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

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


A single streaming write was set up with:

while true
do
dd if=/dev/zero of=foo bs=1M count=512 conv=notrunc
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)

As a reference, the time to read the kernel tree with no competing I/O is 7.9
seconds.

2.4.21-pre4:

Don't know. I killed it after 15 minutes. Judging from the vmstat
output it would have taken many hours.

2.5.61+hacks: 7 minutes 27 seconds
r b swpd free buff cache si so bi bo in cs us sy id wa
0 8 0 2188 1200 226692 0 0 852 17664 1204 253 0 3 0 97
0 8 0 4148 1212 224804 0 0 1940 16208 1187 245 0 2 0 98
0 7 0 4260 1128 224756 0 0 324 20228 1226 298 0 3 0 97
0 8 0 4204 1048 224944 0 0 500 20856 1227 313 0 3 0 97
1 7 0 2300 1040 226840 0 0 348 20272 1227 313 0 3 0 97
0 8 0 4204 1044 224952 0 0 212 21564 1230 320 0 3 0 97

2.5.61+CFQ: 9 minutes 55 seconds
r b swpd free buff cache si so bi bo in cs us sy id wa
1 2 0 4308 1028 224660 0 0 180 38368 1250 357 0 3 6 91
0 4 0 2180 1020 226852 0 0 324 25196 1266 408 0 4 1 95
0 4 0 2236 1016 226744 0 0 252 26948 1276 449 0 4 2 93
0 4 0 4196 1020 224816 0 0 380 23204 1250 454 0 3 4 93
0 3 0 4356 1036 224632 0 0 2616 25824 1271 490 0 4 0 96
0 4 0 4140 968 224996 0 0 496 29416 1304 609 0 4 0 96
0 4 0 2180 948 226972 0 0 352 29364 1300 688 0 5 0 95
0 3 0 4364 928 224796 0 0 344 22100 1281 656 0 4 22 74

(CFQ had a strange 20-second pause in which it performed no reads at all)
(And a later 4-second one)
(then 10 seconds..)


2.5.61+AS: 17 seconds
r b swpd free buff cache si so bi bo in cs us sy id wa
0 6 0 2280 2716 226112 0 0 0 22388 1205 151 0 3 0 97
0 6 0 4296 2596 224168 0 0 0 21968 1213 148 0 3 0 97
1 6 0 3872 2516 224408 0 0 296 19552 1223 249 0 3 0 97
0 9 0 2176 2584 225324 0 0 5112 14588 1573 1424 0 5 0 94
0 8 0 3364 2668 223116 0 0 17512 8500 3059 6065 0 8 0 92
1 8 0 4156 2708 221340 0 0 12812 9560 2695 4863 0 9 0 91
0 8 0 3740 2956 221188 0 0 17216 7200 2406 4045 0 6 0 94
0 9 0 3828 2668 221192 0 0 9712 8972 1615 1540 0 5 0 94
1 6 0 2060 2924 222272 0 0 8428 17784 1713 1718 0 5 0 95


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