Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sat, 26 Jan 2019 16:11:37 +0000
From:   Pavel Tatashin <pasha.tatashin@soleen.com>
To:     Dominique Martinet <asmadeus@codewreck.org>,
        Salvatore Bonaccorso <carnil@debian.org>,
        Steven Sistare <steven.sistare@oracle.com>,
        Pavel Tatashin <pavel.tatashin@microsoft.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        linux@armlinux.org.uk, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, John Stultz <john.stultz@linaro.org>,
        sboyd@codeaurora.org, x86@kernel.org,
        LKML <linux-kernel@vger.kernel.org>, mingo@redhat.com,
        Thomas Gleixner <tglx@linutronix.de>, hpa@zytor.com,
        douly.fnst@cn.fujitsu.com, Peter Zijlstra <peterz@infradead.org>,
        prarit@redhat.com, feng.tang@intel.com,
        Petr Mladek <pmladek@suse.com>, gnomes@lxorguk.ukuu.org.uk,
        linux-s390@vger.kernel.org, boris.ostrovsky@oracle.com,
        jgross@suse.com, pbonzini@redhat.com,
        virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
        qemu-devel@nongnu.org
Subject: Re: [PATCH v15 23/26] sched: early boot clock
Message-ID: <20190126161137.gme4vsrz3xmncbkx@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net>
References: <20180719205545.16512-24-pasha.tatashin@oracle.com>
 <20181106054212.GA31768@nautica>
 <95c3920e-bf80-0c7e-7854-01a1c3189c23@oracle.com>
 <20190102202032.GA1034@eldamar.local>
 <CA+CK2bC70pnL0Wimb0xt99J4nNfi8W3zuUHgAk-jsPuOP9jpHA@mail.gmail.com>
 <20190103234339.GA17457@nautica>
 <CA+CK2bDj1f=VpT+k-e8kSSaoLJ3W9-JPPq9udFdDwd6ijXi28g@mail.gmail.com>
 <20190107234839.GA15269@nautica>
 <CA+CK2bD3kbcNvkVf2kiKQYs+srcw7BdWngqt_wM7Z-QsBJyH6w@mail.gmail.com>
 <20190126020410.GB3796@feynman.vault24.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190126020410.GB3796@feynman.vault24.org>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 19-01-25 21:04:10, Jon DeVree wrote:
> 
> * KVM_FEATURE_CLOCKSOURCE_STABLE_BIT is always set by the hypervisor
>   starting with Linux v2.6.35 - 371bcf646d17 ("KVM: x86: Tell the guest
>   we'll warn it about tsc stability")
> * PVCLOCK_TSC_STABLE_BIT is set starting in Linux v3.8 but only if the
>   clocksource is the TSC - d828199e8444 ("KVM: x86: implement
>   PVCLOCK_TSC_STABLE_BIT pvclock flag")
> 
> I changed the clocksource of a hypervisor that wasn't having issues from
> TSC to HPET and when I started up a guest VM the bug suddenly appeared.
> I shut down the guest, set the hypervisor's clocksource back to TSC,
> started up the guest and the bug went away again.
> 
> You don't actually have to reboot the guest before the bug is visible
> either, just letting the guest sit at the GRUB menu for a minute or two
> before loading Linux is enough to make the bug plainly visible in the
> printk timestamps.
> 
> I don't know enough to actually fix the bug, but hopefully this is
> enough to allow everyone else to reproduce it and come up with a fix.

Thank you very much for your analysis, I am now able to reproduce the
problem by setting clocksource on my machine to hpet. I will soon submit a
patch with a fix.

Pasha

> 
> -- 
> Jon
> X(7): A program for managing terminal windows. See also screen(1) and tmux(1).