linux-kernel - RE: [PATCH 1/1] x86: Hyper-V: Mark the Hyper-V clocksource as being high resolution

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Message-ID: <BY2PR0301MB16542BA56C8CACAE01722BF6A0950@BY2PR0301MB1654.namprd03.prod.outlook.com>
Date:	Sat, 4 Jul 2015 16:11:35 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Thomas Gleixner <tglx@...utronix.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>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	Vivek Yadav <vyadav@...rosoft.com>
Subject: RE: [PATCH 1/1] x86: Hyper-V: Mark the Hyper-V clocksource as being
 high resolution



> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Saturday, July 4, 2015 1:11 AM
> To: KY Srinivasan
> Cc: x86@...nel.org; gregkh@...uxfoundation.org; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> apw@...onical.com; jasowang@...hat.com; Vivek Yadav
> Subject: Re: [PATCH 1/1] x86: Hyper-V: Mark the Hyper-V clocksource as
> being high resolution
> 
> On Fri, 3 Jul 2015, K. Y. Srinivasan wrote:
> > From: Vivek yadav <vyadav@...rosoft.com>
> >
> > By design, alternative clock sources listed are based on the resolution of
> > current clock source. Once you set a  high resolution clock,
> > only high resolution sources are returned.
> > Mark Hyper-V clock source as a high resolution clock source.
> >
> > Signed-off-by: Vivek yadav <vyadav@...rosoft.com>
> > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > ---
> >  arch/x86/kernel/cpu/mshyperv.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c
> b/arch/x86/kernel/cpu/mshyperv.c
> > index 9b5d7b5..0e507a0 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -151,7 +151,8 @@ static struct clocksource hyperv_cs = {
> >  	.rating		= 400, /* use this when running on Hyperv*/
> >  	.read		= read_hv_clock,
> >  	.mask		= CLOCKSOURCE_MASK(64),
> > -	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
> > +	.flags		= CLOCK_SOURCE_IS_CONTINUOUS |
> > +			  CLOCK_SOURCE_VALID_FOR_HRES,
> 
> No, this is wrong. The CLOCK_SOURCE_VALID_FOR_HRES flag is managed by
> the core code and set when a clocksource fulfils the criteria.
> 
> The changelog above is not explaining what problem you are trying to
> solve.
> 

I think the problem Vivek was trying to solve is that after the Hyper-V clocxk was
installed, if the user switched to another clocksource,  say tsc, the hyper-V clock source would not
listed. I will investigate this further and let you know. Thanks for the feedback.

Regards,

K. Y 
> 
> 	tglx
> 

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