cfq-iosched: Implment IOPS mode
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From: Jeff Moyer on 21 Jul 2010 16:40 Vivek Goyal <vgoyal(a)redhat.com> writes: > o Implement another CFQ mode where we charge queue/group in terms of number > of requests dispatched instead of measuring the time. Measuring in terms > of time is not possible when we are driving deeper queue depths and there > are requests from multiple cfq queues in the request queue. > > o This mode currently gets activated if one sets slice_idle=0 and associated > disk supports NCQ. Again the idea is that on an NCQ disk with idling disabled > most of the queues will dispatch 1 or more requests and then cfq queue > expiry happens and we don't have a way to measure time. So start providing > fairness in terms of IOPS. > > o Currently this primarily is beneficial with cfq group scheduling where one > can disable slice idling so that we don't idle on queue and drive deeper > request queue deptsh (achieving better throughput), at the same time group > idle is enabled so one should get service differentiation among groups. I like that this is more isolated now. I'm slowly warming up to it. I have one question--just a curiosity, really. What do you see now for the reported sl_used in blktrace when slice_idle is zero and the hardware supports command queueing? Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Vivek Goyal on 21 Jul 2010 17:00
On Wed, Jul 21, 2010 at 04:33:04PM -0400, Jeff Moyer wrote: > Vivek Goyal <vgoyal(a)redhat.com> writes: > > > o Implement another CFQ mode where we charge queue/group in terms of number > > of requests dispatched instead of measuring the time. Measuring in terms > > of time is not possible when we are driving deeper queue depths and there > > are requests from multiple cfq queues in the request queue. > > > > o This mode currently gets activated if one sets slice_idle=0 and associated > > disk supports NCQ. Again the idea is that on an NCQ disk with idling disabled > > most of the queues will dispatch 1 or more requests and then cfq queue > > expiry happens and we don't have a way to measure time. So start providing > > fairness in terms of IOPS. > > > > o Currently this primarily is beneficial with cfq group scheduling where one > > can disable slice idling so that we don't idle on queue and drive deeper > > request queue deptsh (achieving better throughput), at the same time group > > idle is enabled so one should get service differentiation among groups. > > I like that this is more isolated now. I'm slowly warming up to it. I > have one question--just a curiosity, really. What do you see now for > the reported sl_used in blktrace when slice_idle is zero and the > hardware supports command queueing? sl_used, still shows amount of time elapsed since we started dispatch from the queue. I retained that info because we export that info through cgroup interface. Just that charging logic to the group changed where in IOPS mode instead of charging sl_used, we charge iops. Following is sample output of blktrace after the patches. 253,0 0 0 0.014157613 0 m N cfq19226S /cgrp7 sl_used=3 disp=1 charge=1 iops=1 sect=8 Here we slice used since dispatch start is 3 jiffies, we dispatched 1 request in this duration. Because we are iops mode (iops=1), we charge the group for 1 rq and no 3 jiffies. (charge=1). sect shows we dispatched 8 sectors in this duration. Vivek > > Cheers, > Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |