RE: [Xen-devel] RE: question about hvm vhpet

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Agreed.... at least unless/until Dave Winchell's hpet
work gets resubmitted and accepted, hpet is not reliable
as a timer for most guests.  And some OS's will
always automatically choose hpet if it is enabled
even, in some cases, if another clocksource was intended.

So off is better... but we should be aware that turning
it off may provoke significant timer issues for some
customers who upgrade.  The ideal solution is to get
Dave's code in and leave the vhpet default to on, but
I don't think Dave has had any time to work on this
(and I haven't had time either).

Dan

P.S. IIRC, a new timer_mode needs to be added that ensures
that two ticks are never delivered too close together,
as this will cause time to run too fast.

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> Sent: Friday, November 21, 2008 1:10 AM
> To: Tian, Kevin; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] RE: question about hvm vhpet
> 
> 
> >From: Tian, Kevin
> >Sent: Friday, November 21, 2008 2:59 PM
> >
> >I'm a bit confused whether vhpet is enabled by default or not.
> >
> >Per 17017, changelog says vhpet disabled by default, but the code
> >conflicts as below:
> >@@ -231,6 +231,8 @@ int hvm_domain_initialise(struct domain
> >     spin_lock_init(&d->arch.hvm_domain.pbuf_lock);
> >     spin_lock_init(&d->arch.hvm_domain.irq_lock);
> >     spin_lock_init(&d->arch.hvm_domain.uc_lock);
> >+
> >+    d->arch.hvm_domain.params[HVM_PARAM_HPET_ENABLED] = 1;
> >
> >Then if config file for hvm domain has no explicit 'hpet=0/1' option,
> >will xend issue a hypercall to set vhpet to '0' or the latter will be
> >left as '1'?
> >
> 
> It's the former. Anyway, let's keep code aligned with original
> purpose.
> ----
> Disable vhpet for hvm domain by default.
> 
> Signed-off-by Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> diff -r c70317be929c xen/arch/x86/hvm/hvm.c
> --- a/xen/arch/x86/hvm/hvm.c    Fri Nov 21 07:39:30 2008 +0800
> +++ b/xen/arch/x86/hvm/hvm.c    Fri Nov 21 07:40:01 2008 +0800
> @@ -305,8 +305,6 @@ int hvm_domain_initialise(struct domain
> 
>      hvm_init_guest_time(d);
> 
> -    d->arch.hvm_domain.params[HVM_PARAM_HPET_ENABLED] = 1;
> -
>      hvm_init_cacheattr_region_list(d);
> 
>      rc = paging_enable(d, PG_refcounts|PG_translate|PG_external);
> 
> Thanks,
> Kevin
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> http://lists.xensource.com/xen-devel
>

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