com>,
huangdaode <huangdaode@huawei.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@linux.ibm.com>,
"will@kernel.org" <will@kernel.org>,
Christoph Hellwig <hch@lst.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"m.szyprowski@samsung.com" <m.szyprowski@samsung.com>
Subject: Re: [PATCH v3 1/2] dma-direct: provide the ability to reserve per-numa CMA
Date: Thu, 23 Jul 2020 13:55:27 +0200 [thread overview]
Message-ID: <20200723115527.GA31598@lst.de> (raw)
In-Reply-To: <B926444035E5E2439431908E3842AFD25A15A3@DGGEMI525-MBS.china.huawei.com>
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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next prev parent reply other threads:[~2020-07-23 11:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-28 11:12 [PATCH v3 0/2] make dma_alloc_coherent NUMA-aware by per-NUMA CMA Barry Song
2020-06-28 11:12 ` [PATCH v3 1/2] dma-direct: provide the ability to reserve per-numa CMA Barry Song
2020-07-22 14:16 ` Christoph Hellwig
2020-07-22 21:26 ` Song Bao Hua (Barry Song)
2020-07-23 11:55 ` Christoph Hellwig [this message]
2020-07-22 14:29 ` Christoph Hellwig
2020-07-22 21:41 ` Song Bao Hua (Barry Song)
2020-07-23 12:00 ` Christoph Hellwig
2020-07-23 12:08 ` Song Bao Hua (Barry Song)
2020-06-28 11:12 ` [PATCH v3 2/2] arm64: mm: reserve per-numa CMA to localize coherent dma buffers Barry Song
2020-07-13 2:45 ` [PATCH v3 0/2] make dma_alloc_coherent NUMA-aware by per-NUMA CMA Song Bao Hua (Barry Song)
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