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 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 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) 4. REQ1, LINK_TIMEOUT is invalid, fail it 5. LINK_TIMEOUT1 -> LINK_TIMEOUT2 Fail first, link-fail (aka cancelled) for the second one 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) -- Pavel Begunkov
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