Re: [Xen-devel] [PATCH v9 12/25] x86: refactor psr: L3 CAT: set value: implement cos id picking flow.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.03.17 at 14:10, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> On 17-03-30 05:55:52, Jan Beulich wrote:
>> >>> On 30.03.17 at 03:37, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>> > On 17-03-29 03:57:52, Jan Beulich wrote:
>> >> >>> On 29.03.17 at 03:36, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>> >> > On 17-03-29 09:20:21, Yi Sun wrote:
>> >> >> On 17-03-28 06:20:48, Jan Beulich wrote:
>> >> >> > >>> On 28.03.17 at 13:59, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>> >> >> > > I think we at least need a 'get_val()' hook.
>> >> >> > 
>> >> >> > Of course.
>> >> >> > 
>> >> >> > > I try to implement CAT/CDP hook.
>> >> >> > > Please help to check if this is what you thought.
>> >> >> > 
>> >> >> > One remark below, but other than that - yes.
>> >> >> > 
>> >> >> > > static void cat_get_val(const struct feat_node *feat, unsigned int 
>> >> >> > > cos,
>> >> >> > >                         enum cbm_type type, int flag, uint32_t 
>> >> >> > > *val)
>> >> >> > > {
>> >> >> > >     *val = feat->cos_reg_val[cos];
>> >> >> > > }
>> >> >> > > 
>> >> >> > > static void l3_cdp_get_val(const struct feat_node *feat, unsigned 
>> >> >> > > int 
>> > cos,
>> >> >> > >                            enum cbm_type type, int flag, uint32_t 
>> >> >> > > *val)
>> >> >> > > {
>> >> >> > >     if ( type == PSR_CBM_TYPE_L3_DATA || flag == 0 )
>> >> >> > >         *val = get_cdp_data(feat, cos);
>> >> >> > >     if ( type == PSR_CBM_TYPE_L3_CODE || flag == 1 )
>> >> >> > >         *val = get_cdp_code(feat, cos);
>> >> >> > > }
>> >> >> > 
>> >> >> > Why the redundancy between type and flag?
>> >> >> > 
>> >> >> For psr_get_val, upper layer input the cbm_type to get either DATA or 
>> >> >> CODE
>> >> >> value. For other cases, we use flag as cos_num index to get either 
>> >> >> DATA or
>> >> >> CODE.
>> >> >> 
>> >> > Let me explain more to avoid confusion. For other cases, we use cos_num 
>> >> > as
>> >> > index to get values from a feature. In these cases, we do not know the
>> >> > cbm_type of the feature. So, I use the cos_num as flag to make 'get_val'
>> >> > know which value should be returned.
>> >> 
>> >> I'm pretty sure this redundancy can be avoided.
>> >> 
>> > Then, I think I have to reuse the 'type'. As only CDP needs type to decide
>> > which value to be returned so far, I think I can implement codes like below
>> > to make CDP can handle all scenarios.
>> > 
>> > static void l3_cdp_get_val(const struct feat_node *feat, unsigned int cos,
>> >                            enum cbm_type type, uint32_t *val)
>> > {
>> >     if ( type == PSR_CBM_TYPE_L3_DATA || flag == 0xF000 )
>> >         *val = get_cdp_data(feat, cos);
>> >     if ( type == PSR_CBM_TYPE_L3_CODE || flag == 0xF001 )
>> >         *val = get_cdp_code(feat, cos);
>> > }
>> > 
>> > static bool fits_cos_max(...)
>> > {
>> > ......
>> >     for (i = 0; i < feat->props->cos_num; i++)
>> >     {
>> >         feat->props->get_val(feat, cos, i + 0xF000, &default_val);
>> >         if ( val[i] == default_val )
>> >             ......
>> >     }
>> > ......
>> > }
>> > 
>> > Is that good for you?
>> 
>> Urgh - no, not really: This is hackery. Do you have a tree
>> somewhere so I could look at the file after at least the CDP
>> patches have all been applied, to see whether I have a
>> better idea? Alternatively, could you attach psr.c the way
>> you have it right now with the entire series applied?
>> 
> I think you can check v9 codes here:
> https://github.com/yisun-git/xen/tree/l2_cat_v9 

Looking at this made me notice that cat_get_old_val() passes a
bogus literal 0 to cat_get_val(), which needs taking care of too.
One option I can see is for each feature to make available an
array of type enum cbm_type, with cos_num elements. The order
would match that of the order of values in their arrays. This will
allow elimination of all of the get_old_val, compare_val, and
fits_cos_max hooks afaict. At that point the "new" in
set_new_val is also no longer needed to contrast with the "old"
in the no longer existing get_old_val. Arguably insert_val may
be even slightly more precise in describing what the function
does.

The checks done first in what is currently *_set_new_val() also
look like they could be moved into the (generic) caller(s), making
clear that at least for now even cbm_len (just like suggested for
cos_max) should be a generic rather than unionized field in
struct feat_node. In the worst case a new check_val() hook
might be needed.

Jan

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