From: Chenyi Qiang <chenyi.qiang@intel.com>
To: David Woodhouse <dwmw2@infradead.org>, <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>, Paul Durrant <paul@xen.org>,
Shuah Khan <shuah@kernel.org>, <linux-doc@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>,
"Oliver Upton" <oliver.upton@linux.dev>,
Marcelo Tosatti <mtosatti@redhat.com>, <jalliste@amazon.co.uk>,
<sveith@amazon.de>, <zide.chen@intel.com>,
"Dongli Zhang" <dongli.zhang@oracle.com>
Subject: Re: [PATCH v2 13/15] KVM: x86: Kill cur_tsc_{nsec,offset,write} fields
Date: Fri, 10 May 2024 17:03:28 +0800 [thread overview]
Message-ID: <0867c527-6fe5-4f54-adcc-0344e9416f9b@intel.com> (raw)
In-Reply-To: <20240427111929.9600-14-dwmw2@infradead.org>
On 4/27/2024 7:05 PM, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> These pointlessly duplicate of the last_tsc_{nsec,offset,write} values.
>
> The only place they were used was where the TSC is stable and a new vCPU
> is being synchronized to the previous setting, in which case the 'last_'
> value is definitely identical.
>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
> arch/x86/include/asm/kvm_host.h | 3 ---
> arch/x86/kvm/x86.c | 9 ++-------
> 2 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index b01c1d000fff..7d06f389a607 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1354,9 +1354,6 @@ struct kvm_arch {
> u32 last_tsc_khz;
> u64 last_tsc_offset;
> u64 last_tsc_scaling_ratio;
> - u64 cur_tsc_nsec;
> - u64 cur_tsc_write;
> - u64 cur_tsc_offset;
> u64 cur_tsc_generation;
> int nr_vcpus_matched_tsc;
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6ec43f39bdb0..92e81bfca25a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2737,9 +2737,6 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
> * These values are tracked in kvm->arch.cur_xxx variables.
> */
> kvm->arch.cur_tsc_generation++;
> - kvm->arch.cur_tsc_nsec = ns;
> - kvm->arch.cur_tsc_write = tsc;
> - kvm->arch.cur_tsc_offset = offset;
> kvm->arch.nr_vcpus_matched_tsc = 0;
> } else if (vcpu->arch.this_tsc_generation != kvm->arch.cur_tsc_generation) {
> kvm->arch.nr_vcpus_matched_tsc++;
> @@ -2747,8 +2744,6 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
>
> /* Keep track of which generation this VCPU has synchronized to */
> vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
> - vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
> - vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
Do we need to track vcpu->arch.this_tsc_nsec/this_tsc_write? At least
they are still used in compute_guest_tsc() to calculate the guest tsc.
>
> kvm_track_tsc_matching(vcpu);
> }
> @@ -2825,8 +2820,8 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value)
> data = kvm->arch.last_tsc_write;
>
> if (!kvm_check_tsc_unstable()) {
> - offset = kvm->arch.cur_tsc_offset;
> - ns = kvm->arch.cur_tsc_nsec;
> + offset = kvm->arch.last_tsc_offset;
> + ns = kvm->arch.last_tsc_nsec;
> } else {
> /*
> * ... unless the TSC is unstable and has to be
next prev parent reply other threads:[~2024-05-10 9:03 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-27 11:04 [RFC PATCH v2] Cleaning up the KVM clock mess David Woodhouse
2024-04-27 11:04 ` [PATCH v2 01/15] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init() David Woodhouse
2024-05-04 7:42 ` Marcelo Tosatti
2024-05-07 19:08 ` David Woodhouse
2024-04-27 11:04 ` [PATCH v2 02/15] KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force David Woodhouse
2024-04-27 11:05 ` [PATCH v2 03/15] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration David Woodhouse
2024-04-27 11:05 ` [PATCH v2 04/15] KVM: selftests: Add KVM/PV clock selftest to prove timer correction David Woodhouse
2024-04-27 11:05 ` [PATCH v2 05/15] KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC David Woodhouse
2024-04-27 11:05 ` [PATCH v2 06/15] KVM: x86: Add KVM_VCPU_TSC_SCALE and fix the documentation on TSC migration David Woodhouse
2024-04-27 11:05 ` [PATCH v2 07/15] KVM: x86: Avoid NTP frequency skew for KVM clock on 32-bit host David Woodhouse
2024-04-27 11:05 ` [PATCH v2 08/15] KVM: x86: Fix KVM clock precision in __get_kvmclock() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 09/15] KVM: x86: Fix software TSC upscaling in kvm_update_guest_time() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 10/15] KVM: x86: Simplify and comment kvm_get_time_scale() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 11/15] KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc_offset() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 12/15] KVM: x86: Improve synchronization in kvm_synchronize_tsc() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 13/15] KVM: x86: Kill cur_tsc_{nsec,offset,write} fields David Woodhouse
2024-05-10 9:03 ` Chenyi Qiang [this message]
2024-05-14 13:17 ` David Woodhouse
2024-04-27 11:05 ` [PATCH v2 14/15] KVM: x86: Allow KVM master clock mode when TSCs are offset from each other David Woodhouse
2024-04-27 11:05 ` [PATCH v2 15/15] KVM: x86: Factor out kvm_use_master_clock() David Woodhouse
2024-05-01 17:55 ` Chen, Zide
2024-05-01 20:45 ` David Woodhouse
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