blk-mq and interrupt affinity

blk-mq and interrupt affinity

[Hannes Reinecke]

Hi all,

Looking through the blk-mq code I tried to figure out if and how the
driver is supposed to set any interrupt affinity when block-mq is
enabled.

Thing is, for your typical driver you would set the interrupt
affinity during init time (eg for SCSI drivers during host_alloc).
But to set the interrupt affinity you'd need the cpumask, which is
only populated way later during queue setup.

So now I got two bad choices: either I have to delay setting the
interrupt affinity until after the queue is created, making things
awkward with several queues, or I have to out-guess the blk-mq
mapping algorithm and set the interrupt affinity prior to queue setup.

Tests with the lpfc driver found that one absolutely _does_ want to
do irq affinity; not doing so limits the performance to single-queue
results.

So what is the expected strategy here?
Or am I just too stupid to find it?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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