[RFC PATCH 0/4] powerpc/papr_scm: Add support for reporting NVDIMM performance statistics

[Vaibhav Jain <vaibhav@linux.ibm.com>]

The patch-set proposes to add support for fetching and reporting
performance statistics for PAPR compliant NVDIMMs as described in
documentation for H_SCM_PERFORMANCE_STATS hcall Ref[1]. The patch-set
also implements mechanisms to expose NVDIMM performance stats via
sysfs and newly introduced PDSMs[2] for libndctl.

This patch-set combined with corresponding ndctl and libndctl changes
proposed at Ref[3] should enable user to fetch PAPR compliant NVDIMMs
using following command:

 # ndctl list -D --stats
[
  {
    "dev":"nmem0",
    "stats":{
      "Controller Reset Count":2,
      "Controller Reset Elapsed Time":603331,
      "Power-on Seconds":603931,
      "Life Remaining":"100%",
      "Critical Resource Utilization":"0%",
      "Host Load Count":5781028,
      "Host Store Count":8966800,
      "Host Load Duration":975895365,
      "Host Store Duration":716230690,
      "Media Read Count":0,
      "Media Write Count":6313,
      "Media Read Duration":0,
      "Media Write Duration":9679615,
      "Cache Read Hit Count":5781028,
      "Cache Write Hit Count":8442479,
      "Fast Write Count":8969912
    }
  }
]

The patchset is dependent on existing patch-set "[PATCH v7 0/5]
powerpc/papr_scm: Add support for reporting nvdimm health" available
at Ref[2] that adds support for reporting PAPR compliant NVDIMMs in
'papr_scm' kernel module.

Structure of the patch-set
==========================

The patch-set starts with implementing functionality in papr_scm
module to issue H_SCM_PERFORMANCE_STATS hcall, fetch & parse dimm
performance stats and exposing them as a PAPR specific libnvdimm
attribute named 'perf_stats'

Patch-2 introduces a new PDSM named FETCH_PERF_STATS that can be
issued by libndctl asking papr_scm to issue the
H_SCM_PERFORMANCE_STATS hcall using helpers introduced earlier and
storing the results in a dimm specific perf-stats-buffer.

Patch-3 introduces a new PDSM named READ_PERF_STATS that can be
issued by libndctl to read the perf-stats-buffer in an incremental
manner to workaround the 256-bytes envelop limitation of libnvdimm.

Finally Patch-4 introduces a new PDSM named GET_PERF_STAT that can be
issued by libndctl to read values of a specific NVDIMM performance
stat like "Life Remaining".

References
==========
[1] Documentation/powerpc/papr_hcals.rst

[2] https://lore.kernel.org/linux-nvdimm/20200508104922.72565-1-vaibhav@linux.ibm.com/

[3] https://github.com/vaibhav92/ndctl/tree/papr_scm_stats_v1

Vaibhav Jain (4):
  powerpc/papr_scm: Fetch nvdimm performance stats from PHYP
  powerpc/papr_scm: Add support for PAPR_SCM_PDSM_FETCH_PERF_STATS
  powerpc/papr_scm: Implement support for PAPR_SCM_PDSM_READ_PERF_STATS
  powerpc/papr_scm: Add support for PDSM GET_PERF_STAT

 Documentation/ABI/testing/sysfs-bus-papr-scm  |  27 ++
 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h |  60 +++
 arch/powerpc/platforms/pseries/papr_scm.c     | 391 ++++++++++++++++++
 3 files changed, 478 insertions(+)

-- 
2.26.2
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