Commit 25b3e5a3 authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
Browse files

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: default avatarJan Stancek <jstancek@redhat.com>
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 66ef3493
......@@ -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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