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Subject: Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO
 from remote numa node
To:     Marc Zyngier <maz@kernel.org>
CC:     Ming Lei <ming.lei@redhat.com>,
        Robin Murphy <robin.murphy@arm.com>,
        <iommu@lists.linux-foundation.org>, Will Deacon <will@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
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From:   John Garry <john.garry@huawei.com>
Message-ID: <d975276a-5889-7bbd-5329-287ae661f04b@huawei.com>
Date:   Thu, 22 Jul 2021 14:54:44 +0100
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On 22/07/2021 13:53, Marc Zyngier wrote:
> Hi John,
> 
> [...]
> 
>>     Your kernel log should show:
>>     [    0.000000] GICv3: Pseudo-NMIs enabled using forced ICC_PMR_EL1
>> synchronisation
> 
> Unrelated, but you seem to be running with ICC_CTLR_EL3.PMHE set,
> which makes the overhead of pseudo-NMIs much higher than it should be
> (you take a DSB SY on each interrupt unmasking).
> 
> If you are not using 1:N distribution of SPIs on the secure side,
> consider turning that off in your firmware. This should make NMIs
> slightly more pleasant to use.

Thanks for the hint. I speak to the BIOS guys.

John