Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 703 insertions, 0 deletions

diff --git a/src/seastar/apps/io_tester/CMakeLists.txt b/src/seastar/apps/io_tester/CMakeLists.txt
new file mode 100644
index 000000000..266ff4e54
--- /dev/null
+++ b/src/seastar/apps/io_tester/CMakeLists.txt
@@ -0,0 +1,27 @@
+#
+# This file is open source software, licensed to you under the terms
+# of the Apache License, Version 2.0 (the "License").  See the NOTICE file
+# distributed with this work for additional information regarding copyright
+# ownership.  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.
+#
+
+#
+# Copyright (C) 2018 Scylladb, Ltd.
+#
+
+seastar_add_app (io_tester
+  SOURCES io_tester.cc)
+
+target_link_libraries (app_io_tester
+  PRIVATE yaml-cpp::yaml-cpp)
diff --git a/src/seastar/apps/io_tester/conf.yaml b/src/seastar/apps/io_tester/conf.yaml
new file mode 100644
index 000000000..e8b8091c2
--- /dev/null
+++ b/src/seastar/apps/io_tester/conf.yaml
@@ -0,0 +1,25 @@
+- name: big_writes
+  shards: all
+  type: seqwrite
+  shard_info:
+    parallelism: 10
+    reqsize: 256kB
+    shares: 10
+    think_time: 0
+
+- name: latency_reads
+  shards: [0]
+  type: randread
+  shard_info:
+    parallelism: 1
+    reqsize: 512
+    shares: 100
+    think_time: 1000us
+
+- name: cpu_hog
+  shards: [0]
+  type: cpu
+  shard_info:
+    parallelim: 1
+    execution_time: 90us
+    think_time: 10us
diff --git a/src/seastar/apps/io_tester/io_tester.cc b/src/seastar/apps/io_tester/io_tester.cc
new file mode 100644
index 000000000..f6229b111
--- /dev/null
+++ b/src/seastar/apps/io_tester/io_tester.cc
@@ -0,0 +1,651 @@
+/*
+ * This file is open source software, licensed to you under the terms
+ * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
+ * distributed with this work for additional information regarding copyright
+ * ownership.  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.
+ */
+/*
+ * Copyright (C) 2017 ScyllaDB
+ */
+#include <seastar/core/app-template.hh>
+#include <seastar/core/distributed.hh>
+#include <seastar/core/reactor.hh>
+#include <seastar/core/future.hh>
+#include <seastar/core/shared_ptr.hh>
+#include <seastar/core/file.hh>
+#include <seastar/core/sleep.hh>
+#include <seastar/core/align.hh>
+#include <seastar/core/timer.hh>
+#include <seastar/core/thread.hh>
+#include <seastar/core/print.hh>
+#include <seastar/core/loop.hh>
+#include <seastar/core/with_scheduling_group.hh>
+#include <chrono>
+#include <vector>
+#include <boost/range/irange.hpp>
+#include <boost/algorithm/string.hpp>
+#include <boost/accumulators/accumulators.hpp>
+#include <boost/accumulators/statistics/stats.hpp>
+#include <boost/accumulators/statistics/max.hpp>
+#include <boost/accumulators/statistics/mean.hpp>
+#include <boost/accumulators/statistics/p_square_quantile.hpp>
+#include <boost/accumulators/statistics/extended_p_square.hpp>
+#include <boost/accumulators/statistics/extended_p_square_quantile.hpp>
+#include <boost/range/adaptor/filtered.hpp>
+#include <boost/range/adaptor/map.hpp>
+#include <boost/array.hpp>
+#include <iomanip>
+#include <random>
+#include <yaml-cpp/yaml.h>
+
+using namespace seastar;
+using namespace std::chrono_literals;
+using namespace boost::accumulators;
+
+static auto random_seed = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
+static std::default_random_engine random_generator(random_seed);
+// size of each individual file. Every class will have its file, so in a normal system with many shards, we'll naturally have many files and
+// that will push the data out of the disk's cache. And static sizes per file are simpler.
