linux-kernel - Re: [Xen-devel] [PATCH] xen-time: decreasing the rating of the xen clocksource below that of the tsc clocksource for dom0's

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Date:	Tue, 13 Jan 2015 09:52:07 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Imre Palik <imrep.amz@...il.com>, <xen-devel@...ts.xenproject.org>,
	David Vrabel <david.vrabel@...rix.com>
CC:	"Palik, Imre" <imrep@...zon.de>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	Anthony Liguori <aliguori@...zon.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCH] xen-time: decreasing the rating of the xen
 clocksource below that of the tsc clocksource for dom0's

On 13/01/15 08:14, Imre Palik wrote:
> From: "Palik, Imre" <imrep@...zon.de>
> 
> In Dom0's the use of the TSC clocksource (whenever it is stable enough to
> be used) instead of the Xen clocksource should not cause any issues, as
> Dom0 VMs never live-migrated.  The TSC clocksource is somewhat more
> efficient than the Xen paravirtualised clocksource, thus it should have
> higher rating.
> 
> This patch decreases the rating of the Xen clocksource in Dom0s to 275.
> Which is half-way between the rating of the TSC clocksource (300) and the
> hpet clocksource (250).

I'm happy with this but would like to see acks from those who objected
to v1.

David

> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -487,6 +487,10 @@ static void __init xen_time_init(void)
>  	int cpu = smp_processor_id();
>  	struct timespec tp;
>  
> +	/* As Dom0 is never moved, no penalty on using TSC there */
> +	if (xen_initial_domain())
> +		xen_clocksource.rating = 275;
> +
>  	clocksource_register_hz(&xen_clocksource, NSEC_PER_SEC);
>  
>  	if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
> 

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