linux-kernel - Re: [BUG] Linux 5.3-rc1: timer problem on x86-64 (Pentium D)

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Date:   Thu, 25 Jul 2019 10:51:13 +0100
From:   Rui Salvaterra <rsalvaterra@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Daniel Drake <drake@...lessm.com>
Subject: Re: [BUG] Linux 5.3-rc1: timer problem on x86-64 (Pentium D)

Hi, Thomas,

On Thu, 25 Jul 2019 at 10:37, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Duh. Yes, this explains it nicely.
>
> > [    1.123548] clocksource: timekeeping watchdog on CPU1: Marking
> > clocksource 'tsc-early' as unstable because the skew is too large:
> > [    1.123552] clocksource:                       'hpet' wd_now: 33
> > wd_last: 33 mask: ffffffff
>
> The HPET counter check succeeded, but the early enable and the following
> reconfiguration confused it completely. So the HPET is not counting:
>
>         'hpet' wd_now: 33 wd_last: 33 mask: ffffffff
>
> Which is a full explanation for the boot fail because if the counter is not
> working then the HPET timer is not expiring and the early boot is waiting
> for HPET to fire forever.

Interesting. Thanks for the detailed explanation!

> That's consistent with the above. 5.3-rc1 unpatched would of course boot as
> well with hpet=disable now that we know the root cause.

I guess that's the only thing I hadn't tried, hindsight is 20/20. :)

> I'll write a changelog and route it to Linus for -rc2.
>
> Thanks a lot for debugging this and providing all the information!

My pleasure! I'm glad to have this old workhorse chugging along again.

Thanks,
Rui