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Everywhere: Improve CPU usage calculation

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As threads come and go, we can't simply account for how many time
slices the threads at any given point may have been using. We need to
also account for threads that have since disappeared. This means we
also need to track how many time slices we have expired globally.

However, because this doesn't account for context switches outside of
the system timer tick values may still be under-reported. To solve this
we will need to track more accurate time information on each context
switch.

This also fixes top's cpu usage calculation which was still based on
the number of context switches.

Fixes #6473
This commit is contained in:
Tom 2021-07-14 12:05:59 -06:00 • committed by Andreas Kling
parent ef85c4f747
commit 7e77a2ec40
17 changed files with 132 additions and 83 deletions
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26
Userland/Applets/ResourceGraph/main.cpp
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@ -45,14 +45,12 @@ private:
{
switch (m_graph_type) {
case GraphType::CPU: {
unsigned busy;
unsigned idle;
if (get_cpu_usage(busy, idle)) {
unsigned busy_diff = busy - m_last_cpu_busy;
unsigned idle_diff = idle - m_last_cpu_idle;
u64 busy, idle, scheduled_diff;
if (get_cpu_usage(busy, idle, scheduled_diff)) {
auto busy_diff = busy - m_last_cpu_busy;
m_last_cpu_busy = busy;
m_last_cpu_idle = idle;
float cpu = (float)busy_diff / (float)(busy_diff + idle_diff);
float cpu = scheduled_diff > 0 ? (float)busy_diff / (float)scheduled_diff : 0;
m_history.enqueue(cpu);
m_tooltip = String::formatted("CPU usage: {:.1}%", 100 * cpu);
} else {
@ -120,16 +118,21 @@ private:
}
}
bool get_cpu_usage(unsigned& busy, unsigned& idle)
bool get_cpu_usage(u64& busy, u64& idle, u64& scheduled_diff)
{
busy = 0;
idle = 0;
scheduled_diff = 0;
auto all_processes = Core::ProcessStatisticsReader::get_all(m_proc_all);
if (!all_processes.has_value() || all_processes.value().is_empty())
if (!all_processes.has_value() || all_processes.value().processes.is_empty())
return false;
for (auto& it : all_processes.value()) {
if (m_last_total_sum.has_value())
scheduled_diff = all_processes->total_ticks_scheduled - m_last_total_sum.value();
m_last_total_sum = all_processes->total_ticks_scheduled;
for (auto& it : all_processes.value().processes) {
for (auto& jt : it.threads) {
if (it.pid == 0)
idle += jt.ticks_user + jt.ticks_kernel;
@ -174,8 +177,9 @@ private:
Gfx::Color m_graph_color;
Gfx::Color m_graph_error_color;
CircularQueue<float, history_size> m_history;
unsigned m_last_cpu_busy { 0 };
unsigned m_last_cpu_idle { 0 };
u64 m_last_cpu_busy { 0 };
u64 m_last_cpu_idle { 0 };
Optional<u64> m_last_total_sum;
String m_tooltip;
RefPtr<Core::File> m_proc_all;
RefPtr<Core::File> m_proc_mem;