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

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Date:   Tue, 25 Jul 2023 08:35:18 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Pratyush Yadav <ptyadav@...zon.de>
Cc:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: do not set the NUMA node of device if it has
 none

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?