[PATCH 2/4] arch, x86, tsc deadline clockevent dev: reduce TSC_DIVISOR to 2

[Nicolai Stange]

In order to avoid overflowing an u32, the TSC deadline clockevent device's
frequency is divided by TSC_DIVISOR at registration.

The TSC_DIVISOR is currently defined as equaling 32 which allows for a
TSC frequency as high as 2^32 / 10^9ns * 32 = 137 GHz.

OTOH, larger values of TSC_DIVISOR introduce bigger roundoff errors into
the device's frequency.

A value of 2 for TSC_DIVISOR allows for a TSC frequency of
2^32 / 10^9ns * 2 = 8.5 GHz which is still way larger than anything to
expect in the next years.

Reduce the TSC deadline clockevent device's TSC_DIVISOR from 32 down to 2.

Signed-off-by: Nicolai Stange 
---
 arch/x86/kernel/apic/apic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index dce654c..1d22c72 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -311,7 +311,7 @@ int lapic_get_maxlvt(void)
 
 /* Clock divisor */
 #define APIC_DIVISOR 16
-#define TSC_DIVISOR  32
+#define TSC_DIVISOR  2
 
 /*
  * This function sets up the local APIC timer, with a timeout of
-- 
2.9.0

[PATCH 2/4] arch, x86, tsc deadline clockevent dev: reduce TSC_DIVISOR to 2

[Nicolai Stange]

In order to avoid overflowing an u32, the TSC deadline clockevent device's
frequency is divided by TSC_DIVISOR at registration.

The TSC_DIVISOR is currently defined as equaling 32 which allows for a
TSC frequency as high as 2^32 / 10^9ns * 32 = 137 GHz.

OTOH, larger values of TSC_DIVISOR introduce bigger roundoff errors into
the device's frequency.

A value of 2 for TSC_DIVISOR allows for a TSC frequency of
2^32 / 10^9ns * 2 = 8.5 GHz which is still way larger than anything to
expect in the next years.

Reduce the TSC deadline clockevent device's TSC_DIVISOR from 32 down to 2.

Signed-off-by: Nicolai Stange 
---
 arch/x86/kernel/apic/apic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index dce654c..1d22c72 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -311,7 +311,7 @@ int lapic_get_maxlvt(void)
 
 /* Clock divisor */
 #define APIC_DIVISOR 16
-#define TSC_DIVISOR  32
+#define TSC_DIVISOR  2
 
 /*
  * This function sets up the local APIC timer, with a timeout of
-- 
2.9.0