diff mbox series

[focal:linux-azure,SRU,v2,4/4] clocksource/drivers/hyper-v: Set TSC clocksource as default w/ InvariantTSC

Message ID 20200812184246.14738-5-kelsey.skunberg@canonical.com
State New
Headers show
Series LP#:1875467: Enable invariant TSC | expand

Commit Message

Kelsey Skunberg Aug. 12, 2020, 6:42 p.m. UTC 
From: Andrea Parri <parri.andrea@gmail.com>

BugLink: https://bugs.launchpad.net/bugs/1875467

Change the Hyper-V clocksource ratings to 250, below the TSC clocksource
rating of 300.  In configurations where Hyper-V offers an InvariantTSC,
the TSC is not marked "unstable", so the TSC clocksource is available
and preferred.  With the higher rating, it will be the default.  On
older hardware and Hyper-V versions, the TSC is marked "unstable", so no
TSC clocksource is created and the selected Hyper-V clocksource will be
the default.

Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200109160650.16150-3-parri.andrea@gmail.com
(backported from commit 9e0333ae38eeb42249e10f95d209244a6e22ac9f)
[KelseyS: context changes to allow backporting]
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>
---
 drivers/clocksource/hyperv_timer.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index 3325ec9bc67e..038539ab019a 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -302,6 +302,14 @@  EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
  * the other that uses the TSC reference page feature as defined in the
  * TLFS.  The MSR version is for compatibility with old versions of
  * Hyper-V and 32-bit x86.  The TSC reference page version is preferred.
+ *
+ * The Hyper-V clocksource ratings of 250 are chosen to be below the
+ * TSC clocksource rating of 300.  In configurations where Hyper-V offers
+ * an InvariantTSC, the TSC is not marked "unstable", so the TSC clocksource
+ * is available and preferred.  With the higher rating, it will be the
+ * default.  On older hardware and Hyper-V versions, the TSC is marked
+ * "unstable", so no TSC clocksource is created and the selected Hyper-V
+ * clocksource will be the default.
  */
 
 struct clocksource *hyperv_cs;
@@ -356,7 +364,7 @@  static void resume_hv_clock_tsc(struct clocksource *arg)
 
 static struct clocksource hyperv_cs_tsc = {
 	.name	= "hyperv_clocksource_tsc_page",
-	.rating	= 400,
+	.rating	= 250,
 	.read	= read_hv_clock_tsc,
 	.mask	= CLOCKSOURCE_MASK(64),
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
@@ -384,7 +392,7 @@  static u64 read_hv_sched_clock_msr(void)
 
 static struct clocksource hyperv_cs_msr = {
 	.name	= "hyperv_clocksource_msr",
-	.rating	= 400,
+	.rating	= 250,
 	.read	= read_hv_clock_msr,
 	.mask	= CLOCKSOURCE_MASK(64),
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,