1467 Make timers MPI compatible (#1468)

reneSchm · jubicker · web-flow · commit c796281bdd8b · 2026-02-24T09:18:03.000+01:00
- Add TimerRegistrar::print_gathered_timers and supporting methods.
- Update example and docs

Co-authored-by: jubicker &lt;113909589+jubicker@users.noreply.github.com&gt;
diff --git a/cpp/examples/performance_timers.cpp b/cpp/examples/performance_timers.cpp
@@ -19,6 +19,9 @@
 */
 #include "memilio/timer/auto_timer.h"
 #include "memilio/timer/table_printer.h"
+#include "memilio/timer/timer_registrar.h"
+#include "memilio/utils/logging.h"
+#include "memilio/utils/miompi.h"
 
 #include <thread> // This is only used for the example load function.
 
@@ -40,8 +43,15 @@ void load()
 
 int main()
 {
-    // Specify the namespace of AutoTimer, so we don't have to repeat it. Do not do this with entire namespaces.
+    mio::set_log_level(mio::LogLevel::info);
+    mio::mpi::init();
+
+    const int comm_rank = mio::mpi::rank(mio::mpi::get_world());
+    const int comm_size = mio::mpi::size(mio::mpi::get_world());
+    // Specify the namespace of AutoTimer and TimerRegistrar, so we don't have to repeat it.
+    // Avoid "using" statements with entire namespaces.
     using mio::timing::AutoTimer;
+    using mio::timing::TimerRegistrar;
 
     // Start immediately timing the main function. An AutoTimer starts timing upon its creation, and ends timing when
     // it is destroyed. This usually happens when a function returns, or a scope indicated by {curly braces} ends.
@@ -54,15 +64,21 @@ int main()
     // the end of the programm. This can be disabled by calling `TimerRegistrar::disable_final_timer_summary()`.
     auto printer = std::make_unique<mio::timing::TablePrinter>();
     printer->set_time_format("{:e}");
-    mio::timing::TimerRegistrar::get_instance().set_printer(std::move(printer));
+    TimerRegistrar::get_instance().set_printer(std::move(printer));
 
-    // To manually print all timers, use `TimerRegistrar::print_timers()`, but make sure that no timers are running.
+    // To manually print all timers, use `TimerRegistrar::print_timers()` (or `TimerRegistrar::print_gathered_timers()`
+    // when using MPI), but make sure that no timers are running.
     // The "main" timer in this example would make that difficult, but you can simply add another scope around it,
     // similar to the "compute loops" timer below.
 
-    const int N = 1000; // Number of iterations. Be wary of increasing this number when using the sleep_for load!
+    // Number of iterations. Be wary of increasing this number when using the sleep_for load!
+    const int total_iterations = 1000;
+    const int N                = total_iterations / comm_size + (comm_rank < (total_iterations % comm_size));
 
-    std::cout << "Num threads: " << mio::omp::get_max_threads() << "\n";
+    if (mio::mpi::is_root()) {
+        mio::log_info("Num ranks: {} - Num threads: {} - Work size per rank: {}", comm_size,
+                      mio::omp::get_max_threads(), N);
+    }
 
     // Open a new scope to time computations.
     {
@@ -100,5 +116,15 @@ int main()
         }
     }
 
+    // For MPI parallel execution, we replace the final timer summary with a manual print. That way, we can gather
+    // timers from all ranks into a single output, instead of each rank printing a separate output. You can also use a
+    // custom printer for computing additional statistics.
+    if (comm_size > 1) {
+        TimerRegistrar::get_instance().disable_final_timer_summary();
+        TimerRegistrar::get_instance().print_gathered_timers(mio::mpi::get_world());
+    }
+
+    mio::mpi::finalize();
+
     return 0;
 }
diff --git a/cpp/memilio/timer/basic_timer.h b/cpp/memilio/timer/basic_timer.h
@@ -20,9 +20,11 @@
 #ifndef MIO_TIMER_BASIC_TIMER_H
 #define MIO_TIMER_BASIC_TIMER_H
 
+#include "memilio/io/io.h"
 #include "memilio/timer/definitions.h"
 
 #include <string_view>
+#include <utility>
 
 namespace mio
 {
@@ -69,6 +71,37 @@ class BasicTimer
         should_be_running(false, "~BasicTimer");
     }
 
