linux-kernel - Re: [PATCH v12 09/11] x86/tsc: prepare for early sched

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Date:   Mon, 2 Jul 2018 13:18:36 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>, jgross@...e.com
Cc:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux@...linux.org.uk, Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
        douly.fnst@...fujitsu.com, Peter Zijlstra <peterz@...radead.org>,
        Prarit Bhargava <prarit@...hat.com>, feng.tang@...el.com,
        Petr Mladek <pmladek@...e.com>, gnomes@...rguk.ukuu.org.uk,
        linux-s390@...r.kernel.org, andriy.shevchenko@...ux.intel.com,
        boris.ostrovsky@...cle.com, pbonzini@...hat.com,
        xen-devel@...ts.xensource.com
Subject: Re: [PATCH v12 09/11] x86/tsc: prepare for early sched_clock

On Fri, Jun 29, 2018 at 09:30:10AM +0200, Thomas Gleixner wrote:
> On Thu, 28 Jun 2018, Pavel Tatashin wrote:
> > On Thu, Jun 28, 2018 at 11:23 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> > Hi Thomas,
> > 
> > In addition to above, we have xen hvm:
> > 
> > setup_arch()
> >     ...
> >     init_hypervisor_platform();
> >         x86_init.hyper.init_platform();
> >             xen_hvm_guest_init()
> >                 xen_hvm_init_time_ops();
> 
> Duh. Missed that completely.
> 
> >     ...
> >     tsc_early_delay_calibrate();
> >         tsc_khz = x86_platform.calibrate_tsc(); == xen_tsc_khz()
> >     ...
> > 
> > Which works early.
> > 
> > So, what should we do with xen, which seems to be the only platform
> > that would provide different tsc frequency early and late, because of
> > different calibration method?
> 
> Fix it? I have no idea why XEN has two variants of the scheme and I neither
> have a clue why the KVM clock stuff is late.

Added Juergen (Xen).
> 
> Thanks,
> 
> 	tglx
>