+static constexpr uint64_t file_data_size = 1ull << 30;
+
+class context;
+enum class request_type { seqread, seqwrite, randread, randwrite, append, cpu };
+
+namespace std {
+
+template <>
+struct hash<request_type> {
+    size_t operator() (const request_type& type) const {
+        return static_cast<size_t>(type);
+    }
+};
+
+}
+
+struct byte_size {
+    uint64_t size;
+};
+
+struct duration_time {
+    std::chrono::duration<float> time;
+};
+
+class shard_config {
+    std::unordered_set<unsigned> _shards;
+public:
+    shard_config()
+        : _shards(boost::copy_range<std::unordered_set<unsigned>>(boost::irange(0u, smp::count))) {}
+    shard_config(std::unordered_set<unsigned> s) : _shards(std::move(s)) {}
+
+    bool is_set(unsigned cpu) const {
+        return _shards.count(cpu);
+    }
+};
+
+struct shard_info {
+    unsigned parallelism = 10;
+    unsigned shares = 10;
+    uint64_t request_size = 4 << 10;
+    std::chrono::duration<float> think_time = 0ms;
+    std::chrono::duration<float> execution_time = 1ms;
+    seastar::scheduling_group scheduling_group = seastar::default_scheduling_group();
+};
+
+struct options {
+    bool dsync = false;
+};
+
+class class_data;
+
+struct job_config {
+    std::string name;
+    request_type type;
+    shard_config shard_placement;
+    ::shard_info shard_info;
+    ::options options;
+    std::unique_ptr<class_data> gen_class_data();
+};
+
+std::array<double, 4> quantiles = { 0.5, 0.95, 0.99, 0.999};
+
+class class_data {
+protected:
+    using accumulator_type = accumulator_set<double, stats<tag::extended_p_square_quantile(quadratic), tag::mean, tag::max>>;
+
+    job_config _config;
+    uint64_t _alignment;
+    uint64_t _last_pos = 0;
+
+    io_priority_class _iop;
+    seastar::scheduling_group _sg;
+
+    size_t _data = 0;
+    std::chrono::duration<float> _total_duration;
+
+    std::chrono::steady_clock::time_point _start = {};
+    accumulator_type _latencies;
+    std::uniform_int_distribution<uint32_t> _pos_distribution;
+    file _file;
+
+    virtual future<> do_start(sstring dir) = 0;
+    virtual future<size_t> issue_request(char *buf) = 0;
+public:
+    static int idgen();
+    class_data(job_config cfg)
+        : _config(std::move(cfg))
+        , _alignment(_config.shard_info.request_size >= 4096 ? 4096 : 512)
+        , _iop(engine().register_one_priority_class(format("test-class-{:d}", idgen()), _config.shard_info.shares))
+        , _sg(cfg.shard_info.scheduling_group)
+        , _latencies(extended_p_square_probabilities = quantiles)
+        , _pos_distribution(0,  file_data_size / _config.shard_info.request_size)
+    {}
+
+    virtual ~class_data() = default;
+
+    future<> issue_requests(std::chrono::steady_clock::time_point stop) {
+        _start = std::chrono::steady_clock::now();
+        return with_scheduling_group(_sg, [this, stop] {
+            return parallel_for_each(boost::irange(0u, parallelism()), [this, stop] (auto dummy) mutable {
+                auto bufptr = allocate_aligned_buffer<char>(this->req_size(), _alignment);
+                auto buf = bufptr.get();
+                return do_until([stop] { return std::chrono::steady_clock::now() > stop; }, [this, buf, stop] () mutable {
+                    auto start = std::chrono::steady_clock::now();
+                    return issue_request(buf).then([this, start, stop] (auto size) {
+                        auto now = std::chrono::steady_clock::now();
+                        if (now < stop) {
+                            this->add_result(size, std::chrono::duration_cast<std::chrono::microseconds>(now - start));
+                        }
+                        return think();
+                    });
+                }).finally([bufptr = std::move(bufptr)] {});
+            });
+        }).then([this] {
+            _total_duration = std::chrono::steady_clock::now() - _start;
+        });
+    }
+
+    future<> think() {
+        if (_config.shard_info.think_time > 0us) {
+            return seastar::sleep(std::chrono::duration_cast<std::chrono::microseconds>(_config.shard_info.think_time));
+        } else {
+            return make_ready_future<>();
+        }
+    }
+    // Generate the test file for reads and writes alike. It is much simpler to just generate one file per job instead of expecting
+    // job dependencies between creators and consumers. So every job (a class in a shard) will have its own file and will operate
+    // this file differently depending on the type:
+    //
+    // sequential reads  : will read the file from pos = 0 onwards, back to 0 on EOF
+    // sequential writes : will write the file from pos = 0 onwards, back to 0 on EOF
+    // random reads      : will read the file at random positions, between 0 and EOF
+    // random writes     : will overwrite the file at a random position, between 0 and EOF
+    // append            : will write to the file from pos = EOF onwards, always appending to the end.
