From 4afacef8c73dd1285140357cde15c5ccac1d483e Mon Sep 17 00:00:00 2001
From: duke <duke@openjdk.org>
Date: Mon, 23 Mar 2026 16:02:38 +0000
Subject: [PATCH] Backport 5c2ef74931c05cac1aa589a8e1f9c242361dc247

---
 .../jtreg/runtime/os/AvailableProcessors.java | 49 +++++++++++++++++--
 1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/test/hotspot/jtreg/runtime/os/AvailableProcessors.java b/test/hotspot/jtreg/runtime/os/AvailableProcessors.java
index 18201d99127..51d6742b832 100644
--- a/test/hotspot/jtreg/runtime/os/AvailableProcessors.java
+++ b/test/hotspot/jtreg/runtime/os/AvailableProcessors.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,6 +38,9 @@
 
 import java.util.ArrayList;
 import java.io.File;
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
 
 public class AvailableProcessors {
 
@@ -73,13 +76,17 @@ public static void main(String[] args) throws Exception {
                                                                      "AvailableProcessors");
 
             int[] expected = new int[] { 1, available/2, available-1, available };
+            int cpuId = getFirstAllowedCpu();
+            if (cpuId == -1) {
+                throw new SkippedException("Could not determine allowed CPU cores");
+            }
 
             for (int i : expected) {
                 System.out.println("Testing for " + i + " processors ...");
-                int max = i - 1;
+                int max = i - 1 + cpuId;
                 ArrayList<String> cmdline = new ArrayList<>(master.command());
                 // prepend taskset command
-                cmdline.add(0, "0-" + max);
+                cmdline.add(0, cpuId + "-" + max);
                 cmdline.add(0, "-c");
                 cmdline.add(0, taskset);
                 // append expected processor count
@@ -104,4 +111,40 @@ static void checkProcessors(int expected) {
         else
             System.out.println(SUCCESS_STRING + available);
     }
+
+    /**
+     * Retrieves the first available CPU core ID allowed for the current process on Linux.
+     *
+     * @return The first CPU ID in Cpus_allowed_list, or -1 if unavailable.
+     */
+    static int getFirstAllowedCpu() {
+        final String statusFile = "/proc/self/status";
+        final String targetKey = "Cpus_allowed_list:";
+
+        try (BufferedReader br = new BufferedReader(new FileReader(statusFile))) {
+            String line;
+            while ((line = br.readLine()) != null) {
+                // Look for the line starting with "Cpus_allowed_list:"
+                if (line.startsWith(targetKey)) {
+                    // Extract the value part, e.g., "0-15,32-47" or "80,82,84"
+                    String listValue = line.substring(targetKey.length()).trim();
+                    if (listValue.isEmpty()) return -1;
+
+                    // Get the first segment before any comma (e.g., "0-15" from "0-15,32")
+                    String firstSegment = listValue.split(",")[0];
+
+                    // If it is a range (e.g., "80-159"), take the start number
+                    if (firstSegment.contains("-")) {
+                        return Integer.parseInt(firstSegment.split("-")[0]);
+                    } else {
+                        // If it is a single ID (e.g., "1"), parse it directly
+                        return Integer.parseInt(firstSegment);
+                    }
+                }
+            }
+        } catch (IOException | NumberFormatException | ArrayIndexOutOfBoundsException e) {
+            throw new RuntimeException("Failed to read or parse " + statusFile, e);
+        }
+        return -1;
+    }
 }