[ltt-dev] [RFC PATCH] block: Fix bio merge induced high I/O latency

[KOSAKI Motohiro]

> So, I ran the tests with my corrected patch, and the results are very
> good !
> 
> "incoming ssh connexion" test
> 
> "config 2.6.28 cfq"
> Linux 2.6.28
> /sys/block/sd{a,b}/device/queue_depth = 31 (default)
> /sys/block/sd{a,b}/queue/iosched/slice_async_rq = 2 (default)
> /sys/block/sd{a,b}/queue/iosched/quantum = 4 (default)
> 
> "config 2.6.28.1-patch1"
> Linux 2.6.28.1
> Corrected cfq patch applied
> echo 1 > /sys/block/sd{a,b}/device/queue_depth
> echo 1 > /sys/block/sd{a,b}/queue/iosched/slice_async_rq
> echo 1 > /sys/block/sd{a,b}/queue/iosched/quantum
> 
> On /dev/sda :
> 
> I/O scheduler        runt-min (msec)   runt-max (msec)
> cfq (2.6.28 cfq)          523             6637
> cfq (2.6.28.1-patch1)     579             2082
> 
> On raid1 :
> 
> I/O scheduler        runt-min (msec)   runt-max (msec)
> cfq (2.6.28 cfq)           523            28216
> cfq (2.6.28.1-patch1)      517             3086

Congraturation.
In university machine room (at least, the university in japan), 
parallel ssh workload freqently happend.

I like this patch :)



> 
> It looks like we are getting somewhere :) Are there any specific
> queue_depth, slice_async_rq, quantum variations you would like to be
> tested ?
> 
> For reference, I attach my ssh-like job file (again) to this mail.
> 
> Mathieu
> 
> 
> [job1]
> rw=write
> size=10240m
> direct=0
> blocksize=1024k
> 
> [global]
> rw=randread
> size=2048k
> filesize=30m
> direct=0
> bsrange=4k-44k
> 
> [file1]
> startdelay=0
> 
> [file2]
> startdelay=4
> 
> [file3]
> startdelay=8
> 
> [file4]
> startdelay=12
> 
> [file5]
> startdelay=16
> 
> [file6]
> startdelay=20
> 
> [file7]
> startdelay=24
> 
> [file8]
> startdelay=28
> 
> [file9]
> startdelay=32
> 
> [file10]
> startdelay=36
> 
> [file11]
> startdelay=40
> 
> [file12]
> startdelay=44
> 
> [file13]
> startdelay=48
> 
> [file14]
> startdelay=52
> 
> [file15]
> startdelay=56
> 
> [file16]
> startdelay=60
> 
> [file17]
> startdelay=64
> 
> [file18]
> startdelay=68
> 
> [file19]
> startdelay=72
> 
> [file20]
> startdelay=76
> 
> [file21]
> startdelay=80
> 
> [file22]
> startdelay=84
> 
> [file23]
> startdelay=88
> 
> [file24]
> startdelay=92
> 
> [file25]
> startdelay=96
> 
> [file26]
> startdelay=100
> 
> [file27]
> startdelay=104
> 
> [file28]
> startdelay=108
> 
> [file29]
> startdelay=112
> 
> [file30]
> startdelay=116
> 
> [file31]
> startdelay=120
> 
> [file32]
> startdelay=124
> 
> [file33]
> startdelay=128
> 
> [file34]
> startdelay=132
> 
> [file35]
> startdelay=134
> 
> [file36]
> startdelay=138
> 
> [file37]
> startdelay=142
> 
> [file38]
> startdelay=146
> 
> [file39]
> startdelay=150
> 
> [file40]
> startdelay=200
> 
> [file41]
> startdelay=260
> 
> -- 
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
> 
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