Add per-Task cpu time metric

initialize to zero

make new task field visible from Julia

add start time

fix typo

add test

add a wait

import `LinearAlgebra` for `peakflops`

update last scheduled on task finish as well

no need to update last scheduled in finish

add test

fix test

Add per-task wall-time

Test individual task cpu_time less than wall_time

More tests

Move task timings mostly to julia

Record cpu time on entrance to `wait/yield`

Rename 'scheduled_at' -> '[en/de]queued_at'

Ability to enable/disable task timings globally

fixup whitespace

Enable task timing in test

Enable task timing for root task

Prevent `task_timing(false)` decrementing below zero

Change task-timing flag to require yes/no arg

Rename `timings`->`metrics`, `dequeued`->`started_running`

Update task-state-transition comments

Remove unused debug function

Add NEWS

Add fallback recording of cpu time in `wait()`

Instrument async io

Record task cpu time in `wait()`

Make task metrics flag const and counters atomic

Mark the new APIs experimental

Return task metrics as Int or nothing if disabled

Test metrics updating as expected

More tests

base/experimental.jl

@@ -368,4 +368,74 @@ adding them to the global method table.
 """
 :@MethodTable
 
+### Task metrics
+
+"""
+    Base.Experimental.task_metrics(::Bool)
+
+Enable or disable the collection of per-task metrics.
+A `Task` created when `Base.task_metrics(true)` is in effect will have
+[`Base.Experimental.task_cpu_time_ns`](@ref) and [`Base.Experimental.task_wall_time_ns`](@ref)
+timing information available.
+
+!!! note
+    Task metrics can be enabled at start-up via the `--task-metrics=yes` command line option.
+"""
+function task_metrics(b::Bool)
+    if b
+        ccall(:jl_task_metrics_enable, Cvoid, ())
+    else
+        ccall(:jl_task_metrics_disable, Cvoid, ())
+    end
+    return nothing
+end
+
+"""
+    Base.Experimental.task_cpu_time_ns(t::Task) -> Union{Int, Nothing}
+
+Return the total nanoseconds that the task `t` has spent running.
+See also [`Base.Experimental.task_wall_time_ns`](@ref).
+
+Will be `nothing` if task timings are not enabled.
+See [`Base.Experimental.task_metrics`](@ref).
+
+!!! note "This metric is from the Julia scheduler"
+    A task may be running on an OS thread that is descheduled by the OS
+    scheduler, this time still counts towards the metric.
+
+!!! compat "Julia 1.12"
+    This method was added in Julia 1.12.
+"""
+function task_cpu_time_ns(t::Task)
+    t.metrics_enabled || return nothing
+    if t.last_started_running_at == 0
+        return Int(t.cpu_time_ns)
+    else
+        return Int(t.cpu_time_ns + (time_ns() - t.last_started_running_at))
+    end
 end
+
+"""
+    Base.Experimental.task_wall_time_ns(t::Task) -> Union{Int, Nothing}
+
+Return the total nanoseconds that the task `t` was runnable.
+This is the time since the task entered the run queue until the time at which it completed,
+or until the current time if the task has not yet completed.
+See also [`task_cpu_time_ns`](@ref).
+
+Will be `nothing` if task timings are not enabled.
+See [`Base.task_metrics`](@ref).
+
+!!! compat "Julia 1.12"
+    This method was added in Julia 1.12.
+"""
+function task_wall_time_ns(t::Task)
+    t.metrics_enabled || return nothing
+    start_at = t.first_enqueued_at
+    start_at == 0 && return 0
+    end_at = t.finished_at
+    end_at == 0 && return Int(time_ns() - start_at)
+    return Int(end_at - start_at)
+end
+
+end # module

base/options.jl

@@ -60,6 +60,7 @@ struct JLOptions
     heap_size_hint::UInt64
     trace_compile_timing::Int8
     safe_crash_log_file::Ptr{UInt8}
+    task_metrics::Int8
 end
 
 # This runs early in the sysimage != is not defined yet

base/task.jl

@@ -810,7 +810,11 @@ function enq_work(t::Task)
     return t
 end
 
-schedule(t::Task) = enq_work(t)
+function schedule(t::Task)
+    # [task] created -scheduled-> wait_time
+    maybe_record_enqueued!(t)
+    enq_work(t)
+end
 
