Linux Virtualization - Jul 2020 - [PATCH 3/7] vhost_vdpa: implement IRQ offloading functions in vhost_vdpa

On 2020/7/15 ??5:20, Zhu, Lingshan wrote:
>>>>
>>>> I meant something like:
>>>>
>>>> unregister();
>>>> vq->call_ctx.producer.token = ctx;
>>>> register();
>>> This is what we are doing now, or I must missed somethig:
>>> if (ctx && ctx != token) {
>>> ????irq_bypass_unregister_producer(&vq->call_ctx.producer);
>>> ????vq->call_ctx.producer.token = ctx;
>>> ????irq_bypass_register_producer(&vq->call_ctx.producer);
>>>
>>> }
>>>
>>> It just unregister and register.
>>
>>
>> I meant there's probably no need for the check and another check
and
>> unregister before. The whole function is as simple as I suggested
above.
>>
>> Thanks
> IMHO we still need the checks, this function handles three cases:
> (1)if the ctx == token, we do nothing. For this unregister and register can
work, but waste of time.

But we have a more simple code and we don't care about the performance 
here since the operations is rare.

> (2)if token exists but ctx is NULL, this means user space issued an unbind,
so we need to only unregister the producer.

Note that the register/unregister have a graceful check of whether or 
not there's a token.

> (3)if ctx exists and ctx!=token, this means there is a new ctx, we need to
update producer by unregister and register.
>
> I think we can not simply handle all these cases by "unregister and
register".

So it looks to me the functions are equivalent.

Thanks

>
> Thanks,
> BR
> Zhu Lingshan