Re: [Xen-devel] [PATCH v9 10/25] x86: refactor psr: L3 CAT: set value: assemble features value array.

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

On 17-03-28 03:20:05, Jan Beulich wrote:
> >>> On 28.03.17 at 11:11, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> > On 17-03-28 02:36:05, Jan Beulich wrote:
> >> >>> On 28.03.17 at 10:05, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> >> > On 17-03-28 11:12:43, Yi Sun wrote:
> >> >> On 17-03-27 04:17:28, Jan Beulich wrote:
> >> >> > >>> On 16.03.17 at 12:08, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> >> >> > > --- a/xen/arch/x86/psr.c
> >> >> > > +++ b/xen/arch/x86/psr.c
> >> > [...]
> >> > 
> >> >> > >  static int gather_val_array(uint32_t val[],
> >> >> > > @@ -589,7 +672,34 @@ static int gather_val_array(uint32_t val[],
> >> >> > >                              const struct psr_socket_info *info,
> >> >> > >                              unsigned int old_cos)
> >> >> > >  {
> >> >> > > -    return -EINVAL;
> >> >> > > +    const struct feat_node *feat;
> >> >> > > +    unsigned int i;
> >> >> > > +
> >> >> > > +    if ( !val )
> >> >> > > +        return -EINVAL;
> >> >> > > +
> >> >> > > +    /* Get all features current values according to old_cos. */
> >> >> > > +    for ( i = 0; i < PSR_SOCKET_MAX_FEAT; i++ )
> >> >> > > +    {
> >> >> > > +        if ( !info->features[i] )
> >> >> > > +            continue;
> >> >> > > +
> >> >> > > +        feat = info->features[i];
> >> >> > > +
> >> >> > > +        if ( old_cos > feat->ops.get_cos_max(feat) )
> >> >> > > +            old_cos = 0;
> >> >> > > +
> >> >> > > +        /* value getting order is same as feature array */
> >> >> > > +        feat->ops.get_old_val(val, feat, old_cos);
> >> >> > > +
> >> >> > > +        array_len -= feat->cos_num;
> >> >> > 
> >> >> > So this I should really have asked about on a much earlier patch,
> >> >> > but I've recognize the oddity only now: Why is cos_num
> >> >> > per-feature-node instead of per-feature? This should really be a
> >> >> > field in struct feat_ops (albeit the name "ops" then will be slightly
> >> >> > misleading, but I think that's tolerable if you can't think of a 
> >> >> > better
> >> >> > name).
> >> >> > 
> >> >> Ok, I got your meaning. How about 'feat_props'? No matter operations or
> >> >> variables are all properties of the feature.
> >> >> 
> >> > One more thing here. If we move 'cos_max' into 'feat_ops', we cannot 
> > declare
> >> > 'feat_ops' as const. Because we have to assign value to 'cos_max' in
> >> > cat_init_feature().
> >> 
> >> I don't see a problem with this. It's only the static variable which
> >> can't be const then anymore. The pointer used everywhere else
> >> easily can be, afaict.
> >> 
> > Because I want to assign the l3_cat_props to feat->props before executing
> > cat_init_feature(). The codes sequence is below. Then, in 
> > cat_init_feature(),
> > I can use 'feat' but not 'l3_cat_props' which is feature specific.
> > 
> > static void cat_init_feature(...)
> > {
> > ......
> >     feat->info.cbm_len = (regs->a & CAT_CBM_LEN_MASK) + 1;
> >     feat->props->cos_max = min(opt_cos_max, regs->d & CAT_COS_MAX_MASK);
> > ......
> > }
> > 
> > static struct feat_props l3_cat_props = {
> >     .cos_num = 1,
> > };
> > 
> > static void psr_cpu_init(void)
> > {
> > ......
> >         feat->props = &l3_cat_props;
> >         cat_init_feature(&regs, feat, info, PSR_SOCKET_L3_CAT);
> > ......
> > }
> 
> static void psr_cpu_init(void)
> {
> ......
>         cat_init_feature(&regs, &l3_cat_props, feat, info, PSR_SOCKET_L3_CAT);
>         feat->props = &l3_cat_props;
> ......
> }
> 
> > Then, back to the origin of this. I think feature-node is feature itself.
> > Everything in it is feature specific thing. Is it necessary to move values
> > into a sub-structure, 'feat_props'? If not doing this, we can keep
> > 'feat_ops' to only handle callback functions.
> 
> I'm not sure I understand what you're trying to tell me. I can only
> repeat what I've said before: The amount of feature specific
> callbacks should be reduced to the minimum necessary - the more
> generic code, the less code overall to maintain.
> 
My key point is: can we keep 'cos_num' and 'cos_max' into 'feat_node' but not
'feat_ops'? Because I think 'feat_node' represents a feature. It can keep
all feature specific things.

If you still think it is not good, can we define 'struct feat_props' without
const? Then, I can keep above code sequence.

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