linux-kernel - RE: [PATCH 2/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function

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Message-ID: <DM5PR21MB01371937B0E72671C4B7C990D7D30@DM5PR21MB0137.namprd21.prod.outlook.com>
Date:   Mon, 12 Aug 2019 18:41:38 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     "lantianyu1986@...il.com" <lantianyu1986@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "ashal@...nel.org" <ashal@...nel.org>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [PATCH 2/2] clocksource/Hyper-V:  Add Hyper-V specific sched
 clock function

From: Tianyu Lan <Tianyu.Lan@...rosoft.com>  Sent: Monday, July 29, 2019 12:53 AM
> 
> Hyper-V guests use the default native_sched_clock() in pv_ops.time.sched_clock
> on x86.  But native_sched_clock() directly uses the raw TSC value, which
> can be discontinuous in a Hyper-V VM. Add the generic hv_setup_sched_clock()
> to set the sched clock function appropriately. On x86, this sets pv_ops.time.
> sched_clock to read the Hyper-V reference TSC value that is scaled and adjusted
> to be continuous.
> 
> Also move the Hyper-V reference TSC initialization much earlier in the boot
> process so no discontinuity is observed when pv_ops.time.sched_clock
> calculates its offset.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
>  arch/x86/hyperv/hv_init.c          |  2 --
>  arch/x86/kernel/cpu/mshyperv.c     |  8 ++++++++
>  drivers/clocksource/hyperv_timer.c | 22 ++++++++++++----------
>  include/asm-generic/mshyperv.h     |  1 +
>  4 files changed, 21 insertions(+), 12 deletions(-)
> 

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>