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

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 17-07-04 01:28:32, Jan Beulich wrote:
> >>> On 04.07.17 at 03:40, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > On 17-06-30 03:18:53, Jan Beulich wrote:
> >> >>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/30/17 10:05 AM >>>
> >> >On 17-06-30 01:33:02, Jan Beulich wrote:
> >> >> >>> Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx> 06/30/17 9:01 AM >>>
> > There will be problem if we substract 1 before doing the shift for the even
> > number. E.g. the original cos_max is 2, (2-1)>>1 will be 0. That is not we
> > want. For the odd number, direct right shift is good too. E.g. the original
> > cos_max is 3, 3 >> 1 is 1 which is what we want.
> 
> What we want is
> 
>       raw     CDP
>       0       unusable
>       1       0
>       2       0
>       3       1
>       4       1
>       5       2
>       6       2
> 
> Other than what you say, for original cos_max = 2 we indeed need
> to convert it to 0, or else CDP would use indexes 2 ( = 1 * 2 + 0)
> and 3 ( = 1 * 2 + 1), exceeding the mandated upper bound.
> 
> >> insufficient for the CDP case?
> > 
> > We do not need check if cos_max > 1 because the 'cos_max = 0' works for us.
> > That means only COS ID 0 can be used. You can see, we use "cos <= cos_max" 
> > to
> > find COS ID. Of course, the ID 0 saves the default value which cannot be
> > overwritten.
> 
> Please see the (current) check in init_psr_cat(), which your series
> moves into init_psr(). Logically in the CDP case we should require
> cos_max >= 3 to have at least one usable COS ID.
> 
> Jan

Thank you! You are right. I will modify codes to do so.

BRs,
Sun Yi

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