netdev - Re: Regression 5.12.0-rc4 net: ice: significant throughput drop

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Date:   Tue, 1 Jun 2021 19:42:07 +0200
From:   Jussi Maki <joamaki@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, jroedel@...e.de,
        netdev@...r.kernel.org, bpf <bpf@...r.kernel.org>,
        intel-wired-lan@...ts.osuosl.org, davem@...emloft.net,
        anthony.l.nguyen@...el.com, jesse.brandeburg@...el.com, hch@....de,
        iommu@...ts.linux-foundation.org, suravee.suthikulpanit@....com
Subject: Re: Regression 5.12.0-rc4 net: ice: significant throughput drop

Hi Robin,

On Tue, Jun 1, 2021 at 2:39 PM Robin Murphy <robin.murphy@....com> wrote:
> >> The regression shows as a significant drop in throughput as measured
> >> with "super_netperf" [0],
> >> with measured bandwidth of ~95Gbps before and ~35Gbps after:
>
> I guess that must be the difference between using the flush queue
> vs. strict invalidation. On closer inspection, it seems to me that
> there's a subtle pre-existing bug in the AMD IOMMU driver, in that
> amd_iommu_init_dma_ops() actually runs *after* amd_iommu_init_api()
> has called bus_set_iommu(). Does the patch below work?

Thanks for the quick response & patch. I tried it out and indeed it
does solve the issue:

# uname -a
Linux zh-lab-node-3 5.13.0-rc3-amd-iommu+ #31 SMP Tue Jun 1 17:12:57
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
root@...lab-node-3:~# ./super_netperf 32 -H 172.18.0.2
95341.2

root@...lab-node-3:~# uname -a
Linux zh-lab-node-3 5.13.0-rc3-amd-iommu-unpatched #32 SMP Tue Jun 1
17:29:34 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
root@...lab-node-3:~# ./super_netperf 32 -H 172.18.0.2
33989.5