[PATCH] blk-mq: modify hybrid sleep time to aggressive

[Dongjoo Seo <commisori28@gmail.com>]

Current sleep time for hybrid polling is half of mean time.
The 'half' sleep time is good for minimizing the cpu utilization.
But, the problem is that its cpu utilization is still high.
this patch can help to minimize the cpu utilization side.

Below 1,2 is my test hardware sets.

1. Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz + Samsung 970 pro 1Tb
2. Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz + INTEL SSDPED1D480GA 480G

        |  Classic Polling | Hybrid Polling  | this Patch
-----------------------------------------------------------------
        cpu util | IOPS(k) | cpu util | IOPS | cpu util | IOPS  |
-----------------------------------------------------------------
1.       99.96   |   491   |  56.98   | 467  | 35.98    | 442   |
-----------------------------------------------------------------
2.       99.94   |   582   |  56.3    | 582  | 35.28    | 582   |

cpu util means that sum of sys and user util.

I used 4k rand read for this test.
because that case is worst case of I/O performance side.
below one is my fio setup.

name=pollTest
ioengine=pvsync2
hipri
direct=1
size=100%
randrepeat=0
time_based
ramp_time=0
norandommap
refill_buffers
log_avg_msec=1000
log_max_value=1
group_reporting
filename=/dev/nvme0n1
[rd_rnd_qd_1_4k_1w]
bs=4k
iodepth=32
numjobs=[num of cpus]
rw=randread
runtime=60
write_bw_log=bw_rd_rnd_qd_1_4k_1w
write_iops_log=iops_rd_rnd_qd_1_4k_1w
write_lat_log=lat_rd_rnd_qd_1_4k_1w

Thanks

Signed-off-by: Dongjoo Seo <commisori28@gmail.com>
---
 block/blk-mq.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1b25ec2fe9be..c3d578416899 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3749,8 +3749,7 @@ static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
 		return ret;
 
 	if (q->poll_stat[bucket].nr_samples)
-		ret = (q->poll_stat[bucket].mean + 1) / 2;
-
+		ret = (q->poll_stat[bucket].mean + 1) * 3 / 4;
 	return ret;
 }
 
-- 
2.17.1