Re: [PATCH v12 05/13] blk-mq: add blk_mq_{online|possible}_queue_affinity

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-04-22 14:52:07 [-0400], Aaron Tomlin wrote:
> From: Daniel Wagner <wagi@kernel.org>
> 
> Introduce blk_mq_{online|possible}_queue_affinity, which returns the
> queue-to-CPU mapping constraints defined by the block layer. This allows
> other subsystems (e.g., IRQ affinity setup) to respect block layer
> requirements.
> 
> It is necessary to provide versions for both the online and possible CPU
> masks because some drivers want to spread their I/O queues only across
> online CPUs, while others prefer to use all possible CPUs. And the mask
> used needs to match with the number of queues requested
> (see blk_num_{online|possible}_queues).

Which driver uses cpu_possible_mask? This mask is assigned at boot time
once the kernel figured how many CPUs are possible based on ACPI or
whatever the system uses. This mask does not change.

I only see drivers/scsi/lpfc/lpfc_init.c using it. Looking at
cpu_possible_mask might not be the right thing. It is usually the same
thing as "online" except on system where ACPI thinks that something
could be added via hotplug _or_ if the admin shuts down a CPU via
cpuhotplug _or_ boots with less (there a command line option for that). 

In case cpu_possible_mask != cpu_online_mask the intention is to
allocate memory and setup irqs for the offline CPUs?

> Signed-off-by: Daniel Wagner <wagi@kernel.org>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>

Sebastian