linux-kernel - Re: [PATCH 6/7] xen: Enable PV clocksource for HVM

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Date:	Fri, 5 Mar 2010 10:54:50 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Keir Fraser <Keir.Fraser@...citrix.com>,
	Ingo Molnar <mingo@...e.hu>,
	Ian Pratt <Ian.Pratt@...citrix.com>,
	Ian Campbell <Ian.Campbell@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 6/7] xen: Enable PV clocksource for HVM

On Friday 05 March 2010 01:40:51 Jeremy Fitzhardinge wrote:
> On 03/04/2010 01:36 AM, Sheng Yang wrote:
> > And enable it by default in PV extended HVM guest.
> >
> > Signed-off-by: Sheng Yang<sheng@...ux.intel.com>
> > ---
> >   arch/x86/xen/hvmpv.c |   20 ++++++++++++++++++++
> >   arch/x86/xen/time.c  |    4 +++-
> >   2 files changed, 23 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/xen/hvmpv.c b/arch/x86/xen/hvmpv.c
> > index 7a741ed..284e021 100644
> > --- a/arch/x86/xen/hvmpv.c
> > +++ b/arch/x86/xen/hvmpv.c
> > @@ -43,6 +43,7 @@ static void __init xen_hvm_pv_banner(void)
> >   		pv_info.name);
> >   	printk(KERN_INFO "Xen version: %d.%d%s\n",
> >   		version>>  16, version&  0xffff, extra.extraversion);
> > +	printk(KERN_INFO "PV feature: PV clocksource enabled\n");
> >   }
> >
> >   static int __init xen_para_available(void)
> > @@ -117,6 +118,22 @@ static void __init init_shared_info(void)
> >   	per_cpu(xen_vcpu, 0) =&HYPERVISOR_shared_info->vcpu_info[0];
> >   }
> >
> > +extern struct clocksource xen_clocksource;
> 
> No externs in .c files.  But aside from that, I'd prefer you export a
> function from xen/time.c to do the clocksource registration and call it
> from both places (even if its a one-liner).

OK
> 
> > +
> > +static void __init init_pv_clocksource(void)
> > +{
> > +	if (enable_hvm_pv(HVM_PV_CLOCK))
> > +		BUG();
> 
> BUG is a bit severe.  Will it really never, ever fail?  And if it does,
> the consequence is hardly serious; we just fall back to emulated devices.

It shouldn't fail. If we got a hypervisor without these extension, this one 
won't be called. Because the feature should be detected by CPUID, and the 
hypervisor would mask the unsupported features. So the guest won't see that 
bit if it's not supported, and this one wouldn't be involved.

-- 
regards
Yang, Sheng

> 
> > +
> > +	pv_time_ops.sched_clock = xen_sched_clock;
> > +
> > +	x86_platform.calibrate_tsc = xen_tsc_khz;
> > +	x86_platform.get_wallclock = xen_get_wallclock;
> > +	x86_platform.set_wallclock = xen_set_wallclock;
> > +
> > +	clocksource_register(&xen_clocksource);
> > +}
> > +
> >   void __init xen_guest_init(void)
> >   {
> >   	int r;
> > @@ -130,4 +147,7 @@ void __init xen_guest_init(void)
> >   		return;
> >
> >   	init_shared_info();
> > +
> > +	/* PV clocksource would be enabled by default */
> > +	init_pv_clocksource();
> >   }
> > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> > index 0d3f07c..c80eacb 100644
> > --- a/arch/x86/xen/time.c
> > +++ b/arch/x86/xen/time.c
> > @@ -13,6 +13,7 @@
> >   #include<linux/clockchips.h>
> >   #include<linux/kernel_stat.h>
> >   #include<linux/math64.h>
> > +#include<linux/module.h>
> >
> >   #include<asm/pvclock.h>
> >   #include<asm/xen/hypervisor.h>
> > @@ -243,7 +244,7 @@ int xen_set_wallclock(unsigned long now)
> >   	return -1;
> >   }
> >
> > -static struct clocksource xen_clocksource __read_mostly = {
> > +struct clocksource xen_clocksource __read_mostly = {
> >   	.name = "xen",
> >   	.rating = 400,
> >   	.read = xen_clocksource_get_cycles,
> > @@ -252,6 +253,7 @@ static struct clocksource xen_clocksource
> > __read_mostly = { .shift = XEN_SHIFT,
> >   	.flags = CLOCK_SOURCE_IS_CONTINUOUS,
> >   };
> > +EXPORT_SYMBOL_GPL(xen_clocksource);
> >
> >   /*
> >      Xen clockevent implementation
> 
--
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