[PATCH] nvme-pci: do not set the NUMA node of device if it has none

[Keith Busch]

On Tue, Jul 25, 2023 at 01:06:22PM +0200, Pratyush Yadav wrote:
> If a device has no NUMA node information associated with it, the driver
> puts the device in node first_memory_node (say node 0). As a side
> effect, this gives an indication to userspace IRQ balancing programs
> that the device is in node 0 so they prefer CPUs in node 0 to handle the
> IRQs associated with the queues. For example, irqbalance will only let
> CPUs in node 0 handle the interrupts. This reduces random access
> performance on CPUs in node 1 since the interrupt for command completion
> will fire on node 0.
>
> For example, AWS EC2's i3.16xlarge instance does not expose NUMA
> information for the NVMe devices. This means all NVMe devices have
> NUMA_NO_NODE by default. Without this patch, random 4k read performance
> measured via fio on CPUs from node 1 (around 165k IOPS) is almost 50%
> less than CPUs from node 0 (around 315k IOPS). With this patch, CPUs on
> both nodes get similar performance (around 315k IOPS).

irqbalance doesn't work with this driver though: the interrupts are
managed by the kernel. Is there some other reason to explain the perf
difference?