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From:   Xinghui Li <korantwork@gmail.com>
Date:   Wed, 28 Dec 2022 10:19:58 +0800
Message-ID: <CAEm4hYXncuvL-Gk1aEZExrvkbx=N1aiOQNeNjFdB4443EbKNBA@mail.gmail.com>
Subject: Re: [PATCH] PCI: vmd: Do not disable MSI-X remapping in VMD 28C0 controller
To:     Jonathan Derrick <jonathan.derrick@linux.dev>
Cc:     Keith Busch <kbusch@kernel.org>, nirmal.patel@linux.intel.com,
        lpieralisi@kernel.org, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, Xinghui Li <korantli@tencent.com>
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Jonathan Derrick <jonathan.derrick@linux.dev> =E4=BA=8E2022=E5=B9=B412=E6=
=9C=8828=E6=97=A5=E5=91=A8=E4=B8=89 06:32=E5=86=99=E9=81=93=EF=BC=9A
>
> The bypass mode should help in the cases where drives irqs (eg nproc) exc=
eed
> VMD I/O irqs. VMD I/O irqs for 28c0 should be min(63, nproc). You have
> very few cpus for a Skylake system with that many drives, unless you mean=
 you
> are explicitly restricting the 12 drives to only 6 cpus. Either way, bypa=
ss mode
> is effectively VMD-disabled, which points to other issues. Though I have =
also seen
> much smaller interrupt aggregation benefits.

Firstly=EF=BC=8CI am sorry for my words misleading you. We totally tested 1=
2 drives.
And each drive run in 6 CPU cores with 8 jobs.

Secondly, I try to test the drives with VMD disabled,I found the results to
be largely consistent with bypass mode. I suppose the bypass mode just
"bypass" the VMD controller.

The last one=EF=BC=8Cwe found in bypass mode the CPU idle is 91%. But in re=
mapping mode
the CPU idle is 78%. And the bypass's context-switchs is much fewer
than the remapping
mode's. It seems the system is watiing for something in bypass mode.