Hi
I think you should revert the patch
4c0ca26bd260dddf3b9781758cb5e2df3f74d4a3 that did this change:
for (f = 1; f < geo->far_copies; f++) {
d += geo->near_copies;
- if (d >= geo->raid_disks)
- d -= geo->raid_disks;
+ d %= geo->raid_disks;
s += geo->stride;
r10bio->devs[slot].devnum = d;
r10bio->devs[slot].addr = s;
On most processors, the divide and modulo operations are slower than a
possibly misprediteced branch or conditional move instruction.
So, replacing a condition with modulo doesn't make sense.
A benchmark on AMD K10 shows that mispredicted branch is 8.7 times faster
than a divide operation:
for (i = 0; i < 10000000; i++) {
q++;
if (q >= 8)
q -= 8;
}
- 11607us (it compiles to cmov and runs at a rate of 3 ticks per
iteration)
for (i = 0; i < 10000000; i++) {
q++;
q %= max;
}
- 101241us (26 ticks per iteration)
Mikulas
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