linux-kernel - Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node

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Date:   Mon, 26 Jul 2021 08:51:32 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>, Robin Murphy <robin.murphy@....com>
CC:     <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO
 from remote numa node

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