netdev - Re: [RFC PATCH V2 11/11] x86: tsc: avoid system instability in hibernation

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Date:   Mon, 13 Jan 2020 13:42:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Singh, Balbir" <sblbir@...zon.com>
Cc:     "Valentin, Eduardo" <eduval@...zon.com>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Agarwal, Anchal" <anchalag@...zon.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "Woodhouse@...-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com" 
        <Woodhouse@...-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com>,
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Subject: Re: [RFC PATCH V2 11/11] x86: tsc: avoid system instability in
 hibernation

On Mon, Jan 13, 2020 at 11:43:18AM +0000, Singh, Balbir wrote:
> For your original comment, just wanted to clarify the following:
> 
> 1. After hibernation, the machine can be resumed on a different but compatible
> host (these are VM images hibernated)
> 2. This means the clock between host1 and host2 can/will be different
> 
> In your comments are you making the assumption that the host(s) is/are the
> same? Just checking the assumptions being made and being on the same page with
> them.

I would expect this to be the same problem we have as regular suspend,
after power off the TSC will have been reset, so resume will have to
somehow bridge that gap. I've no idea if/how it does that.

I remember some BIOSes had crazy TSC ideas for suspend2ram, and we grew
tsc_restore_sched_clock_state() for it.

Playing crazy games like what you're doing just isn't it though.