Re: [RFC PATCH v3 03/17] x86/resctrl: Detect Assignable Bandwidth Monitoring feature details

[Moger, Babu]

Hi Reinette,


On 5/10/2024 1:34 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 5/10/2024 10:01 AM, Moger, Babu wrote:
> > On 5/9/2024 10:18 PM, Reinette Chatre wrote:
> > > On 5/9/2024 3:34 PM, Moger, Babu wrote:
> > > > On 5/7/24 15:27, Reinette Chatre wrote:
> > > > > On 5/6/2024 12:09 PM, Moger, Babu wrote:
> > > > > > On 5/3/24 18:26, Reinette Chatre wrote:
> > > > > > > On 3/28/2024 6:06 PM, Babu Moger wrote:
> > > > >
> > > > > ...
> > > > >
> > > > > > > > + * @mbm_assign_cntrs:    Maximum number of assignable counters
> > > > > > > >     */
> > > > > > > >    struct rdt_resource {
> > > > > > > >        int            rid;
> > > > > > > > @@ -188,6 +198,8 @@ struct rdt_resource {
> > > > > > > >        struct list_head    evt_list;
> > > > > > > >        unsigned long        fflags;
> > > > > > > >        bool            cdp_capable;
> > > > > > > > +    bool            mbm_assign_capable;
> > > > > > > > +    u32                     mbm_assign_cntrs;
> > > > > > > >    };
> > > > > > >
> > > > > > > Please check tabs vs spaces (in this whole series please).
> > > > > >
> > > > > > Sure. Will do.
> > > > > >
> > > > > > > I'm thinking that a new "MBM specific" struct within
> > > > > > > struct rdt_resource will be helpful to clearly separate the MBM related
> > > > > > > data. This will be similar to struct resctrl_cache for
> > > > > > > cache allocation and struct resctrl_membw for memory bandwidth
> > > > > > > allocation.
> > > > > >
> > > > > > Did you mean to move all the fields for monitoring to move to new struct?
> > > > > >
> > > > > > Struct resctrl_mbm {
> > > > > >             int                     num_rmid;
> > > > > >             bool                    mbm_assign_capable;
> > > > > >             u32                     mbm_assign_cntrs;
> > > > > > }:
> > > > >
> > > > > Indeed, so not actually MBM specific but monitoring specific as you state (with
> > > > > appropriate naming?). This is purely to help organize data within struct rdt_resource
> > > > > and (similar to struct resctrl_cache and struct resctrl_membw) not a new
> > > > > structure expected to be passed around. I think evt_list can also be a member.
> > > >
> > > > How about this?
> > > >
> > > > Lets keep assign_capable in main structure(like we have mon_capable) and
> > > > move rest of them into new structure.
> > > >
> > > > Struct resctrl_mon {
> > > >              int                     num_rmid;
> > > >         struct list_head        evt_list;
> > > >              u32                     num_assign_cntrs;
> > > > }:
> > >
> > > This looks like a good start. It certainly supports ABMC. I do not yet
> > > have a clear understanding about how this will support MPAM and soft-RMID/ABMC
> > > since the current implementation has an implicit scope of one counter per event per
> > > monitor group. It thus seem reasonable to have a new generic name of "cntrs".
> >
> > How about renaming it to "assignable_counters"?
>
> As I mentioned in [1] the "assign" concept is not clear (just to me perhaps?). It
> really seems to be the marketing name percolating into the implementation. Why is
> "assignable" needed to be in a "counter" variable name? Is a variable not by definition
> "assignable"? Why not just, for example, "num_cntrs"? I believe that things to be
> as simple and obvious as possible ... this just helps to reduce confusion.

Ok. That sounds fine to me.
> My previous comment regarding counter scope is not addressed by a rename though and
> I do not expect you to have the answer but I would like us to keep in mind how these
> "counters" could end up getting used. We may just later, when soft-RMID/ABMC and MPAM
> is understood, need to add a "counter scope" as well.

Sure.

> Reinette
>
> [1] https://lore.kernel.org/lkml/0d94849c-828c-4f10-a6f8-e26cc4554909@xxxxxxxxx/

Thanks
- Babu Moger