[patch 4/4] x86: Adjust HPET MSI timer rating to work with tick_check_fallback_timer

[Venkatesh Pallipadi]

Before this change we had
Normal lapic_clockevent rating 100
hpet MSI (percpu) clockevent rating 110
Always Running lapic_clockevent rating 150

As a result, on systems that support HPET MSI, percpu clockevents got
priority over LAPIC timer. That was ok when systems supported deep
C-state. But, that was sub-optimal on systems that did not support deep
C-states as HPETs are slower than LAPIC.

There was also a functional issue with usage of HPET MSI on some
platforms, which do not support deep C-state as reported here.
http://lkml.indiana.edu/hypermail/linux/kernel/0912.2/01118.html

After the change,
hpet MSI (percpu) clockevent rating 95
Normal lapic_clockevent rating 100
Always Running lapic_clockevent rating 150

And we reduce the rating of non-Always_Running LAPIC timer (to 90),
when we see that deep C-states are supported and switch to hpet MSI.

This change makes the timer usage optimal in terms of performance and
also eliminates the functionality issue mentioned above.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
---
 arch/x86/kernel/hpet.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index dd9370b..ccb3752 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -555,7 +555,11 @@ static void init_one_hpet_msi_clockevent(struct hpet_dev *hdev, int cpu)
 	hpet_setup_irq(hdev);
 	evt->irq = hdev->irq;
 
-	evt->rating = 110;
+	/*
+	 * Rating should be within 10 less than lapic timer for
+	 * timer switch to happen when deep C-states are supported.
+	 */
+	evt->rating = 95;
 	evt->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_NO_BROADCAST;
 	if (hdev->flags & HPET_DEV_PERI_CAP)
 		evt->features |= CLOCK_EVT_FEAT_PERIODIC;
-- 
1.6.0.6

-- 

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