 """
     schedule(t::Task, [val]; error=false)
@@ -857,6 +861,8 @@ function schedule(t::Task, @nospecialize(arg); error=false)
         t.queue === nothing || Base.error("schedule: Task not runnable")
         setfield!(t, :result, arg)
     end
+    # [task] created -scheduled-> wait_time
+    maybe_record_enqueued!(t)
     enq_work(t)
     return t
 end
@@ -888,7 +894,13 @@ A fast, unfair-scheduling version of `schedule(t, arg); yield()` which
 immediately yields to `t` before calling the scheduler.
 """
 function yield(t::Task, @nospecialize(x=nothing))
-    (t._state === task_state_runnable && t.queue === nothing) || error("yield: Task not runnable")
+    current = current_task()
+    # [task] user_time -yield-> wait_time
+    record_cpu_time!(current)
+    t === current && throw(ConcurrencyViolationError("Cannot yield to currently running task!"))
+    (t._state === task_state_runnable && t.queue === nothing) || throw(ConcurrencyViolationError("yield: Task not runnable"))
+    # [task] created -scheduled-> wait_time
+    maybe_record_enqueued!(t)
     t.result = x
     enq_work(current_task())
     set_next_task(t)
@@ -904,13 +916,17 @@ call to `yieldto`. This is a low-level call that only switches tasks, not consid
 or scheduling in any way. Its use is discouraged.
 """
 function yieldto(t::Task, @nospecialize(x=nothing))
+    # [task] user_time -yield-> wait_time
+    record_cpu_time!(current_task())
     # TODO: these are legacy behaviors; these should perhaps be a scheduler
     # state error instead.
     if t._state === task_state_done
         return x
     elseif t._state === task_state_failed
         throw(t.result)
     end
+    # [task] created -scheduled-unfairly-> wait_time
+    maybe_record_enqueued!(t)
     t.result = x
     set_next_task(t)
     return try_yieldto(identity)
@@ -924,6 +940,11 @@ function try_yieldto(undo)
         rethrow()
     end
     ct = current_task()
+    # [task] wait_time -(re)started-> user_time
+    if ct.metrics_enabled
+        @assert ct.last_started_running_at == 0
+        @atomic :monotonic ct.last_started_running_at = time_ns()
+    end
     if ct._isexception
         exc = ct.result
         ct.result = nothing
@@ -937,6 +958,10 @@ end
 
 # yield to a task, throwing an exception in it
 function throwto(t::Task, @nospecialize exc)
+    # [task] user_time -yield-> wait_time
+    record_cpu_time!(current_task())
+    # [task] created -scheduled-unfairly-> wait_time
+    maybe_record_enqueued!(t)
     t.result = exc
     t._isexception = true
     set_next_task(t)
@@ -989,6 +1014,8 @@ checktaskempty = Partr.multiq_check_empty
 end
 
 function wait()
+    # [task] user_time -yield-or-done-> wait_time
+    record_cpu_time!(current_task())
     GC.safepoint()
     W = workqueue_for(Threads.threadid())
     poptask(W)
@@ -1003,3 +1030,24 @@ if Sys.iswindows()
 else
     pause() = ccall(:pause, Cvoid, ())
 end
+
+# update the `cpu_time_ns` field of `t` to include the time since it last started running.
+function record_cpu_time!(t::Task)
+    if t.metrics_enabled
+        stopped_at = t.finished_at == 0 ? time_ns() : t.finished_at
+        @assert t.last_started_running_at != 0
+        @atomic :monotonic t.cpu_time_ns += stopped_at - t.last_started_running_at
+        # set to 0 to indicate that the task is not running
+        @atomic :monotonic t.last_started_running_at = 0
+    end
+    return t
+end
+# if this is the first time `t` has been added to the run queue
+# (or the first time it has been unfairly yielded to without being added to the run queue)
+# then set the `first_enqueued_at` field to the current time.
+function maybe_record_enqueued!(t::Task)
+    if t.metrics_enabled && t.first_enqueued_at == 0
+        @atomic :monotonic t.first_enqueued_at = time_ns()
+    end
+    return t
+end

doc/man/julia.1

@@ -271,6 +271,9 @@ Print precompile statements for methods compiled during execution or save to a p
 If --trace-compile is enabled show how long each took to compile in ms
 
