From: Sean Christopherson <seanjc@google.com>
To: Simon Veith <sveith@amazon.de>
Cc: dwmw2@infradead.org, dff@amazon.com, jmattson@google.com,
joro@8bytes.org, kvm@vger.kernel.org, oupton@google.com,
pbonzini@redhat.com, tglx@linutronix.de, vkuznets@redhat.com,
wanpengli@tencent.com
Subject: Re: [PATCH v2] KVM: x86: add KVM_VCPU_TSC_VALUE attribute
Date: Wed, 15 Mar 2023 12:57:22 -0700 [thread overview]
Message-ID: <ZBIjImc+xEMhJkQM@google.com> (raw)
In-Reply-To: <20230202165950.483430-1-sveith@amazon.de>
Please don't send vN+1 In-Reply-To vN, the threading messes up lore and other
tooling, and becomes really problematic for humans when N gets large.
On Thu, Feb 02, 2023, Simon Veith wrote:
> In the case of live migration, using the KVM_VCPU_TSC_OFFSET approach to
> preserve the TSC value and apply a known offset would require
> duplicating the TSC scaling computations in userspace to account for
> frequency differences between source and destination TSCs.
>
> Hence, if userspace wants to set the TSC to some known value without
> having to deal with TSC scaling, and while also being resilient against
> scheduling delays, neither KVM_SET_MSRS nor KVM_VCPU_TSC_VALUE are
> suitable options.
Requiring userspace to handle certain aspects of TSC scaling doesn't seem
particularly onerous, at least not relative to all the other time insanity. In
other words, why should KVM take on more complexity and a mostly-redundant uAPI?
next prev parent reply other threads:[~2023-03-15 19:57 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-22 19:18 [PATCH] Documentation: KVM: Describe guest TSC scaling in migration algorithm Franke, Daniel
2022-03-22 21:53 ` Oliver Upton
2022-03-23 12:35 ` David Woodhouse
2022-03-23 16:21 ` Oliver Upton
2022-03-25 9:03 ` David Woodhouse
2022-03-25 17:47 ` Oliver Upton
2022-03-29 14:19 ` Thomas Gleixner
2022-03-29 16:02 ` Oliver Upton
2022-03-29 19:34 ` Thomas Gleixner
2022-06-30 11:58 ` David Woodhouse
2022-07-05 14:43 ` David Woodhouse
2022-07-07 16:43 ` [PATCH 1/2] KVM: x86: add KVM clock time reference arg to kvm_write_tsc() Simon Veith
2022-07-07 16:43 ` [PATCH 2/2] KVM: x86: add KVM_VCPU_TSC_VALUE attribute Simon Veith
2022-07-29 21:21 ` Sean Christopherson
2022-07-29 21:14 ` [PATCH 1/2] KVM: x86: add KVM clock time reference arg to kvm_write_tsc() Sean Christopherson
2023-02-02 16:35 ` David Woodhouse
2023-02-02 16:59 ` [PATCH v2] KVM: x86: add KVM_VCPU_TSC_VALUE attribute Simon Veith
2023-03-15 19:57 ` Sean Christopherson [this message]
2023-03-23 23:26 ` David Woodhouse
2023-03-24 11:22 ` Paolo Bonzini
2023-03-24 13:08 ` David Woodhouse
2023-09-13 14:08 ` David Woodhouse
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