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Date: Tue, 10 Jan 2023 20:28:54 +0800
From: Xinghui Li <korantwork@...il.com>
To: Jonathan Derrick <jonathan.derrick@...ux.dev>
Cc: Keith Busch <kbusch@...nel.org>, nirmal.patel@...ux.intel.com,
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
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.
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