libcutils: add sched_policy test

            srcs: [

                "MemsetTest.cpp",

                "PropertiesTest.cpp",

                "sched_policy_test.cpp",

                "trace-dev_test.cpp",

            ],

        },

/*

 * 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);

}