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construct/include/ircd/prof/syscall_timer.h
Jason Volk fefaaca2c2 ircd::prof: Split header into directory.
ircd::prof: Split linux/perf_event specific to unit.
2019-07-31 19:43:09 -07:00

55 lines
1.6 KiB
C++

// 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_SYSCALL_TIMER_H
namespace ircd::prof
{
struct syscall_timer;
}
/// This suite of devices is intended to figure out when a system call is
/// really slow or "blocking." The original use-case is for io_submit() in
/// fs::aio.
///
/// The sample is conducted with times(2) which is itself a system call
/// though reasonably fast, and the result has poor resolution meaning
/// the result of at() is generally 0 unless the system call was very slow.
///
/// It is started on construction. The user must later call sample()
/// which returns the value of at() as well.
struct ircd::prof::syscall_timer
{
struct high_resolution;
uint64_t started, stopped;
public:
uint64_t at() const;
uint64_t sample();
syscall_timer() noexcept;
};
/// This is a higher resolution alternative. The sample may be conducted
/// with getrusage() or perf events; the exact method is TBD and may be
/// expensive/intrusive. This device should be used temporarily by developers
/// and not left in place in committed code.
struct ircd::prof::syscall_timer::high_resolution
{
uint64_t started, stopped;
public:
uint64_t at() const;
uint64_t sample();
high_resolution() noexcept;
};