linux-kernel - RE: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency from the hypervisor

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Message-ID: <418dd0e9b1054189b61770edb57c5b37@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Fri, 27 Sep 2013 15:23:17 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Olaf Hering <olaf@...fle.de>
CC:	"x86@...nel.org" <x86@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"JBeulich@...e.com" <JBeulich@...e.com>,
	"bp@...en8.de" <bp@...en8.de>
Subject: RE: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency
 from the hypervisor



> -----Original Message-----
> From: Olaf Hering [mailto:olaf@...fle.de]
> Sent: Friday, September 27, 2013 8:10 AM
> To: KY Srinivasan
> Cc: x86@...nel.org; gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; apw@...onical.com; jasowang@...hat.com;
> tglx@...utronix.de; hpa@...or.com; JBeulich@...e.com; bp@...en8.de
> Subject: Re: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency
> from the hypervisor
> 
> On Tue, Sep 03, K. Y. Srinivasan wrote:
> 
> > Hyper-V supports a mechanism for retrieving the local APIC frequency.Use this
> and bypass
> > the calibration code in the kernel. This would allow us to boot the Linux kernel
> as a
> > "modern VM" on Hyper-V where many of the legacy devices (such as PIT) are
> not emulated.
> 
> > +	if (ms_hyperv.features & HV_X64_MSR_APIC_FREQUENCY_AVAILABLE) {
> > +		/*
> > +		 * Get the APIC frequency.
> > +		 */
> > +		rdmsrl(HV_X64_MSR_APIC_FREQUENCY, hv_lapic_frequency);
> > +		hv_lapic_frequency /= HZ;
> 
> This leads to build errors on 32bit:
> 
> linux-3.12-rc2/arch/x86/kernel/cpu/mshyperv.c:88: undefined reference to
> `__udivdi3'
> 
> Up to now I have only tested on 64bit, sorry for that.

Thanks Olaf. I am travelling currently; I will fix it when I get back (early next week).

K. Y
> 
> 
> Olaf