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From:   Xinghui Li <korantwork@gmail.com>
Date:   Mon, 6 Feb 2023 20:45:57 +0800
Message-ID: <CAEm4hYWeZFrYxSvAcBJ8iw=t507vZMqfBwiQXFSJd2Hcyfw7fA@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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Friendly ping~

Xinghui Li <korantwork@gmail.com> =E4=BA=8E2023=E5=B9=B41=E6=9C=8810=E6=97=
=A5=E5=91=A8=E4=BA=8C 20:28=E5=86=99=E9=81=93=EF=BC=9A
>
> Jonathan Derrick <jonathan.derrick@linux.dev> =E4=BA=8E2023=E5=B9=B41=E6=
=9C=8810=E6=97=A5=E5=91=A8=E4=BA=8C 05:00=E5=86=99=E9=81=93=EF=BC=9A
> >
> > As the bypass mode seems to affect performance greatly depending on the=
 specific configuration,
> > it may make sense to use a moduleparam to control it
> >
> We found that each pcie port can mount four drives. If we only test 2
> or 1 dirve of one pcie port,
> the performance of the drive performance will be normal. Also, we
> observed the interruptions in different modes.
> bypass:
> .....
> 2022-12-28-11-39-14: 1224       181665   IR-PCI-MSI 201850948-edge      n=
vme0q68
> 2022-12-28-11-39-14: 1179       180115   IR-PCI-MSI 201850945-edge      n=
vme0q65
> 2022-12-28-11-39-14:  RES        26743   Rescheduling interrupts
> 2022-12-28-11-39-17: irqtop - IRQ : 3029, TOTAL : 2100315228, CPU :
> 192, ACTIVE CPU : 192
> disable:
> ......
> 2022-12-28-12-05-56: 1714       169797   IR-PCI-MSI 14155850-edge      nv=
me1q74
> 2022-12-28-12-05-56: 1701       168753   IR-PCI-MSI 14155849-edge      nv=
me1q73
> 2022-12-28-12-05-56:  LOC       163697   Local timer interrupts
> 2022-12-28-12-05-56:  TLB         5465   TLB shootdowns
> 2022-12-28-12-06-00: irqtop - IRQ : 3029, TOTAL : 2179022106, CPU :
> 192, ACTIVE CPU : 192
> remapping:
> 022-12-28-11-25-38:  283       325568   IR-PCI-MSI 24651790-edge      vmd=
3
> 2022-12-28-11-25-38:  140       267899   IR-PCI-MSI 13117447-edge      vm=
d1
> 2022-12-28-11-25-38:  183       265978   IR-PCI-MSI 13117490-edge      vm=
d1
> ......
> 2022-12-28-11-25-42: irqtop - IRQ : 2109, TOTAL : 2377172002, CPU :
> 192, ACTIVE CPU : 192
>
> From the result it is not difficult to find, in remapping mode the
> interruptions come from vmd.
> While in other modes, interrupts come from nvme devices. Besides, we
> found the port mounting
> 4 dirves total interruptions is much fewer than the port mounting 2 or 1 =
drive.
> NVME 8 and 9 mount in one port, other port mount 4 dirves.
>
> 2022-12-28-11-39-14: 2582       494635   IR-PCI-MSI 470810698-edge      n=
vme9q74
> 2022-12-28-11-39-14: 2579       489972   IR-PCI-MSI 470810697-edge      n=
vme9q73
> 2022-12-28-11-39-14: 2573       480024   IR-PCI-MSI 470810695-edge      n=
vme9q71
> 2022-12-28-11-39-14: 2544       312967   IR-PCI-MSI 470286401-edge      n=
vme8q65
> 2022-12-28-11-39-14: 2556       312229   IR-PCI-MSI 470286405-edge      n=
vme8q69
> 2022-12-28-11-39-14: 2547       310013   IR-PCI-MSI 470286402-edge      n=
vme8q66
> 2022-12-28-11-39-14: 2550       308993   IR-PCI-MSI 470286403-edge      n=
vme8q67
> 2022-12-28-11-39-14: 2559       308794   IR-PCI-MSI 470286406-edge      n=
vme8q70
> ......
> 2022-12-28-11-39-14: 1296       185773   IR-PCI-MSI 202375243-edge      n=
vme1q75
> 2022-12-28-11-39-14: 1209       185646   IR-PCI-MSI 201850947-edge      n=
vme0q67
> 2022-12-28-11-39-14: 1831       184151   IR-PCI-MSI 203423828-edge      n=
vme3q84
> 2022-12-28-11-39-14: 1254       182313   IR-PCI-MSI 201850950-edge      n=
vme0q70
> 2022-12-28-11-39-14: 1224       181665   IR-PCI-MSI 201850948-edge      n=
vme0q68
> 2022-12-28-11-39-14: 1179       180115   IR-PCI-MSI 201850945-edge      n=
vme0q65
> > I'd vote for it being in VMD mode (non-bypass) by default.
> I speculate that the vmd controller equalizes the interrupt load and
> acts like a buffer,
> which improves the performance of nvme. I am not sure about my
> analysis. So, I'd like
> to discuss it with the community.