2021-01-05 01:08:37

by Alexey Makhalov

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

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 <[email protected]>
---
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

2021-01-05 20:40:58

by Vitaly Kuznetsov

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

Alexey Makhalov <[email protected]> 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 <[email protected]>
> ---
> 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

2021-03-15 22:42:07

by Alexey Makhalov

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

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 <[email protected]> wrote:
>
> Alexey Makhalov <[email protected]> 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 <[email protected]>
>> ---
>> 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

2021-03-28 19:19:12

by tip-bot2 for Jacob Pan

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

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 <[email protected]>
AuthorDate: Mon, 04 Jan 2021 16:47:52 -08:00
Committer: Thomas Gleixner <[email protected]>
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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

---
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)