From 71a59d20e068dae48f37f4085fe5783667784cfb Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 21 Sep 2019 12:13:24 -0700
Subject: [PATCH] ircd::prof: Add a scope_cycles utility device.

---
 include/ircd/prof/prof.h         |  1 +
 include/ircd/prof/scope_cycles.h | 63 ++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 include/ircd/prof/scope_cycles.h

diff --git a/include/ircd/prof/prof.h b/include/ircd/prof/prof.h
index 7a38e9d91..a1c577460 100644
--- a/include/ircd/prof/prof.h
+++ b/include/ircd/prof/prof.h
@@ -35,6 +35,7 @@ namespace ircd::prof
 #include "x86.h"
 #include "vg.h"
 #include "type.h"
+#include "scope_cycles.h"
 #include "syscall_timer.h"
 #include "instructions.h"
 #include "resource.h"
diff --git a/include/ircd/prof/scope_cycles.h b/include/ircd/prof/scope_cycles.h
new file mode 100644
index 000000000..472dc2a7a
--- /dev/null
+++ b/include/ircd/prof/scope_cycles.h
@@ -0,0 +1,63 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#pragma once
+#define HAVE_IRCD_PROF_SCOPE_CYCLES_H
+
+namespace ircd::prof
+{
+	struct scope_cycles;
+}
+
+/// Count the reference cycles for a scope using the lifetime of this object.
+/// The result is stored in `result`. Note that `result` is also used while
+/// this object is operating.
+struct ircd::prof::scope_cycles
+{
+	uint64_t &result;
+
+	scope_cycles(uint64_t &result) noexcept;
+	~scope_cycles() noexcept;
+};
+
+extern inline
+__attribute__((flatten, always_inline, gnu_inline, artificial))
+ircd::prof::scope_cycles::scope_cycles(uint64_t &result)
+noexcept
+:result{result}
+{
+	#if defined(__x86_64__) || defined(__i386__)
+	asm volatile ("mfence");
+	asm volatile ("lfence");
+	#endif
+
+	result = cycles();
+
+	#if defined(__x86_64__) || defined(__i386__)
+	asm volatile ("lfence");
+	#endif
+}
+
+extern inline
+__attribute__((flatten, always_inline, gnu_inline, artificial))
+ircd::prof::scope_cycles::~scope_cycles()
+noexcept
+{
+	#if defined(__x86_64__) || defined(__i386__)
+	asm volatile ("mfence");
+	asm volatile ("lfence");
+	#endif
+
+	result = cycles() - result;
+
+	#if defined(__x86_64__) || defined(__i386__)
+	asm volatile ("lfence");
+	#endif
+}