 .TP
+--task-metrics={yes|no*}
+Enable the collection of per-task metrics.
+
 -image-codegen
 Force generate code in imaging mode
 
@@ -281,6 +284,5 @@ See https://docs.julialang.org/en/v1/manual/environment-variables/
 Please report any bugs using the GitHub issue tracker:
 https://github.com/julialang/julia/issues?state=open
 
-
 .SH AUTHORS
 Contributors: https://github.com/JuliaLang/julia/graphs/contributors

doc/src/manual/command-line-interface.md

@@ -130,6 +130,7 @@ The following is a complete list of command-line switches available when launchi
 |`--code-coverage=tracefile.info`       |Append coverage information to the LCOV tracefile (filename supports format tokens).|
 |`--track-allocation[={none*\|user\|all}]` |Count bytes allocated by each source line (omitting setting is equivalent to "user")|
 |`--track-allocation=@<path>`           |Count bytes but only in files that fall under the given file path/directory. The `@` prefix is required to select this option. A `@` with no path will track the current directory.|
+|`--task-metrics={yes\|no*}`             |Enable the collection of per-task metrics|
 |`--bug-report=KIND`                    |Launch a bug report session. It can be used to start a REPL, run a script, or evaluate expressions. It first tries to use BugReporting.jl installed in current environment and falls back to the latest compatible BugReporting.jl if not. For more information, see `--bug-report=help`.|
 |`--compile={yes*\|no\|all\|min}`       |Enable or disable JIT compiler, or request exhaustive or minimal compilation|
 |`--output-o <name>`                    |Generate an object file (including system image data)|

src/init.c

@@ -851,6 +851,10 @@ JL_DLLEXPORT void julia_init(JL_IMAGE_SEARCH rel)
 #if defined(_COMPILER_GCC_) && __GNUC__ >= 12
 #pragma GCC diagnostic ignored "-Wdangling-pointer"
 #endif
+    if (jl_options.task_metrics == JL_OPTIONS_TASK_METRICS_ON) {
+        // enable before creating the root task so it gets timings too.
+        jl_atomic_fetch_add(&jl_task_metrics_enabled, 1);
+    }
     // warning: this changes `jl_current_task`, so be careful not to call that from this function
     jl_task_t *ct = jl_init_root_task(ptls, stack_lo, stack_hi);
 #pragma GCC diagnostic pop

src/jlapi.c

@@ -509,6 +509,28 @@ JL_DLLEXPORT uint64_t jl_cumulative_recompile_time_ns(void)
     return jl_atomic_load_relaxed(&jl_cumulative_recompile_time);
 }
 
+/**
+ * @brief Enable per-task timing.
+ */
+JL_DLLEXPORT void jl_task_metrics_enable(void)
+{
+    // Increment the flag to allow reentrant callers.
+    jl_atomic_fetch_add(&jl_task_metrics_enabled, 1);
+}
+
+/**
+ * @brief Disable per-task timing.
+ */
+JL_DLLEXPORT void jl_task_metrics_disable(void)
+{
+    // Prevent decrementing the counter below zero
+    uint8_t enabled = jl_atomic_load_relaxed(&jl_task_metrics_enabled);
+    while (enabled > 0) {
+        if (jl_atomic_cmpswap(&jl_task_metrics_enabled, &enabled, enabled-1))
+            break;
+    }
+}
+
 JL_DLLEXPORT void jl_get_fenv_consts(int *ret)
 {
     ret[0] = FE_INEXACT;

src/jloptions.c

@@ -93,6 +93,7 @@ JL_DLLEXPORT void jl_init_options(void)
                         0, // heap-size-hint
                         0, // trace_compile_timing
                         NULL, // safe_crash_log_file
+                        0, // task_metrics
     };
     jl_options_initialized = 1;
 }
@@ -206,7 +207,7 @@ static const char opts_hidden[]  =
     " --strip-metadata         Remove docstrings and source location info from system image\n"
     " --strip-ir               Remove IR (intermediate representation) of compiled functions\n\n"
 
