linux-kernel - Re: [RFC PATCH v2] blk-mq: Introduce per sw queue time-slice

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Date:	Mon, 1 Feb 2016 23:46:34 +0100
From:	Andreas Herrmann <aherrmann@...e.com>
To:	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org,
	Johannes Thumshirn <jthumshirn@...e.de>,
	Jan Kara <jack@...e.cz>
Subject: Re: [RFC PATCH v2] blk-mq: Introduce per sw queue time-slice

Following benchmark results for the patch using fio.

 - kernel version 4.5.0-rc2-0001 (ie. with time-slice patch) 
 - Intel Core i7-3770S CPU @ 3.10GHz system, 4 cores, 8 threads/CPUs
 - fio version as of 2.2.9-37-g0e1c4
 - results were gathered iterating using rw and numjobs parameter, e.g.:

    fio --directory=$1 --rw=$j --name=fio-scaling --size=5G --group_reporting \
        --ioengine=libaio --direct=1 --iodepth=1 --runtime=$2 --numjobs=$i

 - rotational device was a 1500GB Samsung HD155UI

    ata3.00: ATA-8: SAMSUNG HD155UI, 1AQ10001, max UDMA/133
    scsi 2:0:0:0: Direct-Access     ATA      SAMSUNG HD155UI  0001 PQ: 0 ANSI: 5

 - no regression between blk-mq using vanilla v4.5-rc2 kernel and new
   blk-mq w/ time_slice_us=0
 - I omitted random read/write/rw tests as there was no significant
   difference
 - time_slice_us=250 seems to be optimal choice
   (I compared 1000 µs, 500 µs, 250 µs and 50 µs)

 (1) cfq, slice_idle=8 (default)
 (2) cfq, slice_idle=0
 (3) blk-mq, time_slice_us=0 (behaviour matches unmodified mainline) 
 (4) blk-mq, time_slice_us=250  (250 µs) (time slice incremented)

 ---------------------------------------------------------------------
 n       cfq              cfq            blk-mq           blk-mq
 u       (1)              (2)              (3)              (4) 
 m
 j                                           0              250 
 o                                          µs               µs 
 b
 s
 ---------------------------------------------------------------------
                        read iops [mean (stdev)]
 ---------------------------------------------------------------------
 1 17394.6 (470.48) 17336.4 (382.88) 20324.5 ( 72.75) 18914.5 (324.23)
 2 15862.1 (416.38)  8427.8 (104.45)  8373.2 ( 71.97) 13216.6 (964.83)
 3 16597.1 (246.77)  7078.0 (107.29)  8671.3 (238.12) 12370.2 (276.76)
 4 15078.6 (132.34)  8589.8 (169.00)  9107.5 (328.00) 11582.0 (225.09)
 5 14392.2 ( 75.55)  5908.5 (120.76)  6052.0 (102.01) 10906.3 (435.44)
 6 13540.2 (142.83)  5902.9 (122.41)  5944.5 ( 90.23)  9758.9 (374.65)
 7 13112.4 (175.02)  5938.7 ( 99.70)  5982.2 (104.44)  9233.0 (616.16)
 8 12651.0 (187.11)  5955.9 (181.99)  6010.2 (105.62)  8908.5 (399.25)
 ---------------------------------------------------------------------
                        write iops [mean (stdev)]
 ---------------------------------------------------------------------
 1 15233.6 (236.28) 15062.4 (176.56) 17141.0 (107.48  16236.8 (128.94)
 2 15333.5 (474.39)  9860.1 ( 58.42) 10020.0 ( 38.67  15027.4 (288.07)
 3 15753.6 (459.48)  9552.5 (153.48)  9523.0 (111.82  14021.5 (551.12)
 4 15932.2 (328.94)  9949.8 ( 97.03)  9946.0 (110.38  13166.0 (289.70)
 5 15840.5 (407.32)  9886.9 ( 43.84)  9814.0 ( 60.92  12401.2 (706.76)
 6 16071.2 (349.90)  9822.1 ( 88.81)  9796.0 ( 83.29  11916.1 (904.20)
 7 15864.1 (353.14)  9684.6 ( 63.48)  9628.0 ( 35.54  12194.0 (292.25)
 8 15901.2 (308.38)  9474.3 ( 86.85)  9447.0 ( 40.46  11933.3 (633.21)                
 ---------------------------------------------------------------------
                        rw (read) iops [mean (stdev)]
 ---------------------------------------------------------------------
 1  4034.5 ( 76.29)  4238.7 ( 65.71)  4305.9 (107.76)  4069.8 (115.45)
 2  3727.7 (108.46)  3860.5 (274.02)  4194.4 (132.19)  3909.3 (202.47)
 3  3837.6 ( 57.84)  3533.6 (206.67)  3560.5 (145.49)  3625.9 (170.29)
 4  3650.8 ( 53.90)  3201.1 ( 72.26)  3123.0 (154.18)  3506.5 (142.67)
 5  3638.8 (102.67)  3043.1 (122.89)  3210.6 ( 89.05)  3301.1 (194.63)
 6  3592.9 ( 93.41)  3002.3 (114.94)  3180.3 ( 42.36)  3297.5 (200.37)
 7  3666.1 ( 66.77)  3081.3 ( 92.76)  3120.7 (127.99)  3210.4 (139.00)                 
 8  3787.5 ( 46.90)  2859.6 (220.61)  2978.1 (119.55)  3215.4 (166.90)                 
 ---------------------------------------------------------------------
                        rw (write) iops [mean (stdev)]
 ---------------------------------------------------------------------
 1  4037.4 ( 74.32)  4241.1 ( 66.48)  4306.4 (105.00)  4073.3 (115.22)
 2  3740.1 (102.04)  3868.2 (265.28)  4193.9 (128.23)  3914.6 (195.13)
 3  3832.9 ( 58.52)  3526.3 (209.27)  3550.3 (148.23)  3622.4 (169.52)
 4  3647.1 ( 53.76)  3211.4 ( 68.84)  3133.7 (152.57)  3504.2 (138.19)
 5  3642.5 (102.65)  3051.0 (114.87)  3206.6 ( 84.58)  3303.5 (193.98)
 6  3610.2 ( 93.48)  3013.7 (124.22)  3208.8 ( 45.25)  3291.2 (197.91)
 7  3681.6 ( 66.38)  3077.4 ( 91.72)  3118.5 (130.27)  3184.9 (140.03)
 8  3792.6 ( 49.89)  2816.7 (235.14)  2943.7 (133.80)  3176.4 (164.24)
 ---------------------------------------------------------------------