+    /**
+     * serialize this.
+     * @see mio::serialize
+     */
+    template <class IOContext>
+    void serialize(IOContext& io) const
+    {
+        auto obj = io.create_object("BasicTimer");
+        obj.add_element("elapsed_time", details::convert_to_ticks(m_elapsed_time));
+    }
+
+    /**
+    * deserialize an object of this class.
+    * @see mio::deserialize
+    */
+    template <class IOContext>
+    static IOResult<BasicTimer> deserialize(IOContext& io)
+    {
+        using Tick = decltype(details::convert_to_ticks(std::declval<DurationType>()));
+        auto obj   = io.expect_object("BasicTimer");
+        auto et    = obj.expect_element("elapsed_time", Tag<Tick>{});
+        return apply(
+            io,
+            [](auto&& et_) {
+                BasicTimer b;
+                b.m_elapsed_time = DurationType{et_};
+                return b;
+            },
+            et);
+    }
+
 private:
     TimeType m_start_time; ///< The last time point at which start() was called
     DurationType m_elapsed_time{0}; ///< The total time spent between starts and stops.
diff --git a/cpp/memilio/timer/definitions.h b/cpp/memilio/timer/definitions.h
@@ -23,7 +23,7 @@
 #include "memilio/utils/mioomp.h"
 
 #include <chrono>
-#include <cstddef>
+#include <ctime>
 
 namespace mio
 {
@@ -42,6 +42,21 @@ using DurationType = std::chrono::steady_clock::duration;
 
 #endif
 
+namespace details
+{
+
+/// @brief Convert a duration to integer ticks. Useful for serialization.
+inline decltype(auto) convert_to_ticks(DurationType duration)
+{
+#ifdef MEMILIO_ENABLE_OPENMP
+    return duration;
+#else
+    return duration.count();
+#endif
+}
+
+} // namespace details
+
 /**
  * @brief Convert a duration to a (floating point) number of seconds.
  * @param[in] duration Any DurationType value, mainly `BasicTimer::get_elapsed_time()`.  
diff --git a/cpp/memilio/timer/list_printer.h b/cpp/memilio/timer/list_printer.h
@@ -21,6 +21,7 @@
 #define MIO_TIMER_LIST_PRINTER_H
 
 #include "memilio/timer/registration.h"
+#include "memilio/utils/compiler_diagnostics.h"
 
 #include <ostream>
 #include <list>
@@ -45,16 +46,16 @@ struct ListPrinter : public Printer {
         const auto indent     = "  ";
         // Write out all timers
         out << "All Timers: " << timer_register.size() << "\n";
-        for (const auto& [name, scope, timer, thread] : timer_register) {
+        for (const auto& [name, scope, timer, thread, rank] : timer_register) {
             out << indent << qualified_name(name, scope) << ": " << std::scientific
-                << time_in_seconds(timer.get_elapsed_time()) << " (" << thread << ")\n";
-            is_multithreaded |= thread > 0;
+                << time_in_seconds(timer.get_elapsed_time()) << " (" << rank << ", " << thread << ")\n";
+            is_multithreaded |= thread > 0 || rank > 0;
         }
         // Write out timers accumulated over threads by name
         if (is_multithreaded) {
             // dedupe list entries from parallel execution
             std::map<std::string, DurationType> deduper;
-            for (const auto& [name, scope, timer, _] : timer_register) {
+            for (const auto& [name, scope, timer, thread, rank] : timer_register) {
                 deduper[qualified_name(name, scope)] += timer.get_elapsed_time();
             }
             out << "Unique Timers (accumulated): " << deduper.size() << "\n";
diff --git a/cpp/memilio/timer/named_timer.h b/cpp/memilio/timer/named_timer.h
@@ -77,7 +77,7 @@ class NamedTimer : public BasicTimer
      */
     NamedTimer()
     {
-        TimerRegistrar::get_instance().add_timer({name(), scope(), *this, mio::omp::get_thread_id()});
+        TimerRegistrar::get_instance().add_timer({name(), scope(), *this, mio::omp::get_thread_id(), 0});
     }
 };
 
diff --git a/cpp/memilio/timer/registration.h b/cpp/memilio/timer/registration.h
@@ -20,6 +20,7 @@
 #ifndef MIO_TIMER_REGISTRATION_H
 #define MIO_TIMER_REGISTRATION_H
 
+#include "memilio/io/default_serialize.h"
 #include "memilio/timer/basic_timer.h"
 
