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

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Message-ID: <alpine.DEB.2.11.1507041008290.3916@nanos>
Date:	Sat, 4 Jul 2015 10:10:32 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
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 <vyadav@...rosoft.com>
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.

Thanks,

	tglx


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