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[PATCH] sched/fair: refine maximum periods for decay_load

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In current code, decay_load() will consider to set load value to zero
after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.

Kernel can support maximum number of processes and threads to 2^29 and
set task with highest priority with nice=-20 (weight = 88761). So in
worst case, one CPU may have maximum load value is:

    max_load = 2^29 * 88761 < 2^46

In theory after pass 46 periods we can ensure load value will be decayed
to zero. So this patch is to change maximum periods from 64 to 48.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e342159..55cb134 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)
 
 	if (!n)
 		return val;
-	else if (unlikely(n > LOAD_AVG_PERIOD * 63))
+	else if (unlikely(n > LOAD_AVG_PERIOD * 47))
 		return 0;
 
 	/* after bounds checking we can collapse to 32-bit */
-- 
1.9.1

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[PATCH] sched/fair: refine maximum periods for decay_load Leo Yan <leo.yan@linaro.org> - 2016-08-05 08:40 +0200
  Re: [PATCH] sched/fair: refine maximum periods for decay_load Vincent Guittot <vincent.guittot@linaro.org> - 2016-08-05 10:00 +0200
    Re: [PATCH] sched/fair: refine maximum periods for decay_load Leo Yan <leo.yan@linaro.org> - 2016-08-05 10:20 +0200
      Re: [PATCH] sched/fair: refine maximum periods for decay_load Vincent Guittot <vincent.guittot@linaro.org> - 2016-08-05 10:40 +0200

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