linux-kernel - Re: [PATCH v4 00/10] make L2's kvm-clock stable, get rid of pvclock_gtod

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Message-ID: <97db951d-326d-daa1-e619-4348b7eb4e70@redhat.com>
Date:   Wed, 2 Aug 2017 18:10:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Denis Plotnikov <dplotnikov@...tuozzo.com>, rkrcmar@...hat.com,
        kvm@...r.kernel.org, john.stultz@...aro.org, tglx@...utronix.de
Cc:     mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, rkagan@...tuozzo.com, den@...tuozzo.com
Subject: Re: [PATCH v4 00/10] make L2's kvm-clock stable, get rid of
 pvclock_gtod_copy in KVM

On 02/08/2017 16:38, Denis Plotnikov wrote:
> V4:
>   * removed "is stable" function with vague definition of stability
>     there is the only function which does time with cycle stamp getting
>   * some variables renamed
>   * some patches split into smaller once
>   * atomic64_t usage is replaced with atomic_t

Thanks.  This looks good from the KVM point of view.  Let's see what the
timekeeping guys think.

Paolo

> V3:
>   Changing the timekeeper interface for clocksource reading looks like
>   an overkill to achive the goal of getting cycles stamp for KVM.
>   Instead extend the timekeeping interface and add functions which provide
>   necessary data: read clocksource with cycles stamp, check whether the
>   clock source is stable.
> 
>   Use those functions and improve existing timekeeper functionality to
>   replace pvclock_gtod_copy scheme in masterclock data calculation.
> 
> V2:
>   The main goal is to make L2 kvm-clock be stable when it's running over L1
>   with stable kvm-clock.
> 
>   The patch series is for x86 architecture only. If the series is approved
>   I'll do changes for other architectures but I don't have an ability to
>   compile and check for every single on (help needed)
> 
>   The patch series do the following:
> 
>         * change timekeeper interface to get cycles stamp value from
>           the timekeeper
>         * get rid of pvclock copy in KVM by using the changed timekeeper
>           interface: get time and cycles right from the timekeeper
>         * make KVM recognize a stable kvm-clock as stable clocksource
>           and use the KVM masterclock in this case, which means making
>           L2 stable when running over stable L1 kvm-clock
> 
> Denis Plotnikov (10):
>   timekeeper: introduce extended clocksource reading callback
>   timekeeper: introduce boot field in system_time_snapshot
>   timekeeper: use the extended reading function on snapshot acquiring
>   tsc: implement the extended tsc reading function
>   KVM: x86: switch to masterclock update using timekeeper functionality
>   timekeeper: add clocksource change notifier
>   KVM: x86: remove not used pvclock_gtod_copy
>   pvclock: add parameters to store stamp data in pvclock reading
>     function
>   pvclock: add clocksource change notification on changing of tsc stable
>     bit
>   kvmclock: implement the extended reading function
> 
>  arch/x86/include/asm/kvm_host.h |   2 +-
>  arch/x86/include/asm/pvclock.h  |   3 +-
>  arch/x86/kernel/kvmclock.c      |  19 +++-
>  arch/x86/kernel/pvclock.c       |  37 +++++-
>  arch/x86/kernel/tsc.c           |  10 ++
>  arch/x86/kvm/trace.h            |  31 ++---
>  arch/x86/kvm/x86.c              | 242 ++++++++--------------------------------
>  arch/x86/xen/time.c             |   2 +-
>  include/linux/clocksource.h     |  11 +-
>  include/linux/cs_notifier.h     |  17 +++
>  include/linux/timekeeping.h     |   5 +
>  kernel/time/timekeeping.c       |  68 ++++++++++-
>  12 files changed, 219 insertions(+), 228 deletions(-)
>  create mode 100644 include/linux/cs_notifier.h
>