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Kernel+Profiler: Track lost time between profiler timer ticks

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We can lose profiling timer events for a few reasons, for example
disabled interrupts or system slowness. This accounts for lost
time between CPU samples by adding a field lost_samples to each
profiling event which tracks how many samples were lost immediately
preceding the event.
This commit is contained in:
Gunnar Beutner 2021-05-13 22:14:07 +02:00 • committed by Andreas Kling
parent 8614d18956
commit c41f13f10b
8 changed files with 30 additions and 11 deletions
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15
Kernel/PerformanceManager.h
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@ -34,7 +34,7 @@ public:
if (g_profiling_all_threads) {
VERIFY(g_global_perf_events);
[[maybe_unused]] auto rc = g_global_perf_events->append_with_eip_and_ebp(
process.pid(), 0, 0, 0, PERF_EVENT_PROCESS_EXIT, 0, 0, nullptr);
process.pid(), 0, 0, 0, PERF_EVENT_PROCESS_EXIT, 0, 0, 0, nullptr);
}
}
@ -52,7 +52,7 @@ public:
}
}
inline static void add_cpu_sample_event(Thread& current_thread, const RegisterState& regs)
inline static void add_cpu_sample_event(Thread& current_thread, const RegisterState& regs, u32 lost_time)
{
PerformanceEventBuffer* perf_events = nullptr;
@ -67,7 +67,7 @@ public:
if (perf_events) {
[[maybe_unused]] auto rc = perf_events->append_with_eip_and_ebp(
current_thread.pid(), current_thread.tid(),
regs.eip, regs.ebp, PERF_EVENT_SAMPLE, 0, 0, nullptr);
regs.eip, regs.ebp, PERF_EVENT_SAMPLE, lost_time, 0, 0, nullptr);
}
}
@ -87,13 +87,20 @@ public:
inline static void timer_tick(RegisterState const& regs)
{
static Time last_wakeup;
auto now = kgettimeofday();
constexpr auto ideal_interval = Time::from_microseconds(1000'000 / OPTIMAL_PROFILE_TICKS_PER_SECOND_RATE);
auto expected_wakeup = last_wakeup + ideal_interval;
auto delay = (now > expected_wakeup) ? now - expected_wakeup : Time::from_microseconds(0);
last_wakeup = now;
auto current_thread = Thread::current();
// FIXME: We currently don't collect samples while idle.
// That will be an interesting mode to add in the future. :^)
if (!current_thread || current_thread == Processor::current().idle_thread())
return;
PerformanceManager::add_cpu_sample_event(*current_thread, regs);
auto lost_samples = delay.to_microseconds() / ideal_interval.to_microseconds();
PerformanceManager::add_cpu_sample_event(*current_thread, regs, lost_samples);
}
};