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sched: round a bit better 

round a tiny bit better in high-frequency rescheduling scenarios,
by rounding around zero instead of rounding down.

(this is pretty theoretical though)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2007-08-09 11:16:51 +02:00
parent 254753dc32
commit 194081ebfa
1 changed files with 11 additions and 7 deletions
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18
kernel/sched.c
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@ -638,6 +638,11 @@ static u64 div64_likely32(u64 divident, unsigned long divisor)
#define WMULT_SHIFT 32
/*
* Shift right and round:
*/
#define RSR(x, y) (((x) + (1UL << ((y) - 1))) >> (y))
static unsigned long
calc_delta_mine(unsigned long delta_exec, unsigned long weight,
struct load_weight *lw)
@ -645,18 +650,17 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
u64 tmp;
if (unlikely(!lw->inv_weight))
lw->inv_weight = WMULT_CONST / lw->weight;
lw->inv_weight = (WMULT_CONST - lw->weight/2) / lw->weight + 1;
tmp = (u64)delta_exec * weight;
/*
* Check whether we'd overflow the 64-bit multiplication:
*/
if (unlikely(tmp > WMULT_CONST)) {
tmp = ((tmp >> WMULT_SHIFT/2) * lw->inv_weight)
>> (WMULT_SHIFT/2);
} else {
tmp = (tmp * lw->inv_weight) >> WMULT_SHIFT;
}
if (unlikely(tmp > WMULT_CONST))
tmp = RSR(RSR(tmp, WMULT_SHIFT/2) * lw->inv_weight,
WMULT_SHIFT/2);
else
tmp = RSR(tmp * lw->inv_weight, WMULT_SHIFT);
return (unsigned long)min(tmp, (u64)(unsigned long)LONG_MAX);
}