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Subjectiosched: impact of streaming read on read-many-files

Here we look at what affect a large streaming read has upon an operation
which reads many small files from the same disk.

A single streaming read was set up with:

while true
do
cat 512M-file > /dev/null
done

and we measure how long it takes to read all the files from a 2.4.19 kernel
tree off the same disk with

time (find kernel-tree -type f | xargs cat > /dev/null)



2.4.21-pre4: 31 minutes 30 seconds

2.5.61+hacks: 3 minutes 39 seconds

2.5.61+CFQ: 5 minutes 7 seconds (*)

2.5.61+AS: 17 seconds





* CFQ performed very strangely here. Tremendous amount of seeking and a
big drop in aggregate bandwidth. See the vmstat 1 output from when the
kernel tree read started up:


r b swpd free buff cache si so bi bo in cs us sy id wa
0 1 1240 125260 1176 109488 0 0 40744 0 1672 725 0 3 49 47
0 1 1240 85892 1220 148788 0 0 39344 0 1651 693 0 3 49 48
0 1 1240 45124 1260 189492 0 0 40744 0 1663 683 0 3 49 47
1 1 1240 4544 1300 230068 0 0 40616 0 1661 837 0 4 49 47
0 2 1348 3468 944 231696 0 108 40488 148 1671 800 0 4 4 91
0 2 1348 2180 936 232920 0 0 40612 64 1668 789 0 4 0 96
0 3 1348 4220 996 230648 0 0 11348 0 1256 352 0 2 0 98
0 3 1348 4052 1064 230472 0 0 9012 0 1207 305 0 1 0 98
0 4 1348 3596 1148 230580 0 0 6756 0 1171 247 0 1 0 99
0 4 1348 4044 1148 229888 0 0 6344 0 1165 237 0 1 0 99
1 3 1348 3708 1160 230212 0 0 7800 0 1187 255 0 1 21 78


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