Re: [RESEND PATCH v4 1/4] drivers/nvdimm: Add nvdimm pmu structure

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Sep 9, 2021 at 12:56 AM kajoljain <kjain@linux.ibm.com> wrote:
>
>
>
> On 9/8/21 3:29 AM, Dan Williams wrote:
> > Hi Kajol,
> >
> > Apologies for the delay in responding to this series, some comments below:
>
> Hi Dan,
>     No issues, thanks for reviewing the patches.
>
> >
> > On Thu, Sep 2, 2021 at 10:10 PM Kajol Jain <kjain@linux.ibm.com> wrote:
> >>
> >> A structure is added, called nvdimm_pmu, for performance
> >> stats reporting support of nvdimm devices. It can be used to add
> >> nvdimm pmu data such as supported events and pmu event functions
> >> like event_init/add/read/del with cpu hotplug support.
> >>
> >> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> >> Reviewed-by: Madhavan Srinivasan <maddy@linux.ibm.com>
> >> Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
> >> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
> >> ---
> >>  include/linux/nd.h | 43 +++++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 43 insertions(+)
> >>
> >> diff --git a/include/linux/nd.h b/include/linux/nd.h
> >> index ee9ad76afbba..712499cf7335 100644
> >> --- a/include/linux/nd.h
> >> +++ b/include/linux/nd.h
> >> @@ -8,6 +8,8 @@
> >>  #include <linux/ndctl.h>
> >>  #include <linux/device.h>
> >>  #include <linux/badblocks.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/perf_event.h>
> >>
> >>  enum nvdimm_event {
> >>         NVDIMM_REVALIDATE_POISON,
> >> @@ -23,6 +25,47 @@ enum nvdimm_claim_class {
> >>         NVDIMM_CCLASS_UNKNOWN,
> >>  };
> >>
> >> +/* Event attribute array index */
> >> +#define NVDIMM_PMU_FORMAT_ATTR         0
> >> +#define NVDIMM_PMU_EVENT_ATTR          1
> >> +#define NVDIMM_PMU_CPUMASK_ATTR                2
> >> +#define NVDIMM_PMU_NULL_ATTR           3
> >> +
> >> +/**
> >> + * struct nvdimm_pmu - data structure for nvdimm perf driver
> >> + *
> >> + * @name: name of the nvdimm pmu device.
> >> + * @pmu: pmu data structure for nvdimm performance stats.
> >> + * @dev: nvdimm device pointer.
> >> + * @functions(event_init/add/del/read): platform specific pmu functions.
> >
> > This is not valid kernel-doc:
> >
> > include/linux/nd.h:67: warning: Function parameter or member
> > 'event_init' not described in 'nvdimm_pmu'
> > include/linux/nd.h:67: warning: Function parameter or member 'add' not
> > described in 'nvdimm_pmu'
> > include/linux/nd.h:67: warning: Function parameter or member 'del' not
> > described in 'nvdimm_pmu'
> > include/linux/nd.h:67: warning: Function parameter or member 'read'
> > not described in 'nvdimm_pmu'
> >
> > ...but I think rather than fixing those up 'struct nvdimm_pmu' should be pruned.
> >
> > It's not clear to me that it is worth the effort to describe these
> > details to the nvdimm core which is just going to turn around and call
> > the pmu core. I'd just as soon have the driver call the pmu core
> > directly, optionally passing in attributes and callbacks that come
> > from the nvdimm core and/or the nvdimm provider.
>
> The intend for adding these callbacks(event_init/add/del/read) is to give
> flexibility to the nvdimm core to add some common checks/routines if required
> in the future. Those checks can be common for all architecture with still having the
> ability to call arch/platform specific driver code to use its own routines.
>
> But as you said, currently we don't have any common checks and it directly
> calling platform specific code, so we can get rid of it.
> Should we remove this part for now?

Yes, lets go direct to the perf api for now and await the need for a
common core wrapper to present itself.

>
>
> >
> > Otherwise it's also not clear which of these structure members are
> > used at runtime vs purely used as temporary storage to pass parameters
> > to the pmu core.
> >
> >> + * @attr_groups: data structure for events, formats and cpumask
> >> + * @cpu: designated cpu for counter access.
> >> + * @node: node for cpu hotplug notifier link.
> >> + * @cpuhp_state: state for cpu hotplug notification.
> >> + * @arch_cpumask: cpumask to get designated cpu for counter access.
> >> + */
> >> +struct nvdimm_pmu {
> >> +       const char *name;
> >> +       struct pmu pmu;
> >> +       struct device *dev;
> >> +       int (*event_init)(struct perf_event *event);
> >> +       int  (*add)(struct perf_event *event, int flags);
> >> +       void (*del)(struct perf_event *event, int flags);
> >> +       void (*read)(struct perf_event *event);
> >> +       /*
> >> +        * Attribute groups for the nvdimm pmu. Index 0 used for
> >> +        * format attribute, index 1 used for event attribute,
> >> +        * index 2 used for cpusmask attribute and index 3 kept as NULL.
> >> +        */
> >> +       const struct attribute_group *attr_groups[4];
> >
> > Following from above, I'd rather this was organized as static
> > attributes with an is_visible() helper for the groups for any dynamic
> > aspects. That mirrors the behavior of nvdimm_create() and allows for
> > device drivers to compose the attribute groups from a core set and /
> > or a provider specific set.
>
> Since we don't have any common events right now, Can I use papr
> attributes directly or should we create dummy events for common thing and
> then merged it with papr event list.

Just use papr events directly.