On Sun, Apr 12, 2020 at 5:15 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: > > On 4/12/2020 5:07 AM, Jens Axboe wrote: > > On 4/11/20 5:00 PM, Hrvoje Zeba wrote: > >> Hi, > >> > >> I've been looking at timeouts and found a case I can't wrap my head around. > >> > >> Basically, If you submit OPs in a certain order, timeout fires before > >> time elapses where I wouldn't expect it to. The order is as follows: > >> > >> poll(listen_socket, POLLIN) <- this never fires > >> nop(async) > >> timeout(1s, count=X) > >> > >> If you set X to anything but 0xffffffff/(unsigned)-1, the timeout does > >> not fire (at least not immediately). This is expected apart from maybe > >> setting X=1 which would potentially allow the timeout to fire if nop > >> executes after the timeout is setup. > >> > >> If you set it to 0xffffffff, it will always fire (at least on my > >> machine). Test program I'm using is attached. > >> > >> The funny thing is that, if you remove the poll, timeout will not fire. > >> > >> I'm using Linus' tree (v5.6-12604-gab6f762f0f53). > >> > >> Could anybody shine a bit of light here? > > > > Thinking about this, I think the mistake here is using the SQ side for > > the timeouts. Let's say you queue up N requests that are waiting, like > > the poll. Then you arm a timeout, it'll now be at N + count before it > > fires. We really should be using the CQ side for the timeouts. > > As I get it, the problem is that timeout(off=0xffffffff, 1s) fires > __immediately__ (i.e. not waiting 1s). Correct. > And still, the described behaviour is out of the definition. It's sounds > like int overflow. Ok, I'll debug it, rest assured. I already see a > couple of flaws anyway. For this particular case, req->sequence = ctx->cached_sq_head + count - 1; ends up being 1 which triggers in __req_need_defer() for nop sq. -- I doubt, therefore I might be.
