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Kernel: Implement a simple process time profiler

The kernel now supports basic profiling of all the threads in a process
by calling profiling_enable(pid_t). You finish the profiling by calling
profiling_disable(pid_t).

This all works by recording thread stacks when the timer interrupt
fires and the current thread is in a process being profiled.
Note that symbolication is deferred until profiling_disable() to avoid
adding more noise than necessary to the profile.

A simple "/bin/profile" command is included here that can be used to
start/stop profiling like so:

    $ profile 10 on
    ... wait ...
    $ profile 10 off

After a profile has been recorded, it can be fetched in /proc/profile

There are various limits (or "bugs") on this mechanism at the moment:

- Only one process can be profiled at a time.
- We allocate 8MB for the samples, if you use more space, things will
  not work, and probably break a bit.
- Things will probably fall apart if the profiled process dies during
  profiling, or while extracing /proc/profile
This commit is contained in:
Andreas Kling 2019-12-11 20:36:56 +01:00
parent adb1870628
commit b32e961a84
13 changed files with 388 additions and 135 deletions

View file

@ -23,6 +23,7 @@
#include <Kernel/Net/TCPSocket.h>
#include <Kernel/Net/UDPSocket.h>
#include <Kernel/PCI.h>
#include <Kernel/Profiling.h>
#include <Kernel/VM/MemoryManager.h>
#include <Kernel/VM/PurgeableVMObject.h>
#include <LibC/errno_numbers.h>
@ -55,6 +56,7 @@ enum ProcFileType {
FI_Root_uptime,
FI_Root_cmdline,
FI_Root_modules,
FI_Root_profile,
FI_Root_self, // symlink
FI_Root_sys, // directory
FI_Root_net, // directory
@ -353,6 +355,31 @@ Optional<KBuffer> procfs$modules(InodeIdentifier)
return builder.build();
}
Optional<KBuffer> procfs$profile(InodeIdentifier)
{
InterruptDisabler disabler;
KBufferBuilder builder;
JsonArraySerializer array(builder);
Profiling::for_each_sample([&](auto& sample) {
auto object = array.add_object();
object.add("pid", sample.pid);
object.add("tid", sample.tid);
object.add("timestamp", sample.timestamp);
auto sample_array = object.add_array("samples");
for (size_t i = 0; i < Profiling::max_stack_frame_count; ++i) {
if (sample.frames[i] == 0)
break;
auto frame_object = sample_array.add_object();
frame_object.add("address", JsonValue((u32)sample.frames[i]));
frame_object.add("symbol", sample.symbolicated_frames[i]);
frame_object.finish();
}
sample_array.finish();
});
array.finish();
return builder.build();
}
Optional<KBuffer> procfs$net_adapters(InodeIdentifier)
{
KBufferBuilder builder;
@ -1333,6 +1360,7 @@ ProcFS::ProcFS()
m_entries[FI_Root_uptime] = { "uptime", FI_Root_uptime, procfs$uptime };
m_entries[FI_Root_cmdline] = { "cmdline", FI_Root_cmdline, procfs$cmdline };
m_entries[FI_Root_modules] = { "modules", FI_Root_modules, procfs$modules };
m_entries[FI_Root_profile] = { "profile", FI_Root_profile, procfs$profile };
m_entries[FI_Root_sys] = { "sys", FI_Root_sys };
m_entries[FI_Root_net] = { "net", FI_Root_net };