From f0ad37e3cd87e8ff3f8758e2fcd1f35de0cb6fe8 Mon Sep 17 00:00:00 2001
From: Takashi Kajinami <kajinamit@oss.nttdata.com>
Date: Mon, 8 Sep 2025 20:56:58 +0900
Subject: [PATCH] Lower down max_threads

Currently max_threads defaults to 5 * (number of CPU cores). Because
ThreadPool is created in each worker, and max_workers defaults to
(number of CPU cores), the total number of threads is by default
5 * (number of CPU cores) * (number of CPU cores) . In case a node has
24 cores CPU, orchestrator may launch 2880 threads at maximum, which is
too large. (Note that it may even launch doubled number of threads due
to separate workers for rating processing and reprocessing).

Lower down the default max_threads, by getting rid of the factor
dependent on number of CPU cores, to have reasonable cap by default.

Change-Id: I0efbf6b9e5331acc0d9f334cbbe6bebeecc5722a
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
---
 cloudkitty/orchestrator.py                                | 8 +++-----
 .../notes/lower-down-max-threads-be7e9fdf8dd45343.yaml    | 5 +++++
 2 files changed, 8 insertions(+), 5 deletions(-)
 create mode 100644 releasenotes/notes/lower-down-max-threads-be7e9fdf8dd45343.yaml

diff --git a/cloudkitty/orchestrator.py b/cloudkitty/orchestrator.py
index c89fe707..38e1e482 100644
--- a/cloudkitty/orchestrator.py
+++ b/cloudkitty/orchestrator.py
@@ -64,18 +64,16 @@ orchestrator_opts = [
     cfg.IntOpt(
         'max_workers_reprocessing',
         default=multiprocessing.cpu_count(),
+        sample_default=4,
         min=0,
         help='Max number of workers to execute the reprocessing. Defaults to '
              'the number of available CPU cores.'),
     cfg.IntOpt('max_threads',
-               # NOTE(peschk_l): This is the futurist default
-               default=multiprocessing.cpu_count() * 5,
-               sample_default=20,
+               default=16,
                min=1,
                deprecated_name='max_greenthreads',
                advanced=True,
-               help='Maximal number of threads to use per worker. Defaults to '
-               '5 times the number of available CPUs'),
+               help='Maximal number of threads to use per worker.')
 ]
 
 CONF.register_opts(orchestrator_opts, group='orchestrator')
diff --git a/releasenotes/notes/lower-down-max-threads-be7e9fdf8dd45343.yaml b/releasenotes/notes/lower-down-max-threads-be7e9fdf8dd45343.yaml
new file mode 100644
index 00000000..d07b2108
--- /dev/null
+++ b/releasenotes/notes/lower-down-max-threads-be7e9fdf8dd45343.yaml
@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    The ``[orchestrator] max_threads`` parameter now defaults to 16, to avoid
+    too many threads in total in node with many CPU cores.