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

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Message-ID: <YQF1AKS6Y14dLU/A@T590>
Date:   Wed, 28 Jul 2021 23:17:20 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Robin Murphy <robin.murphy@....com>, 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 Wed, Jul 28, 2021 at 11:38:18AM +0100, John Garry wrote:
> On 28/07/2021 02:32, Ming Lei wrote:
> > On Mon, Jul 26, 2021 at 3:51 PM John Garry<john.garry@...wei.com>  wrote:
> > > 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).
> > Bypassing SMMU via iommu.passthrough=1 basically doesn't make a difference
> > on this issue.
> 
> A ~90% throughput drop still seems to me to be too high to be a software
> issue. More so since I don't see similar on my system. And that throughput
> drop does not lead to a total CPU usage drop, from the fio log.
> 
> Do you know if anyone has run memory benchmark tests on this board to find
> out NUMA effect? I think lmbench or stream could be used for this.

https://lore.kernel.org/lkml/YOhbc5C47IzC893B@T590/

-- 
Ming