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>
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 @@
#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 @@
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);
}