linux-kernel - Re: [PATCH v5 0/6] KVM: x86: get rid of pvclock_gtod

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Date:   Mon, 11 Sep 2017 12:24:10 +0300
From:   Denis Plotnikov <dplotnikov@...tuozzo.com>
To:     pbonzini@...hat.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 v5 0/6] KVM: x86: get rid of pvclock_gtod_copy

ping!

On 30.08.2017 18:23, Denis Plotnikov wrote:
> V5:
>    It was decided to split the series
>    "make L2's kvm-clock stable, get rid of pvclock_gtod_copy in KVM"
>    into two parts to make the changes finer grained:
>      1. get rid of pvclock_gtod_copy in KVM
>      2. make L2's kvm-clock stable
>    This V5 series implements the 1st part. This part gets rid
>    of pvclock_gtod_copy by switching to use the timekeeper functionality
>    being extended. This new scheme doesn't add any new notifiers and keeps
>    using the existing one (see patch 6 description) which had been used by
>    the pvclock_gtod_copy to keep track timekeeper data changes.
> 
>    The 2nd part is being discussed and is going to be sent later on.
> 
> 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
>   
> 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 (6):
>    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
>    KVM: x86: remove not used pvclock_gtod_copy
> 
>   arch/x86/include/asm/kvm_host.h |   2 +-
>   arch/x86/kernel/tsc.c           |  10 ++
>   arch/x86/kvm/trace.h            |  31 ++---
>   arch/x86/kvm/x86.c              | 245 +++++++++-------------------------------
>   include/linux/clocksource.h     |  11 +-
>   include/linux/timekeeping.h     |   5 +
>   kernel/time/timekeeping.c       |  17 ++-
>   7 files changed, 104 insertions(+), 217 deletions(-)
> 

-- 
Best,
Denis