 #include <list>
@@ -30,11 +31,13 @@ namespace mio
 namespace timing
 {
 
+/// @brief Struct used to register ( @see TimerRegistrar ) and print timers ( @see Printer ).
 struct TimerRegistration {
     std::string name;
     std::string scope;
     BasicTimer& timer;
     int thread_id;
+    int rank;
 };
 
 /**
diff --git a/cpp/memilio/timer/table_printer.h b/cpp/memilio/timer/table_printer.h
@@ -206,8 +206,8 @@ class TablePrinter : public Printer
         std::map<std::string, size_t> row_to_index; // map from name to index, used to fill table
         bool is_multithreaded = false; // keep track of whether a thread id > 0 exists
         // map rows from thread 0 first, so the order of timers (mostly) corresponds to their call order
-        for (const auto& [name, scope, _, thread] : timer_register) {
-            if (thread == 0) {
+        for (const auto& [name, scope, timer, thread, rank] : timer_register) {
+            if (thread == 0 && rank == 0) {
                 const std::string qn = qualified_name(name, scope);
                 if (row_to_index.emplace(qn, rows.size()).second) {
                     rows.push_back(qn);
@@ -220,8 +220,8 @@ class TablePrinter : public Printer
         // make a second pass to add timers from other threads
         // this does nothing, if all timers are used on thread 0 at least once
         if (is_multithreaded) {
-            for (auto& [name, scope, _, thread] : timer_register) {
-                if (thread != 0) {
+            for (auto& [name, scope, timer, thread, rank] : timer_register) {
+                if (thread != 0 || rank != 0) {
                     const std::string qn = qualified_name(name, scope);
                     if (row_to_index.emplace(qn, rows.size()).second) {
                         rows.push_back(qn);
@@ -245,7 +245,7 @@ class TablePrinter : public Printer
         }
         // accumulate elapsed time and gather statistics in the table
         // averages are calculated later, using finished values from elapsed and num
-        for (auto& [name, scope, timer, thread] : timer_register) {
+        for (auto& [name, scope, timer, thread, rank] : timer_register) {
             const auto row  = row_to_index[qualified_name(name, scope)];
             const auto time = time_in_seconds(timer.get_elapsed_time());
             table(row, elapsed) += time;
diff --git a/cpp/memilio/timer/timer_registrar.h b/cpp/memilio/timer/timer_registrar.h
@@ -20,14 +20,19 @@
 #ifndef MIO_TIMER_TIMER_REGISTRAR_H
 #define MIO_TIMER_TIMER_REGISTRAR_H
 
+#include "memilio/io/binary_serializer.h"
+#include "memilio/io/default_serialize.h"
+#include "memilio/timer/basic_timer.h"
 #include "memilio/timer/registration.h"
 #include "memilio/timer/table_printer.h"
+#include "memilio/utils/compiler_diagnostics.h"
+#include "memilio/utils/miompi.h"
 
+#include <cassert>
 #include <iostream>
 #include <list>
 #include <memory>
 #include <mutex>
-#include <ostream>
 
 namespace mio
 {
@@ -88,14 +93,35 @@ class TimerRegistrar
     {
         PRAGMA_OMP(single nowait)
         {
-            get_instance().m_printer->print(m_register, out);
+            m_printer->print(m_register, out);
+        }
+    }
+
+    /**
+     * @brief Print all timers gathered on the given MPI Comm using a Printer.
+     * 
+     * By default, uses TablePrinter to write to stdout. The printer can be changed using the set_printer member.
+     *
+     * @param comm An MPI communicator. Make sure this method is called by all ranks on comm!
+     * @param out Any output stream, defaults to std::cout.
+     */
+    void print_gathered_timers(mpi::Comm comm, std::ostream& out = std::cout)
+    {
+        PRAGMA_OMP(single nowait)
+        {
+            std::list<BasicTimer> external_timers; // temporary storage for gathered registrations
+            std::list<TimerRegistration> gathered_register; // combined registrations of all ranks
+            gather_timers(comm, external_timers, gathered_register);
+            if (mpi::is_root()) {
+                m_printer->print(gathered_register, out);
+            }
         }
     }
 
     /// @brief Prevent the TimerRegistrar from calling print_timers on exit from main.
-    void disable_final_timer_summary() const
+    void disable_final_timer_summary()
     {
-        get_instance().m_print_on_death = false;
+        m_print_on_death = false;
     }
 
