Commit 0514073f authored Jun 26, 2018 by Pavankumar Kondeti Committed by Lingutla Chandrasekhar Jul 20, 2018

sched: walt: Add BUG_ON() when wallclock goes backwards

This reverts 'commit b5e1207658f0 ("ANDROID: arch_timer: add error
handling when the MPM global timer is cleared")'

The above mentioned commit removed a BUG_ON() which gets hit, when
the wallclock goes backwards compared to the rq->window_start. This
condition is fatal for WALT accounting. The update_task_ravg() strictly
expects the wallclock - rq->window_start to be positive and when it
becomes negative, the accounting issues would show up at later point
of time which makes debugging difficult.

This BUG_ON() is a false positive only when the MPM global timer is
cleared and CPUs are running for a short time during force reset. It
is very easy to identify this condition than debugging the scheduler
accounting and time going backwards issues. So add the BUG_ON() back.

Change-Id: Ib52862abb9448dc6db70bb7db958d11545db095f
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

parent 907327c1

kernel/sched/walt.c

+1 −9

Original line number	Diff line number	Diff line
		@@ -272,15 +272,7 @@ update_window_start(struct rq *rq, u64 wallclock, int event)
		u64 old_window_start = rq->window_start;

		delta = wallclock - rq->window_start;
		/*
		* If the MPM global timer is cleared, set delta as 0 to
		* avoid kernel BUG happening
		*/
		if (delta < 0) {
		delta = 0;
		WARN_ONCE(1, "WALT wallclock appears to have gone backwards or reset\n");
		}

		BUG_ON(delta < 0);
		if (delta < sched_ravg_window)
		return old_window_start;