Commit 194081eb authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
parent 254753dc

kernel/sched.c

+11 −7
Original line number Diff line number Diff line
@@ -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);

}