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

[Hannes Reinecke <hare@suse.de>]

On 4/28/26 14:53, Daniel Wagner wrote:
> On Mon, Apr 27, 2026 at 05:34:16PM +0200, Sebastian Andrzej Siewior wrote:
>> 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).
> 
> These HBAs are used on PowerPC which supports lpar (CPUs can be added
> during runtime) I am told it's properly the only driver which is caring
> about this type configuration, thus a bit of an odd ball.
> 
>> In case cpu_possible_mask != cpu_online_mask the intention is to
>> allocate memory and setup irqs for the offline CPUs?
> 
> I can't answer this. The lpfc driver has several strategies implemented
> how it spreads its resources.

The intention is to setup the driver queue affinity only once (knowing 
that all possible CPUs are handled correctly), avoiding a driver
reconfiguration on CPU hotplug.

Not the most efficient one, sure.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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