On 30/06/2021 01:32, Ming Lei wrote:
Many block drivers don't use managed interrupts - to be proper, why not set
this everywhere (which doesn't use managed interrupts)? I know why, but it's
odd.
It is just one small optimization in slow path for other drivers, not sure these
drivers are interested in such change. It only serves as fix for callers of
blk_mq_alloc_request_hctx().
Anyway, we can document the situation.
As an alternative, if the default queue mapping was used (in
blk_mq_map_queues()), then that's the same thing as
BLK_MQ_F_NOT_USE_MANAGED_IRQ in reality, right? If so, could we
alternatively check for that somehow?
This way can't work, for example of NVMe PCI, managed irq is used for
the default/write queues, but poll queues uses blk_mq_map_queues().
Also it can't cover all cases, such as MVMe RDMA.
Using managed irq or not is thing of driver's choice, and not sure if it
is good for block layer to provide such abstract. I'd suggest to fix the
issue still by passing one flag, given we needn't it everywhere so far.
Sure, but I am just trying to suggest a more automatic way of passing
this info. Like, for example, if we use blk_mq_pci_map_queues() on the
qmap, then you prob want blk-mq managed interrupt support (for that
qmap), i.e. CPU hotplug handlers.
Thanks,
John