+    // cpu               : CPU-only load, file is not created.
+    future<> start(sstring dir) {
+        return do_start(dir);
+    }
+
+    future<> stop() {
+        if (_file) {
+            return _file.close();
+        }
+        return make_ready_future<>();
+    }
+protected:
+    sstring type_str() const {
+        return std::unordered_map<request_type, sstring>{
+            { request_type::seqread, "SEQ READ" },
+            { request_type::seqwrite, "SEQ WRITE" },
+            { request_type::randread, "RAND READ" },
+            { request_type::randwrite, "RAND WRITE" },
+            { request_type::append , "APPEND" },
+            { request_type::cpu , "CPU" },
+        }[_config.type];;
+    }
+
+   const sstring name() const {
+        return _config.name;
+    }
+
+    request_type req_type() const {
+        return _config.type;
+    }
+
+    sstring think_time() const {
+        if (_config.shard_info.think_time == std::chrono::duration<float>(0)) {
+            return "NO think time";
+        } else {
+            return format("{:d} us think time", std::chrono::duration_cast<std::chrono::microseconds>(_config.shard_info.think_time).count());
+        }
+    }
+
+    size_t req_size() const {
+        return _config.shard_info.request_size;
+    }
+
+    unsigned parallelism() const {
+        return _config.shard_info.parallelism;
+    }
+
+    unsigned shares() const {
+        return _config.shard_info.shares;
+    }
+
+    std::chrono::duration<float> total_duration() const {
+        return _total_duration;
+    }
+
+    uint64_t total_data() const {
+        return _data;
+    }
+
+    uint64_t max_latency() const {
+        return max(_latencies);
+    }
+
+    uint64_t average_latency() const {
+        return mean(_latencies);
+    }
+
+    uint64_t quantile_latency(double q) const {
+        return quantile(_latencies, quantile_probability = q);
+    }
+
+    bool is_sequential() const {
+        return (req_type() == request_type::seqread) || (req_type() == request_type::seqwrite);
+    }
+    bool is_random() const {
+        return (req_type() == request_type::randread) || (req_type() == request_type::randwrite);
+    }
+
+    uint64_t get_pos() {
+        uint64_t pos;
+        if (is_random()) {
+            pos = _pos_distribution(random_generator) * req_size();
+        } else {
+            pos = _last_pos + req_size();
+            if (is_sequential() && (pos >= file_data_size)) {
+                pos = 0;
+            }
+        }
+        _last_pos = pos;
+        return pos;
+    }
+
+    void add_result(size_t data, std::chrono::microseconds latency) {
+        _data += data;
+        _latencies(latency.count());
+    }
+
+public:
+    virtual sstring describe_class() = 0;
+    virtual sstring describe_results() = 0;
+};
+
+class io_class_data : public class_data {
+public:
+    io_class_data(job_config cfg) : class_data(std::move(cfg)) {}
+
+    future<> do_start(sstring dir) override {
+        auto fname = format("{}/test-{}-{:d}", dir, name(), this_shard_id());
+        auto flags = open_flags::rw | open_flags::create | open_flags::truncate;
+        if (_config.options.dsync) {
+            flags |= open_flags::dsync;
+        }
+        return open_file_dma(fname, flags).then([this, fname] (auto f) {
