Make sched_random() return an unsigned number.

[imp]

Summary

Make sched_random() return an unsigned number, and use uint32_t
consistently. This also matches the per-cpu pointer declaration
anyway.

This changes the tweak we give to the load from -32..31 to be 0..63
which seems more inline with the rest of the code (- rnd and the -=
64). It should also provide the randomness we need, and may fix a
signedness bug in the old code (it isn't clear that the effect was
intentional as opposed to sloppy, and the right shift of a signed
value is undefined).

[imp]

Only return upper 16 bits from sched_random() and just mask out what
we need.

[avg]

sys/kern/sched_ule.c

367 ↗

(On Diff #4018)

I think that the function name should be on a new line.

[bjk]

(inline)

sys/kern/sched_ule.c

722 ↗

(On Diff #4018)

It is rather unusual to specify a bitmask as a decimal constant; 0x1f might be more clear.
I think this only returns a value in [0, 31], too, whereas the comment in the previous code says negative values are also possible.

[imp]

In D1981#9, @bjk wrote:

(inline)

It's not clear that was intentional. It relied on undefined behavior to make it happen if it did. It could also
make some of the invariants wrong if it subtracted a negative number. I think it was just sloppiness in the
original implementation rather than something intentional.

I've change it to % 32, since that's what we really want and there's no constant for the 64 that's
based on.

[imp]

sys/kern/sched_ule.c

367 ↗

(On Diff #4018)

Yup. Had to make other changes, so this goes in too.

[imp]

Nits

[imp]

Closed by commit rS279373 (authored by @imp).