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[PATCH] sched: relax pinned balancing 

The maximum rebalance interval allowed by the multiprocessor balancing
backoff is often not large enough to handle corner cases where there are
lots of tasks pinned on a CPU.  Suresh reported:

	I see system livelock's if for example I have 7000 processes
	pinned onto one cpu (this is on the fastest 8-way system I
	have access to).

After this patch, the machine is reported to go well above this number.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Nick Piggin 2005-06-25 14:57:30 -07:00 committed by Linus Torvalds
parent 476d139c21
commit 77391d7168
1 changed files with 9 additions and 2 deletions
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11
kernel/sched.c
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@ -2030,6 +2030,12 @@ static runqueue_t *find_busiest_queue(struct sched_group *group)
return busiest;
}
/*
* Max backoff if we encounter pinned tasks. Pretty arbitrary value, but
* so long as it is large enough.
*/
#define MAX_PINNED_INTERVAL 512
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
@ -2042,7 +2048,7 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
struct sched_group *group;
runqueue_t *busiest;
unsigned long imbalance;
int nr_moved, all_pinned;
int nr_moved, all_pinned = 0;
int active_balance = 0;
spin_lock(&this_rq->lock);
@ -2133,7 +2139,8 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
sd->nr_balance_failed = 0;
/* tune up the balancing interval */
if (sd->balance_interval < sd->max_interval)
if ((all_pinned && sd->balance_interval < MAX_PINNED_INTERVAL) ||
(sd->balance_interval < sd->max_interval))
sd->balance_interval *= 2;
return 0;