+            _file = f;
+            return remove_file(fname);
+        }).then([this, fname] {
+            return do_with(seastar::semaphore(64), [this] (auto& write_parallelism) mutable {
+                auto bufsize = 256ul << 10;
+                auto pos = boost::irange(0ul, (file_data_size / bufsize) + 1);
+                return parallel_for_each(pos.begin(), pos.end(), [this, bufsize, &write_parallelism] (auto pos) mutable {
+                    return get_units(write_parallelism, 1).then([this, bufsize, pos] (auto perm) mutable {
+                        auto bufptr = allocate_aligned_buffer<char>(bufsize, 4096);
+                        auto buf = bufptr.get();
+                        std::uniform_int_distribution<char> fill('@', '~');
+                        memset(buf, fill(random_generator), bufsize);
+                        pos = pos * bufsize;
+                        return _file.dma_write(pos, buf, bufsize).finally([this, bufptr = std::move(bufptr), perm = std::move(perm), pos] {
+                            if ((this->req_type() == request_type::append) && (pos > _last_pos)) {
+                                _last_pos = pos;
+                            }
+                        }).discard_result();
+                    });
+                });
+            });
+        }).then([this] {
+            return _file.flush();
+        });
+    }
+
+    virtual sstring describe_class() override {
+        return fmt::format("{}: {} shares, {}-byte {}, {} concurrent requests, {}", name(), shares(), req_size(), type_str(), parallelism(), think_time());
+    }
+
+    virtual sstring describe_results() override {
+        auto throughput_kbs = (total_data() >> 10) / total_duration().count();
+        sstring result;
+        result += fmt::format("  Throughput         : {:>8} KB/s\n", throughput_kbs);
+        result += fmt::format("  Lat average        : {:>8} usec\n", average_latency());
+        for (auto& q: quantiles) {
+            result += fmt::format("  Lat quantile={:>5} : {:>8} usec\n", q, quantile_latency(q));
+        }
+        result += fmt::format("  Lat max            : {:>8} usec\n", max_latency());
+        return result;
+    }
+};
+
+class read_io_class_data : public io_class_data {
+public:
+    read_io_class_data(job_config cfg) : io_class_data(std::move(cfg)) {}
+
+    future<size_t> issue_request(char *buf) override {
+        return _file.dma_read(this->get_pos(), buf, this->req_size(), _iop);
+    }
+};
+
+class write_io_class_data : public io_class_data {
+public:
+    write_io_class_data(job_config cfg) : io_class_data(std::move(cfg)) {}
+
+    future<size_t> issue_request(char *buf) override {
+        return _file.dma_write(this->get_pos(), buf, this->req_size(), _iop);
+    }
+};
+
+class cpu_class_data : public class_data {
+public:
+    cpu_class_data(job_config cfg) : class_data(std::move(cfg)) {}
+
+    future<> do_start(sstring dir) override {
+        return make_ready_future<>();
+    }
+
+    future<size_t> issue_request(char *buf) override {
+        // We do want the execution time to be a busy loop, and not just a bunch of
+        // continuations until our time is up: by doing this we can also simulate the behavior
+        // of I/O continuations in the face of reactor stalls.
