From: Miklos Szeredi <miklos@szeredi.hu>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Juergen Gross <jgross@suse.com>,
linux-kernel@vger.kernel.org
Subject: Re: system time goes weird in kvm guest after host suspend/resume
Date: Thu, 4 Jun 2020 21:28:57 +0200 [thread overview]
Message-ID: <CAJfpegvchB2H=NK3JU0BQS7h=kXyifgKD=JHjjT6vTYVMspY2A@mail.gmail.com> (raw)
In-Reply-To: <87367a91rn.fsf@nanos.tec.linutronix.de>
On Thu, Jun 4, 2020 at 7:30 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Miklos,
>
> Thomas Gleixner <tglx@linutronix.de> writes:
> >> Of course this does not reproduce here. What kind of host is this
> >> running on? Can you provide a full demsg of the host please from boot to
> >> post resume?
> >
> > Plus /proc/cpuinfo please (one CPU is sufficient)
>
> thanks for providing the data. Unfortunately not really helpful. The
> host has a non-stop TSC and the dmesg does not contain anything which
> sheds light on this.
>
> I grabbed a similar machine, installed a guest with 5.7 kernel and I'm
> still unable to reproduce. No idea yet how to get down to the real root
> cause of this.
Well, I have neither. But more investigation turned up some interesting things.
time(2) returns good time, while clock_gettime(2) returns bad time.
Here's an example:
time=1591298725 RT=1591300383 MONO=39582 MONO_RAW=39582 BOOT=39582
time=1591298726 RT=1591300383 MONO=39582 MONO_RAW=39582 BOOT=39582
time=1591298727 RT=1591300383 MONO=39582 MONO_RAW=39582 BOOT=39582
time=1591298728 RT=1591300383 MONO=39582 MONO_RAW=39582 BOOT=39582
time=1591298729 RT=1591300383 MONO=39582 MONO_RAW=39582 BOOT=39582
As you can see, only time(2) is updated, the others remain the same.
date(1) uses clock_gettime(CLOCK_REALTIME) so that shows the bad date.
When the correct time reaches the value returned by CLOCK_REALTIME,
the value jumps exactly 2199 seconds.
Does that make any sense?
Thanks,
Miklos
next prev parent reply other threads:[~2020-06-04 19:29 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 19:45 system time goes weird in kvm guest after host suspend/resume Miklos Szeredi
2020-05-28 20:43 ` Thomas Gleixner
2020-05-29 9:51 ` Miklos Szeredi
2020-05-29 9:57 ` Miklos Szeredi
2020-05-29 12:21 ` Thomas Gleixner
2020-05-29 12:31 ` Miklos Szeredi
2020-05-29 12:33 ` Miklos Szeredi
2020-06-03 15:41 ` Thomas Gleixner
2020-06-03 15:45 ` Thomas Gleixner
2020-06-04 17:30 ` Thomas Gleixner
2020-06-04 19:28 ` Miklos Szeredi [this message]
2020-06-04 20:14 ` Paolo Bonzini
2020-06-05 7:35 ` Miklos Szeredi
2020-06-05 8:09 ` Paolo Bonzini
2020-06-05 10:11 ` Thomas Gleixner
2020-06-05 10:21 ` Miklos Szeredi
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