linux-kernel - Re: [PATCH v5 05/16] clocksource/hyperv: use MSR-based access if running as root

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Date:   Tue, 26 Jan 2021 15:19:58 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v5 05/16] clocksource/hyperv: use MSR-based access if
 running as root

On Wed, Jan 20, 2021 at 11:13:28AM -0500, Pavel Tatashin wrote:
> On Wed, Jan 20, 2021 at 7:01 AM Wei Liu <wei.liu@...nel.org> wrote:
> >
> > When Linux runs as the root partition, the setup required for TSC page
> > is different.
> 
> Why would we need a TSC page as a clock source for root partition at
> all? I think the above can be removed.
> 

The TSC page is considered superior to MSR-based clock. In the future we
may want to switch back to that TSC page instead.

I think it provides more context than without.

Wei.

>  Luckily Linux also has access to the MSR based
> > clocksource. We can just disable the TSC page clocksource if Linux is
> > the root partition.
> >