netdev - Re: AMD IOMMU problem after NIC uses multi-page allocation

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Message-ID: <ab6265e3-5adf-1129-fba7-cbcd2e6776b5@amd.com>
Date:   Thu, 30 Mar 2023 17:37:35 +0530
From:   Vasant Hegde <vasant.hegde@....com>
To:     Joerg Roedel <joro@...tes.org>, Jakub Kicinski <kuba@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Cc:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu@...ts.linux.dev,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Saeed Mahameed <saeed@...nel.org>
Subject: Re: AMD IOMMU problem after NIC uses multi-page allocation

Hi Jakub,

On 3/30/2023 1:11 PM, Joerg Roedel wrote:
> Also adding Vasant and Robin.
> 
> Vasant, Robin, any idea?
> 

I tried few things on my Milan system. I can't reproduce the issue.

Can you please try the patch mentioned by Yunsheng?

If its still an issue, can you please provide steps to reproduce? I will take a
look.

-Vasant


> On Wed, Mar 29, 2023 at 06:14:07PM -0700, Jakub Kicinski wrote:
>> Hi Joerg, Suravee,
>>
>> I see an odd NIC behavior with AMD IOMMU in lazy mode (on 5.19).
>>
>> The NIC allocates a buffer for Rx packets which is MTU rounded up 
>> to page size. If I run it with 1500B MTU or 9000 MTU everything is
>> fine, slight but manageable perf hit.
>>
>> But if I flip the MTU to 9k, run some traffic and then go back to 1.5k 
>> - 70%+ of CPU cycles are spent in alloc_iova (and children).
>>
>> Does this ring any bells?