My dd vs load non-cached binary woes seem to be coming from backmerge.
#if 0 /*MIKEDIDIT sand in gearbox?*/
/*
* See if our hash lookup can find a potential backmerge.
*/
__rq = elv_rqhash_find(q, bio->bi_sector);
if (__rq && elv_rq_merge_ok(__rq, bio)) {
*req = __rq;
return ELEVATOR_BACK_MERGE;
}
#endif
- = stock = 0
+ = /sys/block/sdb/queue/nomerges = 1
x = backmerge disabled
quantum = 1 Avg
dd pre 58.4 52.5 56.1 61.6 52.3 56.1- MB/s
virgin/foo
59.6 54.4 53.0 56.1 58.6 56.3+
1.003
53.8 56.6 54.7 50.7 59.3 55.0x
.980
perf stat 2.87 0.91 1.64 1.41 0.90 1.5- Sec
2.61 1.14 1.45 1.43 1.47 1.6+
1.066
1.07 1.19 1.20 1.24 1.37 1.2x
.800
dd post 56.6 61.0 66.3 64.7 60.9 61.9-
54.0 59.3 61.1 58.3 58.9 58.3+
.941
54.3 60.2 59.6 60.6 60.3 59.0x
.953
quantum = 2
dd pre 59.7 62.4 58.9 65.3 60.3 61.3-
49.4 51.9 58.7 49.3 52.4 52.3+
.853
58.3 52.8 53.1 50.4 59.9 54.9x
.895
perf stat 5.81 6.09 6.24 10.13 6.21 6.8-
2.48 2.10 3.23 2.29 2.31 2.4+
.352
2.09 2.73 1.72 1.96 1.83 2.0x
.294
dd post 64.0 62.6 64.2 60.4 61.1 62.4-
52.9 56.2 49.6 51.3 51.2 52.2+
.836
54.7 60.9 56.0 54.0 55.4 56.2x
.900
quantum = 3
dd pre 65.5 57.7 54.5 51.1 56.3 57.0-
58.1 53.9 52.2 58.2 51.8 54.8+
.961
60.5 56.5 56.7 55.3 54.6 56.7x
.994
perf stat 14.01 13.71 8.35 5.35 8.57 9.9-
1.84 2.30 2.14 2.10 2.45 2.1+
.212
2.12 1.63 2.54 2.23 2.29 2.1x
.212
dd post 59.2 49.1 58.8 62.3 62.1 58.3-
59.8 53.2 55.2 50.9 53.7 54.5+
.934
56.1 61.9 51.9 54.3 53.1 55.4x
.950
quantun = 4
dd pre 57.2 52.1 56.8 55.2 61.6 56.5-
48.7 55.4 51.3 49.7 54.5 51.9+
.918
55.8 54.5 50.3 56.4 49.3 53.2x
.941
perf stat 11.98 1.61 9.63 16.21 11.13 10.1-
2.29 1.94 2.68 2.46 2.45 2.3+
.227
3.01 1.84 2.11 2.27 2.30 2.3x
.227
dd post 57.2 52.6 62.2 49.3 50.2 54.3-
50.1 54.5 58.4 54.1 49.0 53.2+
.979
52.9 53.2 50.6 53.2 50.5 52.0x
.957
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