5_perf.cpp

perf example.

perf example.

/*
 * SPDX-FileCopyrightText: 2019-2026 Jochem Rutgers
 *
 * SPDX-License-Identifier: CC0-1.0
 */
 
#include <zth>
 
// To generate VCD output, run this example like:
//   ZTH_CONFIG_DO_PERF_EVENT=1 examples/5_perf
// Play around by setting ZTH_CONFIG_ENABLE_DEBUG_PRINT=[01] or running the
// Debug or Release build.
 
static void do_work(int amount)
{
        zth::Timestamp end = zth::Timestamp::now() + 1e-1f * (float)amount;
        while(!end.hasPassed())
                ; // busy wait
}
 
void scheduling()
{
        // When ZTH_CONFIG_DO_PERF_EVENT is set to 1, the perf API is enabled,
        // which includes generating a VCD file.  This VCD file shows every
        // fiber in the system and indicates the state of every fiber at every
        // instance in time.  This allows you to investigate the scheduling
        // behavior of fibers.  The state of every fiber is indicated in IEEE
        // 1164 std_logic format, using the following values:
        // - U (undefined): the fiber has not been created yet
        // - L (low): the fiber has been created, but not initialized
        //   (zth::Fiber::New state)
        // - 0: the fiber is ready (zth::Fiber::Ready state), but not actually
        //   using the CPU
        // - 1: the fiber is currently running, which can be only one fiber per
        //   zth::Worker.
        // - W (weak): the fiber is blocked (zth::Fiber::Waiting)
        //   (sleeping/poll/blocking read/etc.)
        // - Z (high impedance): the fiber is suspended (zth::Fiber::Suspended)
        // - X (unknown): the fiber is dead (zth::Fiber::Dead), but not cleaned up
        // - - (don't care): the fiber has been cleaned up, which also indicates
        //   that the zth::Fiber object has been deleted.
 
        // The VCD file will show for this fiber the following sequence:
        //   U L 1 W 0 1 X -
        // The Waiter (usually fiber #3) manages the mnap of below.  Open the
        // generated VCD file, using gtkwave, for example.  Try to understand
        // the relation between fibers in the VCD.
        zth::mnap(10);
}
zth_fiber(scheduling)
 
void measure()
{
        // This example measures the duration of a task. There are several
        // helpful functions for this.  First, take a time stamp.
        // zth::Timestamp::now() is (supposed to be) fast and is used
        // everywhere, so go ahead and safe t0.
        zth::Timestamp t0 = zth::Timestamp::now();
 
        // perf_mark() allow you to put very efficiently a marker (which must
        // be a C string literal) in the VCD log at the current time. We are
        // going to use this to double check our measurements in the VCD file.
        // This is like printf()-debugging, but with accurate timing
        // information.
        zth::perf_mark("do_work(1)");
 
        // Go do some lengthy work.
        do_work(1);
 
        // Set another marker.
        zth::perf_mark("do_work(1) done");
 
        // Compute time difference. This is not completely fair, as this
        // includes running perf_mark() twice.
        zth::TimeInterval dt = zth::Timestamp::now() - t0;
 
        // Let us format some log string.
        zth::string log = zth::format("do_work(1) took %s", dt.str().c_str());
        // Put the log string also in the VCD file...
        zth::perf_log("%s", log.c_str());
        // ...and to stdout.
        printf("%s\n", log.c_str());
 
        // Open the generated VCD file.  Every fiber has two 'signals': the
        // schedule state of the fiber, and a string with logs.  The
        // perf_mark() and perf_log() should show up there.  Try to measure the
        // length between the perf_mark()s in the VCD log string and compare it
        // with the measured time interval.
}
zth_fiber(measure)
 
void stack()
{
        // Make a snapshot of the current stack backtrace.
        zth::Backtrace bt;
        // Print it to stdout.
        bt.print();
 
        // Make another snapshot.
        zth::Backtrace bt2;
        bt2.printDelta(bt);
}
zth_fiber(stack)
 
 
 
int main_fiber(int /*argc*/, char** /*argv*/)
{
        zth_async scheduling();
        zth_async measure();
        zth_async stack();
        return 0;
}