Commit 8e1bc301 authored by Tommaso Cucinotta's avatar Tommaso Cucinotta Committed by Ingo Molnar
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sched/deadline: Make CPU heap faster avoiding real swaps on heapify 



This change goes from heapify() ops done by swapping with parent/child
so that the item to fix moves along, to heapify() ops done by just
pulling the parent/child chain by 1 pos, then storing the item to fix
just at the end. On a non-trivial heapify(), this performs roughly half
stores wrt swaps.

This has been measured to achieve up to 10% of speed-up for cpudl_set()
calls, with a randomly generated workload of 1K,10K,100K random heap
insertions and deletions (75% cpudl_set() calls with is_valid=1 and
25% with is_valid=0), and randomly generated cpu IDs, with up to 256
CPUs, as measured on an Intel Core2 Duo.

Signed-off-by: default avatarTommaso Cucinotta <tommaso.cucinotta@sssup.it>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarLuca Abeni <luca.abeni@unitn.it>
Reviewed-by: default avatarJuri Lelli <juri.lelli@arm.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-dl@retis.sssup.it
Link: http://lkml.kernel.org/r/1471184828-12644-3-git-send-email-tommaso.cucinotta@sssup.it


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 126b3b68

kernel/sched/cpudeadline.c

+45 −21
Original line number Diff line number Diff line
@@ -31,48 +31,72 @@ static inline int right_child(int i) 
	return (i << 1) + 2;

}



static void cpudl_exchange(struct cpudl *cp, int a, int b)

{

	int cpu_a = cp->elements[a].cpu, cpu_b = cp->elements[b].cpu;



	swap(cp->elements[a].cpu, cp->elements[b].cpu);

	swap(cp->elements[a].dl , cp->elements[b].dl );



	swap(cp->elements[cpu_a].idx, cp->elements[cpu_b].idx);

}



static void cpudl_heapify_down(struct cpudl *cp, int idx)

{

	int l, r, largest;



	int orig_cpu = cp->elements[idx].cpu;

	u64 orig_dl = cp->elements[idx].dl;



	if (left_child(idx) >= cp->size)

		return;



	/* adapted from lib/prio_heap.c */

	while(1) {

		u64 largest_dl;

		l = left_child(idx);

		r = right_child(idx);

		largest = idx;

		largest_dl = orig_dl;



		if ((l < cp->size) && dl_time_before(cp->elements[idx].dl,

							cp->elements[l].dl))

		if ((l < cp->size) && dl_time_before(orig_dl,

						cp->elements[l].dl)) {

			largest = l;

		if ((r < cp->size) && dl_time_before(cp->elements[largest].dl,

			largest_dl = cp->elements[l].dl;

		}

		if ((r < cp->size) && dl_time_before(largest_dl,

						cp->elements[r].dl))

			largest = r;



		if (largest == idx)

			break;



		/* Push idx down the heap one level and bump one up */

		cpudl_exchange(cp, largest, idx);

		/* pull largest child onto idx */

		cp->elements[idx].cpu = cp->elements[largest].cpu;

		cp->elements[idx].dl = cp->elements[largest].dl;

		cp->elements[cp->elements[idx].cpu].idx = idx;

		idx = largest;

	}

	/* actual push down of saved original values orig_* */

	cp->elements[idx].cpu = orig_cpu;

	cp->elements[idx].dl = orig_dl;

	cp->elements[cp->elements[idx].cpu].idx = idx;

}



static void cpudl_heapify_up(struct cpudl *cp, int idx)

{

	while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,

			cp->elements[idx].dl)) {

		cpudl_exchange(cp, idx, parent(idx));

		idx = parent(idx);

	}

	int p;



	int orig_cpu = cp->elements[idx].cpu;

	u64 orig_dl = cp->elements[idx].dl;



	if (idx == 0)

		return;



	do {

		p = parent(idx);

		if (dl_time_before(orig_dl, cp->elements[p].dl))

			break;

		/* pull parent onto idx */

		cp->elements[idx].cpu = cp->elements[p].cpu;

		cp->elements[idx].dl = cp->elements[p].dl;

		cp->elements[cp->elements[idx].cpu].idx = idx;

		idx = p;

	} while (idx != 0);

	/* actual push up of saved original values orig_* */

	cp->elements[idx].cpu = orig_cpu;

	cp->elements[idx].dl = orig_dl;

	cp->elements[cp->elements[idx].cpu].idx = idx;

}



static void cpudl_heapify(struct cpudl *cp, int idx)

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