Re: Deduplicate io_*_prep calls?

[Jens Axboe <axboe@kernel.dk>]

On 2/24/20 8:44 AM, Pavel Begunkov wrote:
>> Fine like this, though easier if you inline the patches so it's easier
>> to comment on them.
>>
>> Agree that the first patch looks fine, though I don't quite see why
>> you want to pass in opcode as a separate argument as it's always
>> req->opcode. Seeing it separate makes me a bit nervous, thinking that
>> someone is reading it again from the sqe, or maybe not passing in
>> the right opcode for the given request. So that seems fragile and it
>> should go away.
> 
> I suppose it's to hint a compiler, that opcode haven't been changed
> inside the first switch. And any compiler I used breaks analysis there
> pretty easy.  Optimising C is such a pain...

But if the choice is between confusion/fragility/performance vs obvious
and safe, then I'll go with the latter every time. We should definitely
not pass in req and opcode separately.

-- 
Jens Axboe