     /**
@@ -143,6 +169,62 @@ class TimerRegistrar
         }
     }
 
+    /// @brief Gather timers from all ranks, using external_timers as temporary timer storage for gathered_register.
+    void gather_timers(mpi::Comm comm, std::list<BasicTimer>& external_timers,
+                       std::list<TimerRegistration>& gathered_register) const
+    {
+#ifndef MEMILIO_ENABLE_MPI
+        mio::unused(comm, external_timers);
+#endif
+        if (mpi::is_root()) {
+            std::ranges::transform(m_register, std::back_inserter(gathered_register), [](const TimerRegistration& r) {
+                return TimerRegistration{r.name, r.scope, r.timer, r.thread_id, 0};
+            });
+        }
+        if (comm == nullptr) {
+            if (mpi::is_root()) {
+                log_error("Got nullptr as MPI Comm. Only timers on root rank are gathered.");
+            }
+            return;
+        }
+#ifdef MEMILIO_ENABLE_MPI
+        // name, scope, timer, thread_id
+        using GatherableRegistration = std::tuple<std::string, std::string, BasicTimer, int>;
+        int comm_size;
+        MPI_Comm_size(comm, &comm_size);
+
+        if (mpi::is_root()) {
+            for (int snd_rank = 1; snd_rank < comm_size; snd_rank++) { // skip root rank!
+                int bytes_size;
+                MPI_Recv(&bytes_size, 1, MPI_INT, snd_rank, 0, comm, MPI_STATUS_IGNORE);
+                ByteStream bytes(bytes_size);
+                MPI_Recv(bytes.data(), bytes.data_size(), MPI_BYTE, snd_rank, 0, mpi::get_world(), MPI_STATUS_IGNORE);
+
+                auto rec_register = deserialize_binary(bytes, Tag<std::vector<GatherableRegistration>>{});
+                if (!rec_register) {
+                    log_error("Error receiving ensemble results from rank {}.", snd_rank);
+                }
+                std::ranges::transform(
+                    rec_register.value(), std::back_inserter(gathered_register), [&](const GatherableRegistration& r) {
+                        const auto& [name, scope, timer, thread_id] = r;
+                        external_timers.push_back(timer);
+                        return TimerRegistration{name, scope, external_timers.back(), thread_id, snd_rank};
+                    });
+            }
+        }
+        else {
+            std::vector<GatherableRegistration> snd_register;
+            std::ranges::transform(m_register, std::back_inserter(snd_register), [](const TimerRegistration& r) {
+                return GatherableRegistration{r.name, r.scope, r.timer, r.thread_id};
+            });
+            ByteStream bytes = serialize_binary(snd_register);
+            int bytes_size   = int(bytes.data_size());
+            MPI_Send(&bytes_size, 1, MPI_INT, 0, 0, comm);
+            MPI_Send(bytes.data(), bytes.data_size(), MPI_BYTE, 0, 0, comm);
+        }
+#endif
+    }
+
     std::unique_ptr<Printer> m_printer = std::make_unique<TablePrinter>(); ///< A printer to visualize all timers.
     bool m_print_on_death              = true; ///< Whether to call m_printer during the destructor.
     std::list<TimerRegistration> m_register; ///< List that allows access to timers without having their name.
diff --git a/cpp/memilio/utils/miompi.cpp b/cpp/memilio/utils/miompi.cpp
diff --git a/cpp/memilio/utils/miompi.h b/cpp/memilio/utils/miompi.h
diff --git a/cpp/tests/test_timers.cpp b/cpp/tests/test_timers.cpp
diff --git a/docs/source/cpp/performance_monitoring.rst b/docs/source/cpp/performance_monitoring.rst

Original file line number	Diff line number	Diff line change
`@@ -77,7 +77,7 @@ class NamedTimer : public BasicTimer`
`77`	`77`	`*/`
`78`	`78`	`NamedTimer()`
`79`	`79`	`{`
`80`		`- TimerRegistrar::get_instance().add_timer({name(), scope(), *this, mio::omp::get_thread_id()});`
	`80`	`+ TimerRegistrar::get_instance().add_timer({name(), scope(), *this, mio::omp::get_thread_id(), 0});`
`81`	`81`	`}`
`82`	`82`	`};`
`83`	`83`