Kernel: Prune uninteresting kernel frames from profiling samples

Start capturing the sample stacks at the EIP/EBP of the pre-empted thread instead of capturing EBP in the sampling function itself.
Cnidarias · Jan 17, 2021 · 647cfcb · 647cfcb
1 parent bf07190
commit 647cfcb
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Showing 3 changed files with 12 additions and 5 deletions.
diff --git a/Kernel/PerformanceEventBuffer.cpp b/Kernel/PerformanceEventBuffer.cpp
@@ -39,6 +39,16 @@ PerformanceEventBuffer::PerformanceEventBuffer()
 }
 
 KResult PerformanceEventBuffer::append(int type, FlatPtr arg1, FlatPtr arg2)
+{
+ FlatPtr ebp;
+ asm volatile("movl %%ebp, %%eax"
+ : "=a"(ebp));
+ auto current_thread = Thread::current();
+ auto eip = current_thread->get_register_dump_from_stack().eip;
+ return append_with_eip_and_ebp(eip, ebp, type, arg1, arg2);
+}
+
+KResult PerformanceEventBuffer::append_with_eip_and_ebp(u32 eip, u32 ebp, int type, FlatPtr arg1, FlatPtr arg2)
 {
  if (count() >= capacity())
  return KResult(-ENOBUFS);
@@ -60,11 +70,7 @@ KResult PerformanceEventBuffer::append(int type, FlatPtr arg1, FlatPtr arg2)
  return KResult(-EINVAL);
  }
 
- FlatPtr ebp;
- asm volatile("movl %%ebp, %%eax"
- : "=a"(ebp));
  auto current_thread = Thread::current();
- auto eip = current_thread->get_register_dump_from_stack().eip;
  Vector<FlatPtr> backtrace;
  {
  SmapDisabler disabler;

diff --git a/Kernel/PerformanceEventBuffer.h b/Kernel/PerformanceEventBuffer.h
@@ -61,6 +61,7 @@ class PerformanceEventBuffer {
  PerformanceEventBuffer();
 
  KResult append(int type, FlatPtr arg1, FlatPtr arg2);
+ KResult append_with_eip_and_ebp(u32 eip, u32 ebp, int type, FlatPtr arg1, FlatPtr arg2);
 
  void clear()
  {

diff --git a/Kernel/Scheduler.cpp b/Kernel/Scheduler.cpp
@@ -495,7 +495,7 @@ void Scheduler::timer_tick(const RegisterState& regs)
  if (current_thread->process().is_profiling()) {
  ASSERT(current_thread->process().perf_events());
  auto& perf_events = *current_thread->process().perf_events();
- [[maybe_unused]] auto rc = perf_events.append(PERF_EVENT_SAMPLE, 0, 0);
+ [[maybe_unused]] auto rc = perf_events.append_with_eip_and_ebp(regs.eip, regs.ebp, PERF_EVENT_SAMPLE, 0, 0);
  }
 
  if (current_thread->tick((regs.cs & 3) == 0))