+        auto start  = std::chrono::steady_clock::now();
+        do {
+        } while ((std::chrono::steady_clock::now() - start) < _config.shard_info.execution_time);
+        return make_ready_future<size_t>(1);
+    }
+
+    virtual sstring describe_class() override {
+        auto exec = std::chrono::duration_cast<std::chrono::microseconds>(_config.shard_info.execution_time);
+        return fmt::format("{}: {} shares, {} us CPU execution time, {} concurrent requests, {}", name(), shares(), exec.count(), parallelism(), think_time());
+    }
+
+    virtual sstring describe_results() override {
+        auto throughput = total_data() / total_duration().count();
+        return fmt::format("  Throughput         : {:>8} continuations/s\n", throughput);
+    }
+};
+
+std::unique_ptr<class_data> job_config::gen_class_data() {
+    if (type == request_type::cpu) {
+        return std::make_unique<cpu_class_data>(*this);
+    } else if ((type == request_type::seqread) || (type == request_type::randread)) {
+        return std::make_unique<read_io_class_data>(*this);
+    } else {
+        return std::make_unique<write_io_class_data>(*this);
+    }
+}
+
+/// YAML parsing functions
+namespace YAML {
+template<>
+struct convert<byte_size> {
+    static bool decode(const Node& node, byte_size& bs) {
+        auto str = node.as<std::string>();
+        unsigned shift = 0;
+        if (str.back() == 'B') {
+            str.pop_back();
+            shift = std::unordered_map<char, unsigned>{
+                { 'k', 10 },
+                { 'M', 20 },
+                { 'G', 30 },
+            }[str.back()];
+            str.pop_back();
+        }
+        bs.size = (boost::lexical_cast<size_t>(str) << shift);
+        return bs.size >= 512;
+    }
+};
+
+template<>
+struct convert<duration_time> {
+    static bool decode(const Node& node, duration_time& dt) {
+        auto str = node.as<std::string>();
+        if (str == "0") {
+            dt.time = 0ns;
+            return true;
+        }
+        if (str.back() != 's') {
+            return false;
+        }
+        str.pop_back();
+        std::unordered_map<char, std::chrono::duration<float>> unit = {
+            { 'n', 1ns },
+            { 'u', 1us },
+            { 'm', 1ms },
+        };
+
+        if (unit.count(str.back())) {
+            auto u = str.back();
+            str.pop_back();
+            dt.time = (boost::lexical_cast<size_t>(str) * unit[u]);
+        } else {
+            dt.time = (boost::lexical_cast<size_t>(str) * 1s);
+        }
+        return true;
+    }
+};
+
+template<>
+struct convert<shard_config> {
+    static bool decode(const Node& node, shard_config& shards) {
+        try {
+            auto str = node.as<std::string>();
+            return (str == "all");
+        } catch (YAML::TypedBadConversion<std::string>& e) {
+            shards = shard_config(boost::copy_range<std::unordered_set<unsigned>>(node.as<std::vector<unsigned>>()));
+            return true;
+        }
+        return false;
+    }
+};
+
+template<>
+struct convert<request_type> {
+    static bool decode(const Node& node, request_type& rt) {
+        static std::unordered_map<std::string, request_type> mappings = {
+            { "seqread", request_type::seqread },
+            { "seqwrite", request_type::seqwrite},
+            { "randread", request_type::randread },
+            { "randwrite", request_type::randwrite },
+            { "append", request_type::append},
+            { "cpu", request_type::cpu},
+        };
+        auto reqstr = node.as<std::string>();
+        if (!mappings.count(reqstr)) {
+            return false;
+        }
+        rt = mappings[reqstr];
+        return true;
+    }
+};
+
+template<>
+struct convert<shard_info> {
+    static bool decode(const Node& node, shard_info& sl) {
+        if (node["parallelism"]) {
+            sl.parallelism = node["parallelism"].as<unsigned>();
+        }
+        if (node["shares"]) {
+            sl.shares = node["shares"].as<unsigned>();
+        }
+        if (node["reqsize"]) {
+            sl.request_size = node["reqsize"].as<byte_size>().size;
+        }
+        if (node["think_time"]) {
+            sl.think_time = node["think_time"].as<duration_time>().time;
+        }
+        if (node["execution_time"]) {
+            sl.execution_time = node["execution_time"].as<duration_time>().time;
+        }
+        return true;
+    }
+};
+
+template<>
+struct convert<options> {
+    static bool decode(const Node& node, options& op) {
+        if (node["dsync"]) {
+            op.dsync = node["dsync"].as<bool>();
+        }
+        return true;
+    }
+};
+
+template<>
+struct convert<job_config> {
+    static bool decode(const Node& node, job_config& cl) {
+        cl.name = node["name"].as<std::string>();
+        cl.type = node["type"].as<request_type>();
+        cl.shard_placement = node["shards"].as<shard_config>();
+        if (node["shard_info"]) {
+            cl.shard_info = node["shard_info"].as<shard_info>();
+        }
+        if (node["options"]) {
+            cl.options = node["options"].as<options>();
+        }
+        return true;
+    }
+};
+}
+
+/// Each shard has one context, and the context is responsible for creating the classes that should
+/// run in this shard.
