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| author | Ingo Molnar <mingo@elte.hu> | 2007-08-09 09:16:51 (GMT) |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2007-08-09 09:16:51 (GMT) |
| commit | 194081ebfaa8c7d16133e08dd79254910c20c6ff (patch) | |
| tree | ba4d26c12614c93694fa67dd4003e243fe546e6c | |
| parent | 254753dc321ea2b753ca9bc58ac329557a20efac (diff) | |
| download | linux-194081ebfaa8c7d16133e08dd79254910c20c6ff.tar.xz | |
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>
| -rw-r--r-- | kernel/sched.c | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 5470ab0..b0afd8d 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -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); } |