[PATCH] x86/vmware: Skip lapic calibration on VMware.

[PATCH] x86/vmware: Skip lapic calibration on VMware.

[Renat Valiullin]

In virtualized environment the APIC timer calibration could go wrong
when the host is overcommitted or the guest is running nested,
this would result in the APIC timers operating at an incorrect frequency.
Since VMware supports a mechanism to retrieve the local APIC frequency
we can ask the hypervisor for it and skip this APIC calibration loop.

Signed-off-by: Renat Valiullin <rvaliullin@vmware.com>
Acked-by: Alok N Kataria <akataria@vmware.com>
---
 arch/x86/kernel/cpu/vmware.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index 1ff0598..8116057 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -27,6 +27,7 @@
 #include <asm/div64.h>
 #include <asm/x86_init.h>
 #include <asm/hypervisor.h>
+#include <asm/apic.h>
 
 #define CPUID_VMWARE_INFO_LEAF	0x40000000
 #define VMWARE_HYPERVISOR_MAGIC	0x564D5868
@@ -82,10 +83,17 @@ static void __init vmware_platform_setup(void)
 
 	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
 
-	if (ebx != UINT_MAX)
+	if (ebx != UINT_MAX) {
 		x86_platform.calibrate_tsc = vmware_get_tsc_khz;
-	else
+#ifdef CONFIG_X86_LOCAL_APIC
+		/* Skip lapic calibration since we know the bus frequency. */
+		lapic_timer_frequency = ecx / HZ;
+		pr_info("Host bus clock speed read from hypervisor : %u Hz\n",
+			ecx);
+#endif
+	} else {
 		pr_warn("Failed to get TSC freq from the hypervisor\n");
+	}
 }
 
 /*
-- 
2.7.4

Re: [PATCH] x86/vmware: Skip lapic calibration on VMware.

[Thomas Gleixner]

[-- Attachment #1: Type: text/plain, Size: 1469 bytes --]

On Thu, 29 Sep 2016, Renat Valiullin wrote:
> In virtualized environment the APIC timer calibration could go wrong
> when the host is overcommitted or the guest is running nested,
> this would result in the APIC timers operating at an incorrect frequency.
> Since VMware supports a mechanism to retrieve the local APIC frequency
> we can ask the hypervisor for it and skip this APIC calibration loop.
> 
> Signed-off-by: Renat Valiullin <rvaliullin@vmware.com>
> Acked-by: Alok N Kataria <akataria@vmware.com>
> ---
>  arch/x86/kernel/cpu/vmware.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)

Please fix your mail client so it does not mangle the patch into DOS
format. Aside of that it's white space mangled, i.e. the tabs are converted
to spaces.
 
Please send your patch to yourself, export it to a mbox and apply it with
git am.

> -       if (ebx != UINT_MAX)
> +       if (ebx != UINT_MAX) {
>                 x86_platform.calibrate_tsc = vmware_get_tsc_khz;
> -       else
> +#ifdef CONFIG_X86_LOCAL_APIC
> +               /* Skip lapic calibration since we know the bus frequency. */
> +               lapic_timer_frequency = ecx / HZ;
> +               pr_info("Host bus clock speed read from hypervisor : %u Hz\n",
> +                       ecx);
> +#endif
> +       } else
>                 pr_warn("Failed to get TSC freq from the hypervisor\n");

Please add braces around this as well. See Documentation/Codingstyle

Thanks,

	tglx

[-- Attachment #2: Type: text/plain, Size: 183 bytes --]

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[PATCH] x86/vmware: Skip lapic calibration on VMware.

[Renat Valiullin]

In virtualized environment the APIC timer calibration could go wrong
when the host is overcommitted or the guest is running nested,
this would result in the APIC timers operating at an incorrect frequency.
Since VMware supports a mechanism to retrieve the local APIC frequency
we can ask the hypervisor for it and skip this APIC calibration loop.

Signed-off-by: Renat Valiullin <rvaliullin@vmware.com>
Acked-by: Alok N Kataria <akataria@vmware.com>
---
 arch/x86/kernel/cpu/vmware.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index 1ff0598..6316240 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -27,6 +27,7 @@
 #include <asm/div64.h>
 #include <asm/x86_init.h>
 #include <asm/hypervisor.h>
+#include <asm/apic.h>

 #define CPUID_VMWARE_INFO_LEAF 0x40000000
 #define VMWARE_HYPERVISOR_MAGIC        0x564D5868
@@ -82,9 +83,15 @@ static void __init vmware_platform_setup(void)

        VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);

-       if (ebx != UINT_MAX)
+       if (ebx != UINT_MAX) {
                x86_platform.calibrate_tsc = vmware_get_tsc_khz;
-       else
+#ifdef CONFIG_X86_LOCAL_APIC
+               /* Skip lapic calibration since we know the bus frequency. */
+               lapic_timer_frequency = ecx / HZ;
+               pr_info("Host bus clock speed read from hypervisor : %u Hz\n",
+                       ecx);
+#endif
+       } else
                pr_warn("Failed to get TSC freq from the hypervisor\n");
 }

-- 
2.7.4


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