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authorRik van Riel <riel@redhat.com>2015-11-05 15:56:22 -0500
committerIngo Molnar <mingo@kernel.org>2015-11-09 16:13:27 +0100
commit25b3e5a3344e1f700c1efec5b6f0199f04707fb1 (patch)
tree5f3b54f6f8f9a207fc717bda3902f47d83be91f0 /kernel
parent66ef3493d4bb387f5a83915e33dc893102fd1b43 (diff)
downloadop-kernel-dev-25b3e5a3344e1f700c1efec5b6f0199f04707fb1.zip
op-kernel-dev-25b3e5a3344e1f700c1efec5b6f0199f04707fb1.tar.gz
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@redhat.com> Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: mgorman@suse.de Link: http://lkml.kernel.org/r/1446756983-28173-2-git-send-email-riel@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/fair.c2
1 files changed, 1 insertions, 1 deletions
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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