Commit-ID: 25b3e5a3344e1f700c1efec5b6f0199f04707fb1
Gitweb: http://git.kernel.org/tip/25b3e5a3344e1f700c1efec5b6f0199f04707fb1
Author: Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Thu, 5 Nov 2015 15:56:22 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 9 Nov 2015 16:13:27 +0100
sched/numa: Fix math underflow in task_tick_numa()
The NUMA balancing code implements delays in scanning by
advancing curr->node_stamp beyond curr->se.sum_exec_runtime.
With unsigned math, that creates an underflow, which results
in task_numa_work being queued all the time, even when we
don't want to.
Avoiding the math underflow makes it possible to reduce CPU
overhead in the NUMA balancing code.
Reported-and-tested-by: Jan Stancek <jstancek@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: mgorman@xxxxxxx
Link: http://lkml.kernel.org/r/1446756983-28173-2-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 824aa9f..f04fda8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2302,7 +2302,7 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr)
now = curr->se.sum_exec_runtime;
period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;
- if (now - curr->node_stamp > period) {
+ if (now > curr->node_stamp + period) {
if (!curr->node_stamp)
curr->numa_scan_period = task_scan_min(curr);
curr->node_stamp += period;
--
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