+class context {
+    std::vector<std::unique_ptr<class_data>> _cl;
+
+    sstring _dir;
+    std::chrono::seconds _duration;
+
+    semaphore _finished;
+public:
+    context(sstring dir, std::vector<job_config> req_config, unsigned duration)
+            : _cl(boost::copy_range<std::vector<std::unique_ptr<class_data>>>(req_config
+                | boost::adaptors::filtered([] (auto& cfg) { return cfg.shard_placement.is_set(this_shard_id()); })
+                | boost::adaptors::transformed([] (auto& cfg) { return cfg.gen_class_data(); })
+            ))
+            , _dir(dir)
+            , _duration(duration)
+            , _finished(0)
+    {}
+
+    future<> stop() {
+        return parallel_for_each(_cl, [] (std::unique_ptr<class_data>& cl) {
+            return cl->stop();
+        });
+    }
+
+    future<> start() {
+        return parallel_for_each(_cl, [this] (std::unique_ptr<class_data>& cl) {
+            return cl->start(_dir);
+        });
+    }
+
+    future<> issue_requests() {
+        return parallel_for_each(_cl.begin(), _cl.end(), [this] (std::unique_ptr<class_data>& cl) {
+            return cl->issue_requests(std::chrono::steady_clock::now() + _duration).finally([this] {
+                _finished.signal(1);
+            });
+        });
+    }
+
+    future<> print_stats() {
+        return _finished.wait(_cl.size()).then([this] {
+            fmt::print("Shard {:>2}\n", this_shard_id());
+            auto idx = 0;
+            for (auto& cl: _cl) {
+                fmt::print("Class {:>2} ({})\n", idx++, cl->describe_class());
+                fmt::print("{}\n", cl->describe_results());
+            }
+            return make_ready_future<>();
+        });
+    }
+};
+
+int class_data::idgen() {
+    static thread_local int id = 0;
+    return id++;
+}
+
+int main(int ac, char** av) {
+    namespace bpo = boost::program_options;
+
+    app_template app;
+    auto opt_add = app.add_options();
+    opt_add
+        ("directory", bpo::value<sstring>()->default_value("."), "directory where to execute the test")
+        ("duration", bpo::value<unsigned>()->default_value(10), "for how long (in seconds) to run the test")
+        ("conf", bpo::value<sstring>()->default_value("./conf.yaml"), "YAML file containing benchmark specification")
+    ;
+
+    distributed<context> ctx;
+    return app.run(ac, av, [&] {
+        return seastar::async([&] {
+            auto& opts = app.configuration();
+            auto& directory = opts["directory"].as<sstring>();
+
+            auto fs = file_system_at(directory).get0();
+            if (fs != fs_type::xfs) {
+                throw std::runtime_error(format("This is a performance test. {} is not on XFS", directory));
+            }
+
+            auto& duration = opts["duration"].as<unsigned>();
+            auto& yaml = opts["conf"].as<sstring>();
+            YAML::Node doc = YAML::LoadFile(yaml);
+            auto reqs = doc.as<std::vector<job_config>>();
+
+            parallel_for_each(reqs, [] (auto& r) {
+                return seastar::create_scheduling_group(r.name, r.shard_info.shares).then([&r] (seastar::scheduling_group sg) {
+                    r.shard_info.scheduling_group = sg;
+                });
+            }).get();
+
+            ctx.start(directory, reqs, duration).get0();
+            engine().at_exit([&ctx] {
+                return ctx.stop();
+            });
+            std::cout << "Creating initial files..." << std::endl;
+            ctx.invoke_on_all([] (auto& c) {
+                return c.start();
+            }).get();
+            std::cout << "Starting evaluation..." << std::endl;
+            ctx.invoke_on_all([] (auto& c) {
+                return c.issue_requests();
+            }).get();
+            for (unsigned i = 0; i < smp::count; ++i) {
+                ctx.invoke_on(i, [] (auto& c) {
+                    return c.print_stats();
+                }).get();
+            }
+            ctx.stop().get0();
+        }).or_terminate();
+    });
+}