Hi, On 2020-12-11 01:44:38 +0000, Pavel Begunkov wrote: > In general the current hybrid polling doesn't work well with high QD, > that's because statistics it based on are not very resilient to all sorts > of problems. And it might be a problem I described long ago > > https://www.spinics.net/lists/linux-block/msg61479.html > https://lkml.org/lkml/2019/4/30/120 Interesting. > Are you interested in it just out of curiosity, or you have a good > use case? Modern SSDs are so fast that even with QD1 the sleep overhead > on sleeping getting considerable, all the more so for higher QD. It's a bit more than just idle curiosity, but not a strong need (yet). I was experimenting with using it for postgres WAL writes. The CPU cost of "classic" polling is high enough to make it not super attractive in a lot of cases. Often enough the QD is just 1 for data integrity writes on fast drives, but there's also cases (bulk load particularly, or high concurrency OLTP) where having multiple IOs in flight is important. > Because if there is no one who really cares, then instead of adding > elaborated correction schemes, I'd rather put max(time, 10ms) and > that's it. I wonder if it's doable to just switch from hybrid polling to classic polling if there's more than one request in flight? Greetings, Andres Freund
