* [PATCH] clocksource: Defer override invalidation unless clock is unstable
@ 2016-07-13 15:15 Kyle Walker
0 siblings, 0 replies; only message in thread
From: Kyle Walker @ 2016-07-13 15:15 UTC (permalink / raw)
To: john.stultz, tglx; +Cc: linux-kernel, Kyle Walker
The clock_select() operation will attempt to use the clocksource override
to apply the desired clocksource when the "clocksource=" boot parameter is
supplied. However, in the event that "clocksource=tsc" is used on a system
where there is a more desireable clocksource available, the boot parameter
fails. This is due to the TSC clocksource being installed unvalidated, but
the override being invalidated during the initial run through
clocksource_done_booting().
To address this condition, the override_name is only invalidated for
unstable clocksources. Otherwise, the override is left intact until after
the watchdog has validated the clocksource as stable/unstable.
Signed-off-by: Kyle Walker <kwalker@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
---
kernel/time/clocksource.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 56ece14..4c1bb2a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -600,9 +600,18 @@ static void __clocksource_select(bool skipcur)
*/
if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
/* Override clocksource cannot be used. */
- pr_warn("Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
- cs->name);
- override_name[0] = 0;
+ if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+ pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
+ cs->name);
+ override_name[0] = 0;
+ } else {
+ /*
+ * The override cannot be currently verified.
+ * Deferring to let the watchdog check.
+ */
+ pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
+ cs->name);
+ }
} else
/* Override clocksource can be used. */
best = cs;
--
2.5.5
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