From e1a4049b11a403d925778538093fb4b8720eba0b Mon Sep 17 00:00:00 2001
From: Victor Kuznetsov <vikuznetsov@nvidia.com>
Date: Wed, 22 Jul 2026 23:31:30 +0400
Subject: [PATCH] [infra] Reduce default build parallelism

Leave CPU, power, and SMT headroom while retaining the Docker build's memory cap.
---
 build_release.sh                   |  5 +++--
 scripts/build_cuvslam_in_docker.sh | 11 ++++++-----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/build_release.sh b/build_release.sh
index bd98f8d..cd5fa69 100755
--- a/build_release.sh
+++ b/build_release.sh
@@ -15,7 +15,7 @@
 #   --build_docs       Build documentation
 #   --build_type=TYPE  Set CMake build type (Debug|Release[default]|RelWithDebInfo|MinSizeRel)
 #   --cuda_arch=ARCH   Set CUDA architecture target (e.g. 87 for Orin Nano, default: all)
-#   --jobs=N           Set number of parallel jobs (default: 8)
+#   --jobs=N           Set parallel jobs (default: ceil(nproc/2))
 #
 # Environment variables (optional):
 #   CUVSLAM_SRC_DIR      Source directory (default: /cuvslam/src)
@@ -46,7 +46,8 @@ USE_RERUN=OFF
 SRC=/cuvslam/src
 DST=/cuvslam/build
 
-MAKE_JOBS=$(nproc 2>/dev/null || echo 8)
+nproc_n=$(nproc 2>/dev/null || echo 8)
+MAKE_JOBS=$(( (nproc_n + 1) / 2 ))
 
 if [ ${CUVSLAM_SRC_DIR+x} ]; then
   echo "Using environment variable CUVSLAM_SRC_DIR='$CUVSLAM_SRC_DIR'."
diff --git a/scripts/build_cuvslam_in_docker.sh b/scripts/build_cuvslam_in_docker.sh
index 7586bf9..90ffffe 100755
--- a/scripts/build_cuvslam_in_docker.sh
+++ b/scripts/build_cuvslam_in_docker.sh
@@ -12,7 +12,7 @@ if [ "$#" -lt 1 ] || [ "$#" -gt 2 ]; then
   echo "  EXTRA_CMAKE_ARGS  Additional CMake arguments"
   echo "  CUVSLAM_REQUIRE_CLEAN_SOURCE  Fail if tracked source files differ from HEAD"
   echo "  BUILD_JOBS      Parallel build jobs, passed as --jobs to build_release.sh"
-  echo "                  (default: min(nproc, MemAvailable/4GB) to avoid OOM)"
+  echo "                  (default: min(ceil(nproc/2), MemAvailable/4GB))"
   exit 1
 fi
 
@@ -37,19 +37,20 @@ DOCKER_USER="--user $(id -u):$(id -g) --group-add video -e HOME=/tmp"
 TTY_FLAG=""
 [ -t 0 ] && TTY_FLAG="-it"
 
-# Cap parallelism so each compile job has ~4GB of available memory, avoiding OOM
-# on memory-constrained runners (e.g. Jetson Thor). Override by setting BUILD_JOBS.
+# Cap parallelism at half the available CPUs to leave power and SMT headroom,
+# and at ~4GB of available memory per compile job. Override by setting BUILD_JOBS.
 if [ -z "${BUILD_JOBS:-}" ]; then
   nproc_n=$(nproc)
+  cpu_cap=$(( (nproc_n + 1) / 2 ))
   mem_cap=$(awk '/MemAvailable/ { print int($2/1024/1024/4) }' /proc/meminfo)
   if [ "$mem_cap" -lt 1 ]; then
     mem_cap=1
   fi
-  BUILD_JOBS=$nproc_n
+  BUILD_JOBS=$cpu_cap
   if [ "$mem_cap" -lt "$BUILD_JOBS" ]; then
     BUILD_JOBS=$mem_cap
   fi
-  echo "Build parallelism: --jobs=$BUILD_JOBS (nproc=$nproc_n, mem-capped jobs=${mem_cap} at 4GB/job)"
+  echo "Build parallelism: --jobs=$BUILD_JOBS (nproc=$nproc_n, CPU cap=$cpu_cap, memory cap=$mem_cap at 4GB/job)"
 fi
 
 JOBS_ARG=()