-    // compiler debugging (see the devdocs for tips on using these options)
+    // compiler debugging and experimental (see the devdocs for tips on using these options)
     " --output-unopt-bc <name> Generate unoptimized LLVM bitcode (.bc)\n"
     " --output-bc <name>       Generate LLVM bitcode (.bc)\n"
     " --output-asm <name>      Generate an assembly file (.s)\n"
@@ -215,6 +216,7 @@ static const char opts_hidden[]  =
     " --trace-compile={stderr,name}\n"
     "                          Print precompile statements for methods compiled during execution or save to a path\n"
     " --trace-compile-timing   If --trace-compile is enabled show how long each took to compile in ms\n"
+    " --task-metrics={yes|no*} Enable collection of per-task timing data.\n"
     " --image-codegen          Force generate code in imaging mode\n"
     " --permalloc-pkgimg={yes|no*} Copy the data section of package images into memory\n"
 ;
@@ -239,6 +241,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
            opt_trace_compile,
            opt_trace_compile_timing,
            opt_trace_dispatch,
+           opt_task_metrics,
            opt_math_mode,
            opt_worker,
            opt_bind_to,
@@ -316,6 +319,7 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
         { "polly",           required_argument, 0, opt_polly },
         { "trace-compile",   required_argument, 0, opt_trace_compile },
         { "trace-dispatch",  required_argument, 0, opt_trace_dispatch },
+        { "task-metrics",    required_argument, 0, opt_task_metrics },
         { "math-mode",       required_argument, 0, opt_math_mode },
         { "handle-signals",  required_argument, 0, opt_handle_signals },
         // hidden command line options
@@ -872,6 +876,14 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
             if (jl_options.safe_crash_log_file == NULL)
                 jl_error("julia: failed to allocate memory for --safe-crash-log-file");
             break;
+        case opt_task_metrics:
+            if (!strcmp(optarg, "no"))
+                jl_options.task_metrics = JL_OPTIONS_TASK_METRICS_OFF;
+            else if (!strcmp(optarg, "yes"))
+                jl_options.task_metrics = JL_OPTIONS_TASK_METRICS_ON;
+            else
+                jl_errorf("julia: invalid argument to --task-metrics={yes|no} (%s)", optarg);
+            break;
         default:
             jl_errorf("julia: unhandled option -- %c\n"
                       "This is a bug, please report it.", c);

src/jloptions.h

@@ -64,6 +64,7 @@ typedef struct {
     uint64_t heap_size_hint;
     int8_t trace_compile_timing;
     const char *safe_crash_log_file;
+    int8_t task_metrics;
 } jl_options_t;
 
 #endif

src/jltypes.c

@@ -3222,7 +3222,7 @@ void jl_init_types(void) JL_GC_DISABLED
                         NULL,
                         jl_any_type,
                         jl_emptysvec,
-                        jl_perm_symsvec(16,
+                        jl_perm_symsvec(21,
                                         "next",
                                         "queue",
                                         "storage",
@@ -3238,8 +3238,13 @@ void jl_init_types(void) JL_GC_DISABLED
                                         "_state",
                                         "sticky",
                                         "_isexception",
-                                        "priority"),
-                        jl_svec(16,
+                                        "priority",
+                                        "metrics_enabled",
+                                        "first_enqueued_at",
+                                        "last_started_running_at",
+                                        "cpu_time_ns",
+                                        "finished_at"),
+                        jl_svec(21,
                                 jl_any_type,
                                 jl_any_type,
                                 jl_any_type,
@@ -3255,12 +3260,23 @@ void jl_init_types(void) JL_GC_DISABLED
                                 jl_uint8_type,
                                 jl_bool_type,
                                 jl_bool_type,
-                                jl_uint16_type),
+                                jl_uint16_type,
+                                jl_bool_type,
+                                jl_uint64_type,
+                                jl_uint64_type,
+                                jl_uint64_type,
+                                jl_uint64_type),
                         jl_emptysvec,
                         0, 1, 6);
     XX(task);
     jl_value_t *listt = jl_new_struct(jl_uniontype_type, jl_task_type, jl_nothing_type);
     jl_svecset(jl_task_type->types, 0, listt);
+    // Set field 17 (metrics_enabled) as const
+    // Set fields 13 (_state) and 18-21 (metric counters) as atomic
+    const static uint32_t task_constfields[1]  = { 0b000010000000000000000 };
+    const static uint32_t task_atomicfields[1] = { 0b111100001000000000000 };
+    jl_task_type->name->constfields = task_constfields;
+    jl_task_type->name->atomicfields = task_atomicfields;
 
     jl_binding_type =
         jl_new_datatype(jl_symbol("Binding"), core, jl_any_type, jl_emptysvec,