Re: [PATCH 10/11] Support VIRQ_TIMER and pvclock on HVM

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 05/24/2010 11:27 AM, Stefano Stabellini wrote:
> Use the paravirtualized timer (VIRQ_TIMER) as timer and the
> paravirtualized clock (pvclock) as wallclock on HVM domains too.
>   

That's not quite correct.  There's the Xen clockevent driver, the Xen
clocksource, and a distinct-but-related Xen notion of wallclock time. 
In general, clocksources and wallclock don't have much direct
relationship to each other.

> Any interaction with emulated hardware is not very fast, so using the
> paravirtualized timer instead of the emulated hpet is defenitely a
>   
"definitely"

> performance improvement.
>   

Are there accuracy/stability/precision improvements too?

    J

> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  arch/x86/xen/enlighten.c         |   31 +++++++++++++++++++++++++++++++
>  arch/x86/xen/suspend.c           |    4 ++++
>  include/xen/interface/features.h |    3 +++
>  3 files changed, 38 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index cb316b5..88e8a09 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1307,6 +1307,36 @@ static struct notifier_block __cpuinitdata xen_hvm_cpu_notifier = {
>  	.notifier_call	= xen_hvm_cpu_notify,
>  };
>  
> +static void xen_hvm_setup_cpu_clockevents(void)
> +{
> +	int cpu = smp_processor_id();
> +	xen_setup_runstate_info(cpu);
> +	xen_setup_timer(cpu);
> +	xen_setup_cpu_clockevents();
> +}
> +
> +static void init_hvm_time(void)
> +{
> +	/* vector callback is needed otherwise we cannot receive interrupts
> +	 * on cpu > 0 */
> +	if (!xen_have_vector_callback && num_present_cpus() > 1)
> +		return;
> +	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {
> +		printk(KERN_INFO "Xen doesn't support pvclock on HVM,"
> +				"disable pv timer\n");
> +		return;
> +	}
> +
> +	pv_time_ops = xen_time_ops;
> +	x86_init.timers.timer_init = xen_time_init;
> +	x86_init.timers.setup_percpu_clockev = x86_init_noop;
> +	x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;
> +
> +	x86_platform.calibrate_tsc = xen_tsc_khz;
> +	x86_platform.get_wallclock = xen_get_wallclock;
> +	x86_platform.set_wallclock = xen_set_wallclock;
> +}
> +
>  void __init xen_guest_init(void)
>  {
>  	int r;
> @@ -1326,4 +1356,5 @@ void __init xen_guest_init(void)
>  	register_cpu_notifier(&xen_hvm_cpu_notifier);
>  	have_vcpu_info_placement = 0;
>  	x86_init.irqs.intr_init = xen_init_IRQ;
> +	init_hvm_time();
>  }
> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> index ef517ee..02c3253 100644
> --- a/arch/x86/xen/suspend.c
> +++ b/arch/x86/xen/suspend.c
> @@ -28,8 +28,12 @@ void xen_pre_suspend(void)
>  
>  void xen_hvm_post_suspend(int suspend_cancelled)
>  {
> +	int cpu;
>  	init_shared_info();
>  	xen_callback_vector();
> +	for_each_online_cpu(cpu) {
> +		xen_setup_runstate_info(cpu);
> +	}
>  }
>  
>  void xen_post_suspend(int suspend_cancelled)
> diff --git a/include/xen/interface/features.h b/include/xen/interface/features.h
> index 8ab08b9..70d2563 100644
> --- a/include/xen/interface/features.h
> +++ b/include/xen/interface/features.h
> @@ -44,6 +44,9 @@
>  /* x86: Does this Xen host support the HVM callback vector type? */
>  #define XENFEAT_hvm_callback_vector        8
>  
> +/* x86: pvclock algorithm is safe to use on HVM */
> +#define XENFEAT_hvm_safe_pvclock           9
> +
>  #define XENFEAT_NR_SUBMAPS 1
>  
>  #endif /* __XEN_PUBLIC_FEATURES_H__ */
>