[PATCH 2/2] clockevents: Prefer clockevents that don't suffer from FEAT_C3_STOP

Stephen Boyd sboyd at codeaurora.org
Thu Aug 22 13:06:41 EDT 2013

On some ARM systems there are two sets of per-cpu timers: the TWD
timers and the global timers. The TWD timers are rated at 350 and
the global timers are rated at 300 but the TWD timers suffer from
FEAT_C3_STOP while the arm global timers don't. The tick device
selection logic doesn't consider the FEAT_C3_STOP flag so we'll
always end up with the TWD as the tick device although we don't
want that.

Extend the preference logic to take the FEAT_C3_STOP flag into
account and always prefer tick devices that don't suffer from
FEAT_C3_STOP even if their rating is lower than tick devices that
do suffer from FEAT_C3_STOP. This will remove the need to do any
broadcasting on such ARM systems.

Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
 kernel/time/tick-common.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 64522ec..3ae437d 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -244,12 +244,22 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
 			return false;
+	if (!curdev)
+		return true;
+	/* Always prefer a tick device that doesn't suffer from FEAT_C3STOP */
+	if (!(newdev->features & CLOCK_EVT_FEAT_C3STOP) &&
+			(curdev->features & CLOCK_EVT_FEAT_C3STOP))
+		return true;
+	if ((newdev->features & CLOCK_EVT_FEAT_C3STOP) &&
+			!(curdev->features & CLOCK_EVT_FEAT_C3STOP))
+		return false;
 	 * Use the higher rated one, but prefer a CPU local device with a lower
 	 * rating than a non-CPU local device
-	return !curdev ||
-		newdev->rating > curdev->rating ||
+       return newdev->rating > curdev->rating ||
 	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
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