Re: [Lsf] [LSF/MM TOPIC] block-mq issues with FC

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>Hey Willy,
>
>>   - Interrupt steering needs to be controlled by block-mq instead of
>>     the driver.  It's pointless to have each driver implement its own
>>     policies on interrupt steering, irqbalanced remains a source of
>>     end-user frustration, and block-mq can change the queue<->cpu mapping
>>     without the driver's knowledge.
>
>I honestly don't think that block-mq is the right place to
>*assign* interrupt steering. Not all HW devices are dedicated
>to storage, take RDMA for example, a RNIC is shared by block
>storage, networking and even user-space workloads so obviously
>block-mq can't understand how a user wants to steer interrupts.
>
>I think that block-mq needs to ask the device driver:
>"what is the optimal queue index for cpu X?" and use it
>while *someone* will be responsible for optimum interrupt
>steering (can be the driver itself or user-space).

+0.5 on block-mq asking lower layer on where to place the queue.  However, I think it is better that the lower layer push up the data rather the block-mq asking for it.  User can change or irqbalance can relocate the interrupt vector(s) during runtime.  

For Qlogic adapter, it can act in both Initiator & Target Modes at the same time.  Certain target vendor might not wants the initiator side to holding this knob.




>
> From some discussions I had with HCH I think he intends to
>use the cpu reverse-mapping API to try and do what's described
>above (if I'm not mistaken).

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