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Subject: Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO
 from remote numa node
To:     Ming Lei <ming.lei@redhat.com>, Robin Murphy <robin.murphy@arm.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
        <iommu@lists.linux-foundation.org>, Will Deacon <will@kernel.org>,
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From:   John Garry <john.garry@huawei.com>
Message-ID: <6ceab844-465f-3bf3-1809-5df1f1dbbc5c@huawei.com>
Date:   Mon, 26 Jul 2021 08:51:32 +0100
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On 23/07/2021 11:21, Ming Lei wrote:
>> Thanks, I was also going to suggest the latter, since it's what
>> arm_smmu_cmdq_issue_cmdlist() does with IRQs masked that should be most
>> indicative of where the slowness most likely stems from.
> The improvement from 'iommu.strict=0' is very small:
> 

Have you tried turning off the IOMMU to ensure that this is really just 
an IOMMU problem?

You can try setting CONFIG_ARM_SMMU_V3=n in the defconfig or passing 
cmdline param iommu.passthrough=1 to bypass the the SMMU (equivalent to 
disabling for kernel drivers).

Thanks,
John