Re: [Xen-devel] [PATCH v12 13/23] x86: refactor psr: CDP: implement CPU init flow.

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/30/17 9:01 AM >>>
>On 17-06-30 00:40:35, Jan Beulich wrote:
>> >>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/14/17 3:26 AM >>>
>> > @@ -253,6 +271,26 @@ static void cat_init_feature(const struct cpuid_leaf 
>> > *regs,
>> >  
>> >          break;
>> >  
>> > +    case PSR_SOCKET_L3_CDP:
>> > +    {
>> > +        uint64_t val;
>> > +
>> > +        /* Cut half of cos_max when CDP is enabled. */
>> > +        feat->cos_max >>= 1;
>> 
>> I'm afraid this is off by one in the unusual but possible case of cos_max
>> being an even number.
>> 
>This accords to spec:
>"For CDP operations, COS_MAX_CDP is equal to (CPUID.(EAX=10H, 
>ECX=1):EDX.COS_MAX_CAT >>1)."
>
>HW should make sure it is even number.

And how about someone using the command line option to shrink the to be used 
set?

Jan


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