Re: [PATCH] : Revert "ACPI: Remove side effect of partly creating a node in acpi_get_node()"

[Jonathan Lemon <jonathan.lemon@gmail.com>]

On 12 May 2022, at 3:15, Jonathan Cameron wrote:

> On Wed, 11 May 2022 19:44:14 +0200
> "Rafael J. Wysocki" <rafael@kernel.org> wrote:
>
>> On Wed, May 11, 2022 at 7:42 PM Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>>>
>>> On 11 May 2022, at 10:33, Rafael J. Wysocki wrote:
>>>
>>>> On Wed, May 11, 2022 at 7:24 PM Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>>>>>
>>>>> This reverts commit a62d07e0006a3a3ce77041ca07f3c488ec880790.
>>>>>
>>>>> The change calls pxm_to_node(), which ends up returning -1
>>>>> (NUMA_NO_NODE) on some systems for the pci bus, as opposed
>>>>> to the prior call to acpi_map_pxm_to_node(), which returns 0.
>>>>>
>>>>> The default numa node is then inherited by all pci devices, and is
>>>>> visible in /sys/bus/pci/devices/*/numa_node
>>>>>
>>>>> The prior behavior shows:
>>>>>  # cat /sys/bus/pci/devices/*/numa_node | sort | uniq -c
>>>>>      122 0
>>>>>
>>>>> While the new behavior has:
>>>>>  # cat /sys/bus/pci/devices/*/numa_node | sort | uniq -c
>>>>>        1 0
>
> Curious, which device is turning up in node 0?

Oddly enough, the NVME drive:

01:00.0 Non-Volatile memory controller: SK hynix PC401 NVMe Solid State Drive 256GB (prog-if 02 [NVM Express])
        Subsystem: SK hynix PC401 NVMe Solid State Drive 256GB
        NUMA node: 0

These are single-socket Skylake DE platforms.


>>>>>
>>>>> While arguably NUMA_NO_NODE is correct on single-socket systems which
>>>>> have only one numa domain, this breaks scripts that attempt to read the
>>>>> NIC numa_node and pass that to numactl in order to pin memory allocation
>>>>> when running applications (like iperf).  E.g.:
>>>>>
>>>>>   # numactl -p -1 iperf3
>>>>>   libnuma: Warning: node argument -1 is out of range
>>>>>   <-1> is invalid
>>>>>
>>>>> Reverting this change restores the prior behavior.
>>>>
>>>> Well, that's not a recent commit and it fixed a real and serious issue.
>>>>
>>>> Isn't there a way to fix this other than reverting it?
>>>
>>> The userspace behavior changed - is there another way to fix things
>>> so that a valid numa_node is returned?
>>
>> Well, that's my question.

This also could be a BIOS issue that wasn’t noticed until the platforms were
updated to a newer kernel.
—
Jonathan


> As Rafael noted, we don't want to change the internal kernel representation because
> previous kernel behavior resulting in several paths where you could
> get NULL pointer de-references, but maybe we could special case
> it at the userspace boundary.
>
> e.g. override dev_to_node() return value here
> https://elixir.bootlin.com/linux/v5.18-rc6/source/drivers/pci/pci-sysfs.c#L358
>
> What's problematic is we missed this being being an issue until now and hence
> have shipping kernels with both behaviors.
>
> +CC Bjorn and linux-pci
>
> Jonathan