Re: [Xen-devel] [PATCH v3 04/13] x86/time.c: Scale host TSC in pvclock properly

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.01.16 at 14:22, <haozhong.zhang@xxxxxxxxx> wrote:
> On 01/08/16 02:20, Jan Beulich wrote:
>> >>> On 31.12.15 at 04:03, <haozhong.zhang@xxxxxxxxx> wrote:
>> > --- a/xen/arch/x86/time.c
>> > +++ b/xen/arch/x86/time.c
>> > @@ -815,10 +815,18 @@ static void __update_vcpu_system_time(struct vcpu 
>> > *v, int force)
>> >      }
>> >      else
>> >      {
>> > -        tsc_stamp = t->local_tsc_stamp;
>> > -
>> > -        _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
>> > -        _u.tsc_shift         = (s8)t->tsc_scale.shift;
>> > +        if ( has_hvm_container_domain(d) && cpu_has_tsc_ratio )
>> 
>> For symmetry with patches 1 and 2 I'd expect !d->arch.vtsc to be
>> added here too.
> 
> even though it's already in the !d->arch.vtsc branch? But I'm fine to
> add it for symmetric.

Ah, no, I didn't realize (only looking at the patch) that it's in the
else to a respective if(). No need to change it then.

>> > +        {
>> > +            tsc_stamp            = hvm_funcs.scale_tsc(v, 
> t->local_tsc_stamp);
>> > +            _u.tsc_to_system_mul = d->arch.vtsc_to_ns.mul_frac;
>> > +            _u.tsc_shift         = d->arch.vtsc_to_ns.shift;
>> > +        }
>> > +        else
>> > +        {
>> > +            tsc_stamp            = t->local_tsc_stamp;
>> > +            _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
>> > +            _u.tsc_shift         = (s8)t->tsc_scale.shift;
>> 
>> The case has been pointless anyway, and you don't add a similar
>> one in the if() branch - please delete it.
> 
> I don't understand why it's pointless. The inner if branch is to
> ensure pvclock provides the scaled TSC information when TSC scaling is
> used, and the inner else branch is to keep the existing behavior when
> TSC scaling is not used. For the outer if branch, TSC scaling is never
> used, so no change is needed.

Sorry, I see I typo-ed my reply. It was meant to start "The cast
has been ..."

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel