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From: Kunkun Jiang <jiangkunkun@huawei.com>
To: Robin Murphy <robin.murphy@arm.com>,
	Will Deacon <will@kernel.org>,
	"Linux IOMMU" <iommu@lists.linux-foundation.org>,
	open list <linux-kernel@vger.kernel.org>
Cc: <wanghaibin.wang@huawei.com>, Zenghui Yu <yuzenghui@huawei.com>,
	"Keqian Zhu" <zhukeqian1@huawei.com>
Subject: [question] Assign multiple devices from different SMMUs to a arm_smmu_domain
Date: Tue, 7 Sep 2021 15:41:52 +0800	[thread overview]
Message-ID: <bbfcb875-0da1-c303-ed48-fdaa890c89b3@huawei.com> (raw)

Hi all,

I am working on VFIO DMA dirty pages tracking based on ARM SMMU HTTU,
and have done a lot of testing.In the test, I found a problem that 
greatly affects
performance of VFIO DMA dirty pages tracking.

According to the current arm-smmu-v3 driver, multiple VFIO pass-through
device comes from different SMMUs will be assigned to different
arm_smmu_domain. It will create page table for each arm_smmu_domain,
even though these page tables are exactly the same. Bacause dirty pages
tracking needs to traverse the page table, multiple page tables will make
performance worse.

I learned the ARM SMMUv3 spec and had some exchanges with my colleagues
who work on SMMU hardware. I did not find the restriction that multiple
SMMUs cannot share the same page table. We migth be able to do this like
x86 IOMMU. If I have missed something, please point it out.

Looking forward to your suggestions.😁

Thanks,
Kunkun Jiang


             reply	other threads:[~2021-09-07  7:42 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-07  7:41 Kunkun Jiang [this message]
2021-09-07  9:43 ` [question] Assign multiple devices from different SMMUs to a arm_smmu_domain Robin Murphy
2021-09-08  5:06   ` Kunkun Jiang

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