[PATCH] x86/vmware: avoid TSC recalibration

[PATCH] x86/vmware: avoid TSC recalibration

[Alexey Makhalov]

When TSC frequency is known (retrieved from hypervisor), we should skip
TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ.

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
---
 arch/x86/kernel/cpu/vmware.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index c6ede3b3d302..83164110ccc5 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void)
 {
 	setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
 	setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
+	if (vmware_tsc_khz)
+		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 	if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
 		setup_force_cpu_cap(X86_FEATURE_VMCALL);
 	else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)
-- 
2.11.0

Re: [PATCH] x86/vmware: avoid TSC recalibration

[Vitaly Kuznetsov]

Alexey Makhalov <amakhalov@vmware.com> writes:

> When TSC frequency is known (retrieved from hypervisor), we should skip
> TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
>
> Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
> ---
>  arch/x86/kernel/cpu/vmware.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index c6ede3b3d302..83164110ccc5 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void)
>  {
>  	setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
>  	setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
> +	if (vmware_tsc_khz)
> +		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
>  	if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
>  		setup_force_cpu_cap(X86_FEATURE_VMCALL);
>  	else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)

The same trick is being used in Xen/Jailhouse/KVM code already and
Hyper-V overwrites x86_platform.calibrate_tsc/x86_platform.calibrate_cpu
hooks to basically achive the same goal. Should we maybe introduce a
flag in 'struct hypervisor_x86' or something like that to unify all
this?

Just a suggestion.

-- 
Vitaly

Re: [PATCH] x86/vmware: avoid TSC recalibration

[Alexey Makhalov]

Hi Vitaly,

I believe, it is responsibility of each guest code to set X86_FEATURE_TSC_KNOWN_FREQ cap.
Regarding VMware guest, there is a case where vmware_tsc_khz is zero (not provided by hypervisor)
and TSC frequency should be calculated.

Sorry for late response.

Regards,
—Alexey

> On Jan 5, 2021, at 5:06 AM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> 
> Alexey Makhalov <amakhalov@vmware.com> writes:
> 
>> When TSC frequency is known (retrieved from hypervisor), we should skip
>> TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ.
>> 
>> Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
>> ---
>> arch/x86/kernel/cpu/vmware.c | 2 ++
>> 1 file changed, 2 insertions(+)
>> 
>> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
>> index c6ede3b3d302..83164110ccc5 100644
>> --- a/arch/x86/kernel/cpu/vmware.c
>> +++ b/arch/x86/kernel/cpu/vmware.c
>> @@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void)
>> {
>> 	setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
>> 	setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
>> +	if (vmware_tsc_khz)
>> +		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
>> 	if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
>> 		setup_force_cpu_cap(X86_FEATURE_VMCALL);
>> 	else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)
> 
> The same trick is being used in Xen/Jailhouse/KVM code already and
> Hyper-V overwrites x86_platform.calibrate_tsc/x86_platform.calibrate_cpu
> hooks to basically achive the same goal. Should we maybe introduce a
> flag in 'struct hypervisor_x86' or something like that to unify all
> this?
> 
> Just a suggestion.
> 
> -- 
> Vitaly

[tip: x86/vmware] x86/vmware: Avoid TSC recalibration when frequency is known

[tip-bot2 for Alexey Makhalov]

The following commit has been merged into the x86/vmware branch of tip:

Commit-ID:     0b4a285e2c65c2c9449c6eccb87298e385213e7b
Gitweb:        https://git.kernel.org/tip/0b4a285e2c65c2c9449c6eccb87298e385213e7b
Author:        Alexey Makhalov <amakhalov@vmware.com>
AuthorDate:    Mon, 04 Jan 2021 16:47:52 -08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sun, 28 Mar 2021 21:11:43 +02:00

x86/vmware: Avoid TSC recalibration when frequency is known

When the TSC frequency is known because it is retrieved from the
hypervisor, skip TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ.

Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210105004752.131069-1-amakhalov@vmware.com

---
 arch/x86/kernel/cpu/vmware.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index c6ede3b..8316411 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void)
 {
 	setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
 	setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
+	if (vmware_tsc_khz)
+		setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 	if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
 		setup_force_cpu_cap(X86_FEATURE_VMCALL);
 	else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)