Re: [PATCH] nvme-tcp: align I/O cpu with blk-mq mapping

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 18, 2024 at 02:03:45PM +0200, Hannes Reinecke wrote:
> Add a new module parameter 'wq_affinity' to spread the I/O
> over all cpus within the blk-mq hctx mapping for the queue.
> This avoids bouncing I/O between cpus when we have less
> hardware queues than cpus.

What is the benefit when setting it?  What is the downside?  Why do you
think it needs to be conditional?

> +	}
>  	if (wq_unbound)
>  		queue->io_cpu = WORK_CPU_UNBOUND;
> +	else if (wq_affinity) {

Missing curly braces.  But this also means the wq_unbound options
is incompatible with your new one.

> +	} else
>  		queue->io_cpu = cpumask_next_wrap(n - 1, cpu_online_mask, -1, false);

Overly long line here.