runInLinuxVM: apply Qemu's vCPU limit (#386224)

2025-03-04 06:12:25 -08:00
parent ee2c1b8352 64503c8633
commit 242b16a7dd
1 changed files with 8 additions and 2 deletions
@@ -247,11 +247,17 @@ rec {
    eval "$preVM"

    if [ "$enableParallelBuilding" = 1 ]; then
+      QEMU_NR_VCPUS=0
      if [ ''${NIX_BUILD_CORES:-0} = 0 ]; then
-        QEMU_OPTS+=" -smp cpus=$(nproc)"
+        QEMU_NR_VCPUS="$(nproc)"
      else
-        QEMU_OPTS+=" -smp cpus=$NIX_BUILD_CORES"
+        QEMU_NR_VCPUS="$NIX_BUILD_CORES"
      fi
+      # qemu only supports 255 vCPUs (see error from `qemu-system-x86_64 -smp 256`)
+      if [ "$QEMU_NR_VCPUS" -gt 255 ]; then
+        QEMU_NR_VCPUS=255
+      fi
+      QEMU_OPTS+=" -smp cpus=$QEMU_NR_VCPUS"
    fi

    # Write the command to start the VM to a file so that the user can