On 11/15/19 7:21 AM, Pavel Begunkov wrote: > On 15/11/2019 12:40, Pavel Begunkov wrote: >>>> Finally got to this patch. I think, find it adding too many edge cases >>>> and it isn't integrated consistently into what we have now. I would love >>>> to hear your vision, but I'd try to implement them in such a way, that it >>>> doesn't need to modify the framework, at least for some particular case. >>>> In other words, as opcodes could have been added from the outside with a >>>> function table. >>> >>> I agree, it could do with a bit of cleanup. Incrementals would be >>> appreciated! >>> >>>> Also, it's not so consistent with the userspace API as well. >>>> >>>> 1. If we specified drain for the timeout, should its start be delayed >>>> until then? I would prefer so. >>>> >>>> E.g. send_msg + drained linked_timeout, which would set a timeout from the >>>> start of the send. >>> >>> What cases would that apply to, what would the timeout even do in this >>> case? The point of the linked timeout is to abort the previous command. >>> Maybe I'm not following what you mean here. >>> >> Hmm, got it a bit wrong with defer. io_queue_link_head() can defer it >> without setting timeout. However, it seems that io_wq_submit_work() >> won't set a timer, as it uses __io_submit_sqe(), but not >> __io_queue_sqe(), which handles all this with linked timeouts. >> >> Indeed, maybe it be, that you wanted to place it in __io_submit_sqe? >> >>>> 2. Why it could be only the second one in a link? May we want to cancel >>>> from a certain point? >>>> e.g. "op1 -> op2 -> timeout -> op3" cancels op2 and op3 >>> >>> Logically it need not be the second, it just has to follow another >>> request. Is there a bug there? >>> >> __io_queue_sqe looks only for the second one in a link. Other linked >> timeouts will be ignored, if I get the code right. >> >> Also linking may (or __may not__) be an issue. As you remember, the head >> is linked through link_list, and all following with list. >> i.e. req_head.link_list <-> req.list <-> req.list <-> req.list >> >> free_req() (last time I saw it), expects that timeout's previous request >> is linked with link_list. If a timeout can fire in the middle of a link >> (during execution), this could be not the case. But it depends on when >> we set an timeout. >> >> BTW, personally I'd link them all through link_list. E.g. may get rid of >> splicing in free_req(). I'll try to make it later. >> >>>> 3. It's a bit strange, that the timeout affects a request from the left, >>>> and after as an consequence cancels everything on the right (i.e. chain). >>>> Could we place it in the head? So it would affect all requests on the right >>>> from it. >>> >>> But that's how links work, though. If you keep linking, then everything >>> that depends on X will fail, if X itself isn't succesful. >>> >> Right. That's about what userspace API would be saner. To place timeout >> on the left of a request, or on the right, with the same resulting effect. >> >> Let put this question away until the others are clear. >> >>>> 4. I'd prefer to handle it as a new generic command and setting a timer >>>> in __io_submit_sqe(). >>>> >>>> I believe we can do it more gracefully, and at the same moment giving >>>> more freedom to the user. What do you think? >>> >>> I just think we need to make sure the ground rules are sane. I'm going >>> to write a few test cases to make sure we do the right thing. >>> >> > Ok, let me try to state some rules to discuss: > 1. REQ -> LINK_TIMEOUT > is a valid use case Yes > 2. timeout is set at the moment of starting execution of operation. > e.g. REQ1, REQ2|DRAIN -> LINK_TIMEOUT > > Timer is set at the moment, when everything is drained and we > sending REQ. i.e. after completion of REQ1 Right, the timeout is prepped before REQ2 is started, armed when it is started (if not already done). The prep + arm split is important to ensure that a short timeout doesn't even find REQ2. > 3. REQ1 -> LINK_TIMEOUT1 -> REQ2 -> LINK_TIMEOUT2 > > is valid, and LINK_TIMEOUT2 will be set, at the moment of > start of REQ2's execution. It also mean, that if > LINK_TIMEOUT1 fires, it will cancel REQ1, and REQ2 > with LINK_TIMEOUT2 (with proper return values) That's not valid with the patches I sent. It could be, but we'd need to fix that bit. > 4. REQ1, LINK_TIMEOUT > is invalid, fail it Correct > 5. LINK_TIMEOUT1 -> LINK_TIMEOUT2 > Fail first, link-fail (aka cancelled) for the second one Correct > 6. REQ1 -> LINK_TIMEOUT1 -> LINK_TIMEOUT2 > execute REQ1+LINK_TIMEOUT1, and then fail LINK_TIMEOUT2 as > invalid. Also, LINK_TIMEOUT2 could be just cancelled > (e.g. if fail_links for REQ1) Given case 5, why would this one be legal? -- Jens Axboe
