linux-kernel - Re: [PATCH v2 0/7] Various tsc/clocksource fixes

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Date:   Tue, 01 May 2018 11:12:03 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, diego.viola@...il.com,
        len.brown@...el.com, rui.zhang@...el.com
Subject: Re: [PATCH v2 0/7] Various tsc/clocksource fixes

On Monday, April 30, 2018 12:00:08 PM CEST Peter Zijlstra wrote:
> These patches are the result of the regression Diego reported against commit:
> 
>   aa83c45762a2 ("x86/tsc: Introduce early tsc clocksource")
> 
> His Core2 triggers mark_tsc_unstable() while we're running with tsc-early,
> which then results in us failing to unregister the clocksource.
> 
> Furthermore, since mark_tsc_unstable() only looks at the regular tsc
> clocksource, we don't even mark tsc_early UNSTABLE or de-rate it, resulting in
> it actually staying a desirable clocksource.
> 
> Fixing that is a little more tricky; albeit far less critical after we
> guarantee to unregister tsc-early.
> 
> Please consider these for /urgent. I've used both Fixes and stable tags
> on a bunch of them because the above commit is already in v4.16 and
> would need stable help.
> 
> These patches have been tested on both a Core2 and an IVB. On IVB I've both
> changed intel_idle to always report the TSC unstable and mucked about with the
> TSC msr from userspace to tickle the watchdog paths.
> 
> ---
> Changes since v1
> 
>  - fix __clocksource_change_rating() locking
>  - removed work->kthread->watchdog hoops
>  - fixed up comment
> 
> 

I've had a deeper look at the patches and have not found anything of concern
in them, so for the whole series:

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>