scripts/trace: use ijson to parse the traces

Since the trace files can get very large (several GBs), parsing them
using python's json module might require an unfeasible amount of memory,
as it needs to load the whole file first.  The ijson [1] library
provides interfaces for parsing files iteratively, only loading a small
portion of a file at a time.

It requires the input JSON to have the tsc_rate and the definitions of
the tracepoints listed before the tracepoint entries.  It's not a big
deal, as this is the way `spdk_trace` generates it, but it's worth
noting, as passing that file through something like `jq -S` might make
it unreadable to the trace script.

[1] https://pypi.org/project/ijson

Signed-off-by: Konrad Sztyber <konrad.sztyber@intel.com>
Change-Id: I03c0c3fb47091da615a3978b8d63edf4d876b811
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/8275
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Mellanox Build Bot
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Monica Kenguva <monica.kenguva@intel.com>

scripts/bpf/trace.py

@@ -4,7 +4,7 @@ from argparse import ArgumentParser
 from dataclasses import dataclass, field
 from itertools import islice
 from typing import Dict, List, TypeVar
-import json
+import ijson
 import os
 import re
 import subprocess
@@ -168,21 +168,40 @@ class TraceEntry:
 class Trace:
     """Stores, parses, and prints out SPDK traces"""
     def __init__(self, file):
-        self._json = json.load(file)
+        self._parser = ijson.parse(file)
         self._objects = []
         self._argfmt = {TracepointArgument.TYPE_PTR: lambda a: f'0x{a:x}'}
-        self.tpoints = {t.id: t for t in self._parse_tpoints()}
-        self.tsc_rate = self._json['tsc_rate']
+        self.tpoints = {}
+        self._parse_defs()
 
-    def _parse_tpoints(self):
-        for tpoint in self._json.get('tpoints', []):
-            yield Tracepoint(
-                name=tpoint['name'], id=tpoint['id'],
+    def _parse_tpoints(self, tpoints):
+        for tpoint in tpoints:
+            tpoint_id = tpoint['id']
+            self.tpoints[tpoint_id] = Tracepoint(
+                name=tpoint['name'], id=tpoint_id,
                 new_object=tpoint['new_object'],
                 args=[TracepointArgument(name=a['name'],
                                          argtype=a['type'])
                       for a in tpoint.get('args', [])])
 
+    def _parse_defs(self):
+        builder = None
+        for prefix, event, value in self._parser:
+            # If we reach entries array, there are no more tracepoint definitions
+            if prefix == 'entries':
+                break
+            elif prefix == 'tsc_rate':
+                self.tsc_rate = value
+                continue
+
+            if (prefix, event) == ('tpoints', 'start_array'):
+                builder = ijson.ObjectBuilder()
+            if builder is not None:
+                builder.event(event, value)
+            if (prefix, event) == ('tpoints', 'end_array'):
+                self._parse_tpoints(builder.value)
+                builder = None
+
     def _parse_entry(self, entry):
         tpoint = self.tpoints[entry['tpoint']]
         obj = entry.get('object', {})
@@ -193,8 +212,15 @@ class Trace:
                           args={n.name: v for n, v in zip(tpoint.args, entry.get('args', []))})
 
     def _entries(self):
-        for entry in self._json.get('entries', []):
-            yield self._parse_entry(entry)
+        builder = None
+        for prefix, event, value in self._parser:
+            if (prefix, event) == ('entries.item', 'start_map'):
+                builder = ijson.ObjectBuilder()
+            if builder is not None:
+                builder.event(event, value)
+            if (prefix, event) == ('entries.item', 'end_map'):
+                yield self._parse_entry(builder.value)
+                builder = None
 
     def _annotate_args(self, entry):
         annotations = {}

scripts/pkgdep/arch.sh

@@ -7,6 +7,7 @@ pacman -Sy --needed --noconfirm gcc make cmake cunit libaio openssl \
 pacman -Sy --needed --noconfirm python-pexpect python-pip libffi
 pip install configshell_fb
 pip install pyelftools
+pip install ijson
 # Additional dependencies for DPDK
 pacman -Sy --needed --noconfirm numactl nasm
 # Additional dependencies for ISA-L used in compression

scripts/pkgdep/debian.sh

@@ -13,6 +13,7 @@ if ! pip3 install meson; then
 	apt-get install -y meson
 fi
 pip3 install pyelftools
+pip3 install ijson
 # Additional dependencies for SPDK CLI - not available on older Ubuntus
 apt-get install -y python3-configshell-fb python3-pexpect || echo \
 	"Note: Some SPDK CLI dependencies could not be installed."

scripts/pkgdep/rhel.sh

@@ -95,6 +95,7 @@ yum install -y python3-pip
 pip3 install ninja
 pip3 install meson
 pip3 install pyelftools
+pip3 install ijson
 
 # Additional dependencies for SPDK CLI - not available in rhel and centos
 if ! echo "$ID $VERSION_ID" | grep -E -q 'rhel 7|centos 7'; then