linux-kernel - Re: [patch 0/2] tsc/adjust: Cure suspend/resume issues and prevent TSC deadline timer irq storm

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Date:   Thu, 15 Dec 2016 10:31:27 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Roland Scheidegger <rscheidegger_lists@...peed.ch>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Kevin Stanton <kevin.b.stanton@...el.com>,
        Allen Hung <allen_hung@...l.com>
Subject: Re: [patch 0/2] tsc/adjust: Cure suspend/resume issues and prevent
 TSC deadline timer irq storm

On Wed, 14 Dec 2016, Roland Scheidegger wrote:
> Am 14.12.2016 um 22:40 schrieb Thomas Gleixner:
> > And the whole mess stems from the fact that the deadline is not as one
> > would expect simply compared against the sum of the counter and the adjust
> > MSR.
> Why would it be compared against the sum? As far as I can tell the adjust
> value should never come into play when using deadline timer (other than
> indirectly because the TSC would change).

See the SDM. It suggests that the deadline is compared to the TSC value.

I don't care how it is implemented, but I very much care about it being
documented in the way it is implemented, which is obviously not the case.

And even if the adjust value is subtracted once when the timer is armed the
whole thing should not blow up due to 32bit/sign extension bugs or whatever
they decided to cobble together.

Thanks,

	tglx