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Re: [PATCH v3 09/41] clocksource: hyper-v: Don't save/restore TSC offset when using HV sched_clock
- To: Sean Christopherson <seanjc@xxxxxxxxxx>, Kiryl Shutsemau <kas@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Wei Liu <wei.liu@xxxxxxxxxx>, Dexuan Cui <decui@xxxxxxxxxxxxx>, Long Li <longli@xxxxxxxxxxxxx>, Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>, Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>, Jan Kiszka <jan.kiszka@xxxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxx>, John Stultz <jstultz@xxxxxxxxxx>
- From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
- Date: Wed, 20 May 2026 22:30:41 +0100
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- Cc: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stephen Boyd <sboyd@xxxxxxxxxx>, x86@xxxxxxxxxx, linux-coco@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Michael Kelley <mhklinux@xxxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Nikunj A Dadhania <nikunj@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- Delivery-date: Wed, 20 May 2026 21:30:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote:
> Now that Hyper-V overrides the sched_clock save/restore hooks if and only
> sched_clock itself is set to the Hyper-V reference counter, drop the
> invocation of the "old" save/restore callbacks. When the registration of
> the PV sched_clock was done separately from overriding the save/restore
> hooks, it was possible for Hyper-V to clobber the TSC save/restore
> callbacks without actually switching to the Hyper-V refcounter.
>
> Enabling a PV sched_clock is a one-way street, i.e. the kernel will never
> revert to using TSC for sched_clock, and so there is no need to invoke the
> TSC save/restore hooks (and if there was, it belongs in common PV code).
>
> Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
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