linux-kernel - Re: [PATCH] raise tsc clocksource rating

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Message-ID: <alpine.LFD.0.9999.0710292315280.3186@localhost.localdomain>
Date:	Mon, 29 Oct 2007 23:17:38 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Glauber de Oliveira Costa <gcosta@...hat.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>, --cc@...hat.com,
	Ingo Molnar <mingo@...e.hu>, avi@...amnet.com,
	kvm-devel@...ts.sourceforge.net, John Stultz <johnstul@...ibm.com>
Subject: Re: [PATCH] raise tsc clocksource rating

On Mon, 29 Oct 2007, Glauber de Oliveira Costa wrote:

CC'ed John and removed glauber@....localdomain :)

> From: Glauber de Oliveira Costa <glauber@....localdomain>
> 
> tsc is very good time source (when it does not have drifts, does not
> change it's frequency, i.e. when it works), so it should have its rating
> raised to a value greater than, or equal 400.
> 
> Since it's being a tendency among paravirt clocksources to use values
> around 400, we should declare tsc as even better: So we use 500.
> 
> This patch also touches the comments on clocksource.h, which suggests
> that 499 would be a limit on the rating values.
> 
> Signed-off-by: Glauber de Oliveira Costa <gcosta@...hat.com>

Acked-by: Thomas Gleixner <tglx@...utronix.de>

> ---
>  arch/x86/kernel/tsc_32.c    |    2 +-
>  arch/x86/kernel/tsc_64.c    |    2 +-
>  include/linux/clocksource.h |    2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
> index 9ebc0da..4d91e59 100644
> --- a/arch/x86/kernel/tsc_32.c
> +++ b/arch/x86/kernel/tsc_32.c
> @@ -280,7 +280,7 @@ static cycle_t read_tsc(void)
>  
>  static struct clocksource clocksource_tsc = {
>  	.name			= "tsc",
> -	.rating			= 300,
> +	.rating			= 500,
>  	.read			= read_tsc,
>  	.mask			= CLOCKSOURCE_MASK(64),
>  	.mult			= 0, /* to be set */
> diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c
> index 9c70af4..4fd5b1b 100644
> --- a/arch/x86/kernel/tsc_64.c
> +++ b/arch/x86/kernel/tsc_64.c
> @@ -262,7 +262,7 @@ static cycle_t __vsyscall_fn vread_tsc(void)
>  
>  static struct clocksource clocksource_tsc = {
>  	.name			= "tsc",
> -	.rating			= 300,
> +	.rating			= 500,
>  	.read			= read_tsc,
>  	.mask			= CLOCKSOURCE_MASK(64),
>  	.shift			= 22,
> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> index 107787a..5b0aadd 100644
> --- a/include/linux/clocksource.h
> +++ b/include/linux/clocksource.h
> @@ -39,7 +39,7 @@ struct clocksource;
>   *				A correct and usable clocksource.
>   *			300-399: Desired.
>   *				A reasonably fast and accurate clocksource.
> - *			400-499: Perfect
> + *			>= 400 : Perfect
>   *				The ideal clocksource. A must-use where
>   *				available.
>   * @read:		returns a cycle value
> -- 
> 1.5.0.6
> 
> -
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