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

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Date:   Mon, 6 Feb 2023 11:11:36 -0700
From:   "Patel, Nirmal" <nirmal.patel@...ux.intel.com>
To:     Xinghui Li <korantwork@...il.com>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>
Cc:     Keith Busch <kbusch@...nel.org>, lpieralisi@...nel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xinghui Li <korantli@...cent.com>
Subject: Re: [PATCH] PCI: vmd: Do not disable MSI-X remapping in VMD 28C0
 controller

On 2/6/2023 5:45 AM, Xinghui Li wrote:
> Friendly ping~
>
> Xinghui Li <korantwork@...il.com> 于2023年1月10日周二 20:28写道：
>> Jonathan Derrick <jonathan.derrick@...ux.dev> 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.

I like the idea of module parameter to allow switching between the modes
but keep MSI remapping enabled (non-bypass) by default.