libcutils: add sched_policy test

Bug: 30597190

Change-Id: I51950e82235fa19bc92b3f7e8d190766d71af7df
Signed-off-by: Greg Hackmann <ghackmann@google.com>

libcutils/tests/Android.bp

@@ -21,6 +21,7 @@ cc_defaults {
             srcs: [
                 "MemsetTest.cpp",
                 "PropertiesTest.cpp",
+                "sched_policy_test.cpp",
                 "trace-dev_test.cpp",
             ],
         },

libcutils/tests/sched_policy_test.cpp

@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <algorithm>
+#include <chrono>
+#include <thread>
+#include <vector>
+
+#include <sys/capability.h>
+
+#include <cutils/sched_policy.h>
+
+#include <gtest/gtest.h>
+
+bool hasCapSysNice() {
+    __user_cap_header_struct header;
+    memset(&header, 0, sizeof(header));
+    header.version = _LINUX_CAPABILITY_VERSION_3;
+
+    __user_cap_data_struct caps[_LINUX_CAPABILITY_U32S_3];
+    if (capget(&header, &caps[0])) {
+        GTEST_LOG_(WARNING) << "failed to get process capabilities";
+        return false;
+    }
+
+    auto nice_idx = CAP_TO_INDEX(CAP_SYS_NICE);
+    auto nice_mask = CAP_TO_MASK(CAP_SYS_NICE);
+    return caps[nice_idx].effective & nice_mask;
+}
+
+long long medianSleepTime() {
+    std::vector<long long> sleepTimes;
+    constexpr size_t numSamples = 100;
+
+    for (size_t i = 0; i < numSamples; i++) {
+        auto start = std::chrono::steady_clock::now();
+        std::this_thread::sleep_for(std::chrono::nanoseconds(1));
+        auto end = std::chrono::steady_clock::now();
+
+        auto diff = end - start;
+        sleepTimes.push_back(diff.count());
+    }
+
+    constexpr auto median = numSamples / 2;
+    std::nth_element(sleepTimes.begin(), sleepTimes.begin() + median,
+            sleepTimes.end());
+    return sleepTimes[median];
+}
+
+TEST(SchedPolicy, set_sched_policy) {
+    if (!hasCapSysNice()) {
+        GTEST_LOG_(INFO) << "skipping test that requires CAP_SYS_NICE";
+        return;
+    }
+
+    // A measureable effect of scheduling policy is that the kernel has 800x
+    // greater slack time in waking up a sleeping background thread.
+    //
+    // Look for 100x difference in how long FB and BG threads actually sleep
+    // when trying to sleep for 1 ns.  This difference is large enough not
+    // to happen by chance, but small enough (compared to 800x) to keep inherent
+    // fuzziness in scheduler behavior from causing false negatives.
+    const unsigned int BG_FG_SLACK_FACTOR = 100;
+
+    ASSERT_EQ(0, set_sched_policy(0, SP_BACKGROUND));
+    auto bgSleepTime = medianSleepTime();
+
+    ASSERT_EQ(0, set_sched_policy(0, SP_FOREGROUND));
+    auto fgSleepTime = medianSleepTime();
+    ASSERT_GT(bgSleepTime, fgSleepTime * BG_FG_SLACK_FACTOR);
+}
+
+TEST(SchedPolicy, get_sched_policy) {
+    SchedPolicy policy;
+    ASSERT_EQ(0, get_sched_policy(0, &policy));
+
+    const char *policyName = get_sched_policy_name(policy);
+    EXPECT_NE(nullptr, policyName);
+    EXPECT_STRNE("error", policyName);
+
+    ASSERT_EQ(0, set_sched_policy(0, SP_BACKGROUND));
+    SchedPolicy newPolicy;
+    ASSERT_EQ(0, get_sched_policy(0, &newPolicy));
+    EXPECT_EQ(SP_BACKGROUND, newPolicy);
+}