linux-kernel - Re: [PATCH] x86 kconfig: Add recommendation to enable paravirt spinlock

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Message-ID: <20131021163038.GA17709@phenom.dumpdata.com>
Date:	Mon, 21 Oct 2013 12:30:38 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	mingo@...hat.com, hpa@...or.com, x86@...nel.org, gleb@...hat.com,
	pbonzini@...hat.com, tglx@...utronix.de, linux@...elenboom.it,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86 kconfig: Add recommendation to enable paravirt
 spinlock

On Mon, Oct 21, 2013 at 09:35:08PM +0530, Raghavendra K T wrote:
> Since paravirt spinlock optimization are in 3.12 kernel, we have
> very good performance benefit for paravirtualized KVM / Xen kernel.
> Also we no longer suffer from 5% side effect on native kernel.

Yeey!
> 
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> ---
>  Would like to thank Sander for spotting and suggesting this.
>  pvspinlock benefit on KVM link: https://lkml.org/lkml/2013/8/6/178 
>  
>  Attilio's tests on native kernel impact:
>  http://blog.xen.org/index.php/2012/05/11/benchmarking-the-new-pv-ticketlock-implementation/
> 
>  arch/x86/Kconfig | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f67e839..4ba9d32 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -638,10 +638,10 @@ config PARAVIRT_SPINLOCKS
>  	  spinlock implementation with something virtualization-friendly
>  	  (for example, block the virtual CPU rather than spinning).
>  
> -	  Unfortunately the downside is an up to 5% performance hit on
> -	  native kernels, with various workloads.
> +	  It has minimal impact on native kernels and gives nice performance
> +	  benefit for paravirtualized KVM / Xen kernels.
>  
> -	  If you are unsure how to answer this question, answer N.
> +	  If you are unsure how to answer this question, answer Y.
>  
>  source "arch/x86/xen/Kconfig"
>  
> -- 
> 1.7.11.7
> 
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