linux-kernel - Re: [patch] paravirt: allow NO_HZ, remove NO_IDLE

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Date:	Mon, 05 Mar 2007 12:46:45 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [patch] paravirt: allow NO_HZ, remove NO_IDLE_HZ dependency

On Mon, 2007-03-05 at 12:29 +0100, Ingo Molnar wrote:
> Subject: [patch] paravirt: remove NO_IDLE_HZ dependency
> From: Ingo Molnar <mingo@...e.hu>
> 
> PARAVIRT forces CONFIG_NO_HZ off - this is bad and prevents sane 
> paravirtual guests like KVM from being able to use dynticks-enabled 
> Linux guests. Remove this. Vmi-timer needs to be updated properly to 
> make use of dynticks.
> 
> furthermore, remove the mistaken turning on of NO_IDLE_HZ on 
> x86+PARAVIRT kernels, it's an obsolete, limited form of dynticks.
> 
> must-have for v2.6.21.
> 
> Signed-off-by: Ingo Molnar <mingo@...e.hu>

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

> ---
>  arch/i386/Kconfig |   11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> Index: linux/arch/i386/Kconfig
> ===================================================================
> --- linux.orig/arch/i386/Kconfig
> +++ linux/arch/i386/Kconfig
> @@ -224,7 +224,7 @@ config PARAVIRT
>  
>  config VMI
>  	bool "VMI Paravirt-ops support"
> -	depends on PARAVIRT && !NO_HZ
> +	depends on PARAVIRT
>  	default y
>  	help
>  	  VMI provides a paravirtualized interface to multiple hypervisors
> @@ -1291,12 +1291,3 @@ config X86_TRAMPOLINE
>  config KTIME_SCALAR
>  	bool
>  	default y
> -
> -config NO_IDLE_HZ
> -	bool
> -	depends on PARAVIRT
> -	default y
> -	help
> -	  Switches the regular HZ timer off when the system is going idle.
> -	  This helps a hypervisor detect that the Linux system is idle,
> -	  reducing the overhead of idle systems.

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