Re: Deduplicate io_*_prep calls?

[Pavel Begunkov <asml.silence@gmail.com>]

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On 24/02/2020 18:46, Jens Axboe wrote:
> 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.

Yep, and even better to go with the latter, and somehow hint, that it won't
change. Though, never found a way to do that. Have any tricks in a sleeve?


-- 
Pavel Begunkov


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