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. Adding Pavel and Yi Zhang. -- Jens Axboe
