amari.{kpi,drb}: Fix multicell handling

1) Fix amari.kpi to handle stats messages in enb.xlog that come with multiple cells.
   Previously such messages were leading to the following errors on KPI calculator place (e.g. Wendelin):

        xlte.amari.kpi.LogError: t1731059787.321: stats describes 2 cells;  but only single-cell configurations are supported

2) Fix amari.drb to generate x.drb_stats messages when an UE is associated to multiple cells due to e.g. Carrier Aggregation.
   Previously CA was leading to

        raise RuntimeError(("ue #%s belongs to %d cells;  "+
            "but only single-cell configurations are supported") % (ue_id, len(ju(['cells']))))

   error on eNB side.

+ minor fixes and enhancements done along the way.

Please see individual patches for details.

An example enb.xlog for eNB with 2 cells and an UE Carrier-Aggregated to both cells is here:

https://lab.nexedi.com/kirr/misc/-/blob/6a04cf3/lte/20241111-2cell.xlog

And here is how it looks when visualized via kpidemo.py :

https://lab.nexedi.com/kirr/misc/-/blob/6a04cf3/lte/20241111-2cell.png

Kirill

/cc @lu.xu
/reviewed-by @paul.graydon
/reviewed-on kirr/xlte!7

amari/kpi.py

 # -*- coding: utf-8 -*-
-# Copyright (C) 2022-2023  Nexedi SA and Contributors.
+# Copyright (C) 2022-2024  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -225,11 +225,12 @@ def _handle_stats(logm, stats: xlog.Message, m_prev: kpi.Measurement):
     #   preserve statistical properties, but not more. See m_initfini below for
     #   details.
     #
-    # - it is possible to handle eNB with single cell only. This limitation
+    # - it is not easy to produce per-cell measurements. This limitation
     #   comes from the fact that in Amarisoft LTE stack S1-related counters
     #   come as "globals" ones, while e.g. RRC-related counters are "per-cell".
-    #   It is thus not possible to see how much S1 connection establishments
-    #   are associated with one particular cell if there are several of them.
+    #   It is thus hard to see how much S1 connection establishments are associated
+    #   with one particular cell if there are several of them. One S1 connection could
+    #   be even related to multiple cells simultaneously when carriers are aggregated.
     #
     # TODO also parse enb.log to fix those issues.
 
@@ -259,7 +260,7 @@ def _handle_stats(logm, stats: xlog.Message, m_prev: kpi.Measurement):
     # do init/fini correction if there was also third preceding stats message.
     m = logm._m.copy() # [stats_prev, stats)
 
-    # δcc(counter) tells how specified cumulative counter changed since last stats result.
+    # δcc(counter) tells how specified global cumulative counter changed since last stats result.
     def δcc(counter):
         old = _stats_cc(stats_prev, counter)
         new = _stats_cc(stats,      counter)
@@ -267,6 +268,14 @@ def _handle_stats(logm, stats: xlog.Message, m_prev: kpi.Measurement):
             raise LogError(stats.timestamp, "cc %s↓  (%s → %s)" % (counter, old, new))
         return new - old
 
+    # δcell_cc(counter) tells how specified per-cell cumulative counter changed since last stats result.
+    def δcell_cc(cell, counter):
+        old = _stats_cell_cc(stats_prev, cell, counter)
+        new = _stats_cell_cc(stats,      cell, counter)
+        if new < old:
+            raise LogError(stats.timestamp, "cc C%s.%s↓  (%s → %s)" % (cell, counter, old, new))
+        return new - old
+
     # m_initfini populates m[init] and m[fini] from vinit and vfini values.
     # copy of previous ._m[fini] is correspondingly adjusted for init/fini correction.
     p = None
@@ -297,9 +306,24 @@ def _handle_stats(logm, stats: xlog.Message, m_prev: kpi.Measurement):
     # any logic error in data will be reported via LogError.
     try:
         # RRC: connection establishment
+        #
+        # Aggregate statistics for all cells because in E-RAB Accessibility we need
+        # aggregated RRC.ConnEstab* for whole eNB. It would be more logical to emit
+        # per-cell RRC statistics here and aggregate the result in KPI computation
+        # routine, but for now we are not delving to rework kpi.Measurement to
+        # contain per-cell values. For E-RAB Accessibility the end result is the
+        # same whether we do aggregation here or in kpi.Calc.erab_accessibility().
+        #
+        # TODO rework to emit per-cell measurements when/if we need per-cell KPIs
+        cells = set(stats['cells'].keys())  # NOTE cells are taken only from stats, not from stat_prev
+        δΣcell_rrc_connection_request = 0   # (if a cell disappears its counters stop to be accounted)
+        δΣcell_rrc_connection_setup_complete = 0
+        for cell in cells:
+            δΣcell_rrc_connection_request         += δcell_cc(cell, 'rrc_connection_request')
+            δΣcell_rrc_connection_setup_complete  += δcell_cc(cell, 'rrc_connection_setup_complete')
         m_initfini(
-            'RRC.ConnEstabAtt.sum',         δcc('rrc_connection_request'),
-            'RRC.ConnEstabSucc.sum',        δcc('rrc_connection_setup_complete'))
+            'RRC.ConnEstabAtt.sum',         δΣcell_rrc_connection_request,
+            'RRC.ConnEstabSucc.sum',        δΣcell_rrc_connection_setup_complete)
 
