Re: [PATCH] PCI: vmd: Do not disable MSI-X remapping in VMD 28C0 controller

[Xinghui Li]

Friendly ping~

Xinghui Li <korantwork@xxxxxxxxx> 于2023年1月10日周二 20:28写道：
>
> Jonathan Derrick <jonathan.derrick@xxxxxxxxx> 于2023年1月10日周二 05:00写道：
> >
> > 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      nvme0q68
> 2022-12-28-11-39-14: 1179       180115   IR-PCI-MSI 201850945-edge      nvme0q65
> 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      nvme1q74
> 2022-12-28-12-05-56: 1701       168753   IR-PCI-MSI 14155849-edge      nvme1q73
> 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      vmd3
> 2022-12-28-11-25-38:  140       267899   IR-PCI-MSI 13117447-edge      vmd1
> 2022-12-28-11-25-38:  183       265978   IR-PCI-MSI 13117490-edge      vmd1
> ......
> 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      nvme9q74
> 2022-12-28-11-39-14: 2579       489972   IR-PCI-MSI 470810697-edge      nvme9q73
> 2022-12-28-11-39-14: 2573       480024   IR-PCI-MSI 470810695-edge      nvme9q71
> 2022-12-28-11-39-14: 2544       312967   IR-PCI-MSI 470286401-edge      nvme8q65
> 2022-12-28-11-39-14: 2556       312229   IR-PCI-MSI 470286405-edge      nvme8q69
> 2022-12-28-11-39-14: 2547       310013   IR-PCI-MSI 470286402-edge      nvme8q66
> 2022-12-28-11-39-14: 2550       308993   IR-PCI-MSI 470286403-edge      nvme8q67
> 2022-12-28-11-39-14: 2559       308794   IR-PCI-MSI 470286406-edge      nvme8q70
> ......
> 2022-12-28-11-39-14: 1296       185773   IR-PCI-MSI 202375243-edge      nvme1q75
> 2022-12-28-11-39-14: 1209       185646   IR-PCI-MSI 201850947-edge      nvme0q67
> 2022-12-28-11-39-14: 1831       184151   IR-PCI-MSI 203423828-edge      nvme3q84
> 2022-12-28-11-39-14: 1254       182313   IR-PCI-MSI 201850950-edge      nvme0q70
> 2022-12-28-11-39-14: 1224       181665   IR-PCI-MSI 201850948-edge      nvme0q68
> 2022-12-28-11-39-14: 1179       180115   IR-PCI-MSI 201850945-edge      nvme0q65
> > 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.