linux-kernel - Re: Linux warns `Unknown NUMA node; performance will be reduced`

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Date: Tue, 18 Jun 2024 17:19:27 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
 Yunsheng Lin <linyunsheng@...wei.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: Linux warns `Unknown NUMA node; performance will be reduced`

[Cc: +X86 maintainers]


Dear Bjorn, dear Linux folks,


Am 11.06.24 um 17:11 schrieb Bjorn Helgaas:
> On Mon, Jun 10, 2024 at 10:27:37PM +0200, Paul Menzel wrote:
>> Am 10.06.24 um 21:42 schrieb Bjorn Helgaas:
>>> On Sun, Jun 09, 2024 at 10:31:05AM +0200, Paul Menzel wrote:
>>>> On the servers below Linux warns:
>>>>
>>>>        Unknown NUMA node; performance will be reduced
>>>
>>> This warning was added by ad5086108b9f ("PCI: Warn if no host bridge
>>> NUMA node info"), which appeared in v5.5, so I assume this isn't new.
>>>
>>> That commit log says:
>>>
>>>     In pci_call_probe(), we try to run driver probe functions on the node where
>>>     the device is attached.  If we don't know which node the device is attached
>>>     to, the driver will likely run on the wrong node.  This will still work,
>>>     but performance will not be as good as it could be.
>>>
>>>     On NUMA systems, warn if we don't know which node a PCI host bridge is
>>>     attached to.  This is likely an indication that ACPI didn't supply a _PXM
>>>     method or the DT didn't supply a "numa-node-id" property.
>>>
>>> I assume these are all ACPI systems, so likely missing _PXM.  An
>>> acpidump could confirm this.
>>
>> I created an issue in the Linux Kernel Bugzilla [1] and attached the output
>> of `acpidump` on a Dell PowerEdge T630 there. The DSDT contains:
>>
>>          Device (PCI1)
>>          {
>>          […]
>>              Method (_PXM, 0, NotSerialized)  // _PXM: Device Proximity
>>              {
>>                  If ((CLOD == 0x00))
>>                  {
>>                      Return (0x01)
>>                  }
>>                  Else
>>                  {
>>                      Return (0x02)
>>                  }
>>              }
>>          […]
>>          }
> 
> This machine (the T630, from your first message) has several PCI host
> bridges:
> 
>    ACPI: PCI Root Bridge [UNC1] (domain 0000 [bus ff])
>    pci_bus 0000:ff: root bus resource [bus ff]
> 
>    ACPI: PCI Root Bridge [UNC0] (domain 0000 [bus 7f])
>    pci_bus 0000:7f: root bus resource [bus 7f]
> 
>    ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-7e])
>    pci_bus 0000:00: root bus resource [io  0x0000-0x03bb window]
>    pci_bus 0000:00: root bus resource [io  0x03bc-0x03df window]
>    pci_bus 0000:00: root bus resource [io  0x03e0-0x0cf7 window]
>    pci_bus 0000:00: root bus resource [io  0x1000-0x7fff window]
>    pci_bus 0000:00: root bus resource [mem 0x000a0000-0x000bffff window]
>    pci_bus 0000:00: root bus resource [mem 0x90000000-0xc7ffbfff window]
>    pci_bus 0000:00: root bus resource [mem 0x38000000000-0x3bfffffffff window]
>    pci_bus 0000:00: root bus resource [bus 00-7e]
> 
>    ACPI: PCI Root Bridge [PCI1] (domain 0000 [bus 80-fe])
>    pci_bus 0000:80: root bus resource [io  0x8000-0xffff window]
>    pci_bus 0000:80: root bus resource [mem 0xc8000000-0xfbffbfff window]
>    pci_bus 0000:80: root bus resource [mem 0x3c000000000-0x3ffffffffff window]
>    pci_bus 0000:80: root bus resource [bus 80-fe]
> 
> PCI0 and PCI1 lead to all your normal PCI devices, they both
> implement _PXM, and they have all the usual apertures for PCI I/O and
> MMIO space where device BARs live.
> 
> UNC0 and UNC1 lead to these special chipset devices, they don't
> implement _PXM, and they don't have any resources except the bus
> number.  The devices on bus 7f and ff can only be used via config
> space accesses, and I have no idea what they are used for.

Maybe the X86 folks now.


Kind regards,

Paul


>> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=218951