         # S1: connection establishment
         m_initfini(
@@ -334,37 +358,28 @@ def _handle_stats(logm, stats: xlog.Message, m_prev: kpi.Measurement):
 
 
 # _stats_check verifies stats message to have required structure.
-#
-# only configurations with one single cell are supported.
-# ( because else it would not be clear to which cell to associate e.g. global
-#   counters for S1 messages )
 def _stats_check(stats: xlog.Message):
-    cells = stats['cells']
-    if len(cells) != 1:
-        raise LogError(stats.timestamp, "stats describes %d cells;  but only single-cell configurations are supported" % len(cells))
-    cellname = list(cells.keys())[0]
-
     try:
         stats.get1("counters", dict).get1("messages", dict)
-        stats.get1("cells", dict).get1(cellname, dict).get1("counters", dict).get1("messages", dict)
+        cells = stats.get1("cells", dict)
+        for cell in cells:
+            cells.get1(cell, dict).get1("counters", dict).get1("messages", dict)
     except Exception as e:
         raise LogError(stats.timestamp, "stats: %s" % e)  from None
     return
 
-# _stats_cc returns specified cumulative counter from stats result.
+# _stats_cc returns specified global cumulative counter from stats result.
 #
-# counter may be both "global" or "per-cell".
 # stats is assumed to be already verified by _stats_check.
 def _stats_cc(stats: xlog.Message, counter: str):
-    cells = stats['cells']
-    cell = list(cells.values())[0]
-
-    if counter.startswith("rrc_"):
-        cc_dict = cell ['counters']
-    else:
-        cc_dict = stats['counters']
+    return stats['counters']['messages'].get(counter, 0)
 
-    return cc_dict['messages'].get(counter, 0)
+# _stats_cell_cc is like _stats_cc but returns specified per-cell cumulative counter from stats result.
+def _stats_cell_cc(stats: xlog.Message, cell: str, counter: str):
+    _ = stats['cells'].get(cell)
+    if _ is None:
+        return 0    # cell is absent in this stats
+    return _['counters']['messages'].get(counter, 0)
 
 
 # _handle_drb_stats handles next x.drb_stats xlog entry upon _read request.
@@ -465,9 +480,9 @@ def _drb_update(m: kpi.Measurement, drb_stats: xlog.Message):
             ΣT_hi   = ΣT + ΣT_err
             ΣTT_lo  = ΣTT - ΣTT_err
 
-            qvol[qci]      = 8*ΣB   # in bits
-            qtime[qci]     = (ΣT_hi + ΣTT_lo) / 2
-            qtime_err[qci] = (ΣT_hi - ΣTT_lo) / 2
+            qvol[qci]      += 8*ΣB   # in bits
+            qtime[qci]     += (ΣT_hi + ΣTT_lo) / 2
+            qtime_err[qci] += (ΣT_hi - ΣTT_lo) / 2
 
 
 # LogError(timestamp|None, *argv).

kpi.py

 # -*- coding: utf-8 -*-
-# Copyright (C) 2022-2023  Nexedi SA and Contributors.
+# Copyright (C) 2022-2024  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -655,8 +655,6 @@ def eutran_ip_throughput(calc): # -> IPThp[QCI][dl,ul]
     qulΣte = np.zeros(nqci, dtype=np.float64)
 
     for m in calc._miter():
-        τ = m['X.δT']
-
         for qci in range(nqci):
             dl_vol      = m["DRB.IPVolDl.QCI"]          [qci]
             dl_time     = m["DRB.IPTimeDl.QCI"]         [qci]