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Date: Mon, 2 Jul 2018 13:18:36 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH v12 09/11] x86/tsc: prepare for early sched_clock
Message-ID: <20180702171836.GD22876@char.us.oracle.com>
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To: Thomas Gleixner <tglx@linutronix.de>, jgross@suse.com
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>, Steven Sistare <steven.sistare@oracle.com>, Daniel Jordan <daniel.m.jordan@oracle.com>, linux@armlinux.org.uk, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <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, "H. Peter Anvin" <hpa@zytor.com>, douly.fnst@cn.fujitsu.com, Peter Zijlstra <peterz@infradead.org>, Prarit Bhargava <prarit@redhat.com>, feng.tang@intel.com, Petr Mladek <pmladek@suse.com>, gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org, andriy.shevchenko@linux.intel.com, boris.ostrovsky@oracle.com, pbonzini@redhat.com, xen-devel@lists.xensource.com
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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@linutronix.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
>