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Date: Thu, 29 Jan 2026 11:21:53 +0000
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Subject: Re: [PATCH v2 0/5] Convert riscv to use the generic iommu page table
To: Jason Gunthorpe <jgg@nvidia.com>, Vincent Chen <vincent.chen@sifive.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>, Albert Ou <aou@eecs.berkeley.edu>,
 iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>,
 linux-riscv@lists.infradead.org, Palmer Dabbelt <palmer@dabbelt.com>,
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 Will Deacon <will@kernel.org>, lihangjing@bytedance.com,
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From: Robin Murphy <robin.murphy@arm.com>
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On 2026-01-23 1:52 pm, Jason Gunthorpe wrote:
> On Fri, Jan 23, 2026 at 08:29:01PM +0800, Vincent Chen wrote:
> 
>> With this codebase, the IOMMU group type is now correctly configured as
>> DMA:
>>
>>    # cat /sys/kernel/iommu_groups/0/type
>>    DMA
>>    # cat /sys/kernel/iommu_groups/1/type
>>    DMA
>>
>> I re-ran the iperf3 test in this environment, and the test passed
>> successfully.
> 
> OK great thanks alot!
> 
> I'm surprised it doesn't say DMA-FQ, someone from RISCV may want to
> investigate that, it is probably reducing performance..

The driver does not advertise IOMMU_CAP_DEFERRED_FLUSH, as the existing 
pagetable code has never implemented the conditional TLB maintenance 
optimisation that makes it meaningful. Mind you, I don't see any 
reference to iommu_iotlb_gather_queued() in generic_pt either, so I have 
no idea how that's trying to do it :/

Thanks,
Robin.