Re: [PATCH v6 8/9] blk-mq: use hk cpus only when isolcpus=io_queue is enabled

[Ming Lei <ming.lei@redhat.com>]

On Thu, Apr 24, 2025 at 08:19:47PM +0200, Daniel Wagner wrote:
> When isolcpus=io_queue is enabled all hardware queues should run on
> the housekeeping CPUs only. Thus ignore the affinity mask provided by
> the driver. Also we can't use blk_mq_map_queues because it will map all
> CPUs to first hctx unless, the CPU is the same as the hctx has the
> affinity set to, e.g. 8 CPUs with isolcpus=io_queue,2-3,6-7 config
> 
>   queue mapping for /dev/nvme0n1
>         hctx0: default 2 3 4 6 7
>         hctx1: default 5
>         hctx2: default 0
>         hctx3: default 1
> 
>   PCI name is 00:05.0: nvme0n1
>         irq 57 affinity 0-1 effective 1 is_managed:0 nvme0q0
>         irq 58 affinity 4 effective 4 is_managed:1 nvme0q1
>         irq 59 affinity 5 effective 5 is_managed:1 nvme0q2
>         irq 60 affinity 0 effective 0 is_managed:1 nvme0q3
>         irq 61 affinity 1 effective 1 is_managed:1 nvme0q4
> 
> where as with blk_mq_hk_map_queues we get
> 
>   queue mapping for /dev/nvme0n1
>         hctx0: default 2 4
>         hctx1: default 3 5
>         hctx2: default 0 6
>         hctx3: default 1 7
> 
>   PCI name is 00:05.0: nvme0n1
>         irq 56 affinity 0-1 effective 1 is_managed:0 nvme0q0
>         irq 61 affinity 4 effective 4 is_managed:1 nvme0q1
>         irq 62 affinity 5 effective 5 is_managed:1 nvme0q2
>         irq 63 affinity 0 effective 0 is_managed:1 nvme0q3
>         irq 64 affinity 1 effective 1 is_managed:1 nvme0q4
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Daniel Wagner <wagi@kernel.org>
> ---
>  block/blk-mq-cpumap.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
> index 6e6b3e989a5676186b5a31296a1b94b7602f1542..2d678d1db2b5196fc2b2ce5678fdb0cb6bad26e0 100644
> --- a/block/blk-mq-cpumap.c
> +++ b/block/blk-mq-cpumap.c
> @@ -22,8 +22,8 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask,
>  {
>  	unsigned int num;
>  
> -	if (housekeeping_enabled(HK_TYPE_MANAGED_IRQ))
> -		mask = housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);
> +	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
> +		mask = housekeeping_cpumask(HK_TYPE_IO_QUEUE);

Here both two can be considered for figuring out nr_hw_queues:

	if (housekeeping_enabled(HK_TYPE_IO_QUEUE))
		mask = housekeeping_cpumask(HK_TYPE_IO_QUEUE);
	else if (housekeeping_enabled(HK_TYPE_MANAGED_IRQ))
		mask = housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);

>  
>  	num = cpumask_weight(mask);
>  	return min_not_zero(num, max_queues);
> @@ -61,11 +61,73 @@ unsigned int blk_mq_num_online_queues(unsigned int max_queues)
>  }
>  EXPORT_SYMBOL_GPL(blk_mq_num_online_queues);
>  
> +/*
> + * blk_mq_map_hk_queues - Create housekeeping CPU to hardware queue mapping
> + * @qmap:	CPU to hardware queue map
> + *
> + * Create a housekeeping CPU to hardware queue mapping in @qmap. If the
> + * isolcpus feature is enabled and blk_mq_map_hk_queues returns true,
> + * @qmap contains a valid configuration honoring the io_queue
> + * configuration. If the isolcpus feature is disabled this function
> + * returns false.
> + */
> +static bool blk_mq_map_hk_queues(struct blk_mq_queue_map *qmap)
> +{
> +	struct cpumask *hk_masks;
> +	cpumask_var_t isol_mask;
> +	unsigned int queue, cpu, nr_masks;
> +
> +	if (!housekeeping_enabled(HK_TYPE_IO_QUEUE))
> +		return false;

It could be more readable to move the above check to the caller.


Thanks, 
Ming