Re: [Xen-devel] [PATCH v4 1/3] x86: Use native RDTSC(P) execution when guest and host frequencies are the same

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.04.14 at 16:28, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 04/16/2014 07:38 AM, Jan Beulich wrote:
>>>>> On 16.04.14 at 03:27, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> @@ -1889,10 +1890,14 @@ void tsc_set_info(struct domain *d,
>>>           d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
>>>           d->arch.tsc_khz = gtsc_khz ? gtsc_khz : cpu_khz;
>>>           set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
>>> -        /* use native TSC if initial host has safe TSC, has not migrated
>>> -         * yet and tsc_khz == cpu_khz */
>>> -        if ( host_tsc_is_safe() && incarnation == 0 &&
>>> -                d->arch.tsc_khz == cpu_khz )
>>> +        /*
>>> +         * Use native TSC if initial host has safe TSC and either has not
>>> +         * migrated yet or tsc_khz == cpu_khz (either "naturally" or via
>>> +         * TSC scaling)
>>> +         */
>>> +        if ( host_tsc_is_safe() &&
>>> +             (incarnation == 0 || d->arch.tsc_khz == cpu_khz ||
>>> +              cpu_has_tsc_ratio) )
>> Doesn't this cpu_has_tsc_ratio check also need to be qualified with
>> is_pv_domain()? And is the change from && in the old condition to ||
>> actually valid for PV guests?
> 
> Hmm, I haven't thought about PV here.
> 
> So then the condition should be
> 
> if ( host_tsc_is_safe() )
> {
>      if ( (is_hvm_domain() && (arch.tsc_khz == cpu_khz || cpu_has_tsc_ratio)) 
> ||
>            (incarnation == 0 && d->arch.tsc_khz == cpu_khz) )
>                d->arch.vtsc = 0;
> }

Almost - to include PVH you need to either use !is_pv_domain() or
has_hvm_container_domain().

Jan


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