On Friday 2013-02-22 20:28, Martin Svec wrote: > > Yes, I've already tried the ROW scheduler. It helped for some low iodepths > depending on quantum settings but generally didn't solve the problem. I think > the key issue is that none of the schedulers can throttle I/O according to e.g. > average request roundtrip time. Shaohua Li is right here: > https://lkml.org/lkml/2012/12/11/598 -- as long as there's free room in > device's queue they blindly dispatch requests to it. > > Which is exactly what I see in deadline scheduler fifo queues: There're no read > requests to be scheduled between writes because all readers are starving. So > the scheduler keeps dispatching writes using all the remaining capacity of > device queue. Which in turn worses the read starvation. Bigger queue depth and > bigger writeback cache means higher chance for read starvation even from a > single writer. Sounds just like the bufferbloat problem in networking. Waiting for codel for the block layer :) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
