Kernel: Improve time keeping and dramatically reduce interrupt load

This implements a number of changes related to time:
* If a HPET is present, it is now used only as a system timer, unless
  the Local APIC timer is used (in which case the HPET timer will not
  trigger any interrupts at all).
* If a HPET is present, the current time can now be as accurate as the
  chip can be, independently from the system timer. We now query the
  HPET main counter for the current time in CPU #0's system timer
  interrupt, and use that as a base line. If a high precision time is
  queried, that base line is used in combination with quering the HPET
  timer directly, which should give a much more accurate time stamp at
  the expense of more overhead. For faster time stamps, the more coarse
  value based on the last interrupt will be returned. This also means
  that any missed interrupts should not cause the time to drift.
* The default system interrupt rate is reduced to about 250 per second.
* Fix calculation of Thread CPU usage by using the amount of ticks they
  used rather than the number of times a context switch happened.
* Implement CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE and use it
  for most cases where precise timestamps are not needed.

5 files changed, 14 insertions, 8 deletions

diff --git a/Libraries/LibCore/ElapsedTimer.cpp b/Libraries/LibCore/ElapsedTimer.cpp
index 1d7d37009d..9d0fc95378 100644
--- a/Libraries/LibCore/ElapsedTimer.cpp
+++ b/Libraries/LibCore/ElapsedTimer.cpp
@@ -36,7 +36,7 @@ void ElapsedTimer::start()
 {
     m_valid = true;
     timespec now_spec;
-    clock_gettime(CLOCK_MONOTONIC, &now_spec);
+    clock_gettime(m_precise ? CLOCK_MONOTONIC : CLOCK_MONOTONIC_COARSE, &now_spec);
     m_origin_time.tv_sec = now_spec.tv_sec;
     m_origin_time.tv_usec = now_spec.tv_nsec / 1000;
 }
@@ -46,7 +46,7 @@ int ElapsedTimer::elapsed() const
     ASSERT(is_valid());
     struct timeval now;
     timespec now_spec;
-    clock_gettime(CLOCK_MONOTONIC, &now_spec);
+    clock_gettime(m_precise ? CLOCK_MONOTONIC : CLOCK_MONOTONIC_COARSE, &now_spec);
     now.tv_sec = now_spec.tv_sec;
     now.tv_usec = now_spec.tv_nsec / 1000;
     struct timeval diff;
diff --git a/Libraries/LibCore/ElapsedTimer.h b/Libraries/LibCore/ElapsedTimer.h
index 4759c0ede0..224eb139e3 100644
--- a/Libraries/LibCore/ElapsedTimer.h
+++ b/Libraries/LibCore/ElapsedTimer.h
@@ -32,7 +32,10 @@ namespace Core {
 
 class ElapsedTimer {
 public:
-    ElapsedTimer() { }
+    ElapsedTimer(bool precise = false)
+        : m_precise(precise)
+    {
+    }
 
     bool is_valid() const { return m_valid; }
     void start();
@@ -41,6 +44,7 @@ public:
     const struct timeval& origin_time() const { return m_origin_time; }
 
 private:
+    bool m_precise { false };
     bool m_valid { false };
     struct timeval m_origin_time {
         0, 0
diff --git a/Libraries/LibCore/EventLoop.cpp b/Libraries/LibCore/EventLoop.cpp
index 646e8d3e8c..4e45d3852f 100644
--- a/Libraries/LibCore/EventLoop.cpp
+++ b/Libraries/LibCore/EventLoop.cpp
@@ -580,7 +580,7 @@ retry:
         auto next_timer_expiration = get_next_timer_expiration();
         if (next_timer_expiration.has_value()) {
             timespec now_spec;
-            clock_gettime(CLOCK_MONOTONIC, &now_spec);
+            clock_gettime(CLOCK_MONOTONIC_COARSE, &now_spec);
             now.tv_sec = now_spec.tv_sec;
             now.tv_usec = now_spec.tv_nsec / 1000;
             timeval_sub(next_timer_expiration.value(), now, timeout);
@@ -631,7 +631,7 @@ try_select_again:
 
     if (!s_timers->is_empty()) {
         timespec now_spec;
-        clock_gettime(CLOCK_MONOTONIC, &now_spec);
+        clock_gettime(CLOCK_MONOTONIC_COARSE, &now_spec);
         now.tv_sec = now_spec.tv_sec;
         now.tv_usec = now_spec.tv_nsec / 1000;
     }
@@ -709,7 +709,7 @@ int EventLoop::register_timer(Object& object, int milliseconds, bool should_relo
     timer->interval = milliseconds;
     timeval now;
     timespec now_spec;
-    clock_gettime(CLOCK_MONOTONIC, &now_spec);
+    clock_gettime(CLOCK_MONOTONIC_COARSE, &now_spec);
     now.tv_sec = now_spec.tv_sec;
     now.tv_usec = now_spec.tv_nsec / 1000;
     timer->reload(now);
diff --git a/Libraries/LibCore/ProcessStatisticsReader.cpp b/Libraries/LibCore/ProcessStatisticsReader.cpp
index 69928d5b46..5a0ff949c6 100644
--- a/Libraries/LibCore/ProcessStatisticsReader.cpp
+++ b/Libraries/LibCore/ProcessStatisticsReader.cpp
@@ -85,7 +85,8 @@ HashMap<pid_t, Core::ProcessStatistics> ProcessStatisticsReader::get_all()
             thread.times_scheduled = thread_object.get("times_scheduled").to_u32();
             thread.name = thread_object.get("name").to_string();
             thread.state = thread_object.get("state").to_string();
-            thread.ticks = thread_object.get("ticks").to_u32();
+            thread.ticks_user = thread_object.get("ticks_user").to_u32();
+            thread.ticks_kernel = thread_object.get("ticks_kernel").to_u32();
             thread.cpu = thread_object.get("cpu").to_u32();
             thread.priority = thread_object.get("priority").to_u32();
             thread.effective_priority = thread_object.get("effective_priority").to_u32();
diff --git a/Libraries/LibCore/ProcessStatisticsReader.h b/Libraries/LibCore/ProcessStatisticsReader.h
index 3afcac4f60..9c3bd93a80 100644
--- a/Libraries/LibCore/ProcessStatisticsReader.h
+++ b/Libraries/LibCore/ProcessStatisticsReader.h
@@ -35,7 +35,8 @@ namespace Core {
 struct ThreadStatistics {
     pid_t tid;
     unsigned times_scheduled;
-    unsigned ticks;
+    unsigned ticks_user;
+    unsigned ticks_kernel;
     unsigned syscall_count;
     unsigned inode_faults;
     unsigned zero_faults;