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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Tue, 14 Sep 2021 21:11:14 -0700
Message-ID: <CAPcyv4hZZX4WscR41PUSXZhDLPR6LuXHNRcJDO52gb+3MahYAA@mail.gmail.com>
Subject: Re: [RESEND PATCH v4 1/4] drivers/nvdimm: Add nvdimm pmu structure
To:     kajoljain <kjain@linux.ibm.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Linux NVDIMM <nvdimm@lists.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Weiny, Ira" <ira.weiny@intel.com>,
        Vishal L Verma <vishal.l.verma@intel.com>,
        maddy@linux.ibm.com, Santosh Sivaraj <santosh@fossix.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Vaibhav Jain <vaibhav@linux.ibm.com>,
        atrajeev@linux.vnet.ibm.com, Thomas Gleixner <tglx@linutronix.de>,
        rnsastry@linux.ibm.com
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On Tue, Sep 14, 2021 at 9:08 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> 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.

That is to say...I think if another implementation followed it should
try to match as many common event names as papr_scm picked, and
possibly extend with its own rather than start with a papr_scm
specific namespace for everything.