On Tue, May 19, 2015 at 1:55 PM, Tahsin Erdogan <[email protected]> wrote: > CFQ idling causes reduced IOPS throughput on non-rotational disks. > Since disk head seeking is not applicable to SSDs, it doesn't really > help performance by anticipating future near-by IO requests. > > By turning off idling (and switching to IOPS mode), we allow other > processes to dispatch IO requests down to the driver and so increase IO > throughput. > > Following FIO benchmark results were taken on a cloud SSD offering with > idling on and off: > > Idling iops avg-lat(ms) stddev bw > ------------------------------------------------------ > On 7054 90.107 38.697 28217KB/s > Off 29255 21.836 11.730 117022KB/s > > fio --name=temp --size=100G --time_based --ioengine=libaio \ > --randrepeat=0 --direct=1 --invalidate=1 --verify=0 \ > --verify_fatal=0 --rw=randread --blocksize=4k --group_reporting=1 \ > --filename=/dev/sdb --runtime=10 --iodepth=64 --numjobs=10 > > And the following is from a local SSD run: > > Idling iops avg-lat(ms) stddev bw > ------------------------------------------------------ > On 19320 33.043 14.068 77281KB/s > Off 21626 29.465 12.662 86507KB/s > > fio --name=temp --size=5G --time_based --ioengine=libaio \ > --randrepeat=0 --direct=1 --invalidate=1 --verify=0 \ > --verify_fatal=0 --rw=randread --blocksize=4k --group_reporting=1 \ > --filename=/fio_data --runtime=10 --iodepth=64 --numjobs=10 > > Reviewed-by: Nauman Rafique <[email protected]> > Signed-off-by: Tahsin Erdogan <[email protected]> > --- > block/cfq-iosched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 5da8e6e..402be01 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -4460,7 +4460,7 @@ static int cfq_init_queue(struct request_queue *q, > struct elevator_type *e) > cfqd->cfq_slice[1] = cfq_slice_sync; > cfqd->cfq_target_latency = cfq_target_latency; > cfqd->cfq_slice_async_rq = cfq_slice_async_rq; > - cfqd->cfq_slice_idle = cfq_slice_idle; > + cfqd->cfq_slice_idle = blk_queue_nonrot(q) ? 0 : cfq_slice_idle; > cfqd->cfq_group_idle = cfq_group_idle; > cfqd->cfq_latency = 1; > cfqd->hw_tag = -1; > -- > 2.2.0.rc0.207.ga3a616c >
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