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sched/deadline: Make CPU heap faster avoiding real swaps on heapify

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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: Tommaso Cucinotta <tommaso.cucinotta@sssup.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Luca Abeni <luca.abeni@unitn.it>
Reviewed-by: Juri 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Tommaso Cucinotta 2016-08-14 16:27:07 +02:00 committed by Ingo Molnar
parent 126b3b6842
commit 8e1bc301aa
1 changed files with 45 additions and 21 deletions
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66
kernel/sched/cpudeadline.c
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@ -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,
cp->elements[r].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)