mirror of
https://github.com/matrix-construct/construct
synced 2024-12-30 17:34:04 +01:00
122 lines
3.6 KiB
C++
122 lines
3.6 KiB
C++
// The Construct
|
|
//
|
|
// Copyright (C) The Construct Developers, Authors & Contributors
|
|
// Copyright (C) 2016-2020 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_IOS_EPOLL_H
|
|
|
|
// Forward declarations because sys/epoll.h is not included here
|
|
extern "C"
|
|
{
|
|
struct epoll_event;
|
|
}
|
|
|
|
// This interface provides special workarounds and optimizations for the epoll
|
|
// reactor in boost::asio on linux systems. It has to be used voluntarily by
|
|
// the embedder of libircd, who can hook calls to epoll_wait(2), and forward
|
|
// those calls to this interface. Our implementation then makes the syscall.
|
|
namespace ircd::ios
|
|
{
|
|
using epoll_wait_proto = int (int, struct ::epoll_event *, int, int);
|
|
|
|
template<epoll_wait_proto *>
|
|
int epoll_wait(int, struct ::epoll_event *, int, int) noexcept;
|
|
}
|
|
|
|
/// This reduces the number of syscalls to epoll_wait(2), which tend to occur
|
|
/// at the start of every epoch except in a minority of cases. These syscalls
|
|
/// produce no ready events 99% of the time.
|
|
///
|
|
/// boost::asio tends to call epoll_wait(2) with timeout=0 (non-blocking) when
|
|
/// it has more work queued that it will execute. If there's nothing queued it
|
|
/// will set a timeout. We don't need to collect epoll events so aggressively.
|
|
/// It's incumbent upon us to not spam thousands of non-blocking syscalls which
|
|
/// yield no results, especially when it negates the efficiency of ircd::ctx's
|
|
/// fast userspace context switching. We trade some responsiveness for things
|
|
/// like asio::signal_set but gain overall performance which now has actual
|
|
/// impact in the post-meltdown/spectre virtualized reality.
|
|
///
|
|
template<ircd::ios::epoll_wait_proto *_real_epoll_wait>
|
|
[[using gnu: hot, always_inline]]
|
|
inline int
|
|
ircd::ios::epoll_wait(int _epfd,
|
|
struct ::epoll_event *const _events,
|
|
int _maxevents,
|
|
int _timeout)
|
|
noexcept
|
|
{
|
|
// Call elision tick counter.
|
|
thread_local uint64_t tick;
|
|
|
|
// Configured frequency to allow the call.
|
|
const uint64_t freq
|
|
{
|
|
empt::freq
|
|
};
|
|
|
|
const bool skip
|
|
{
|
|
!freq || (tick < freq)
|
|
};
|
|
|
|
const bool peek
|
|
{
|
|
_timeout == 0
|
|
};
|
|
|
|
// Always allow blocking calls; only allow non-blocking calls which
|
|
// satisfy our conditions.
|
|
const bool call
|
|
{
|
|
!peek || !skip
|
|
};
|
|
|
|
// Modify tick counter prior to call, while we have the line.
|
|
tick -= boolmask<decltype(tick)>(call) & tick;
|
|
tick += boolmask<decltype(tick)>(!call) & 0x01;
|
|
|
|
const int ret
|
|
{
|
|
call?
|
|
_real_epoll_wait(_epfd, _events, _maxevents, _timeout): 0
|
|
};
|
|
|
|
// Update stats
|
|
empt::peek += peek;
|
|
empt::skip += !call;
|
|
empt::call += call;
|
|
empt::none += call && ret == 0;
|
|
empt::result += ret & boolmask<uint>(ret >= 0);
|
|
empt::load_low += ret >= _maxevents / 8;
|
|
empt::load_med += ret >= _maxevents / 4;
|
|
empt::load_high += ret >= _maxevents / 2;
|
|
empt::load_stall += ret >= _maxevents / 1;
|
|
|
|
if constexpr(profile::logging) if(call)
|
|
log::logf
|
|
{
|
|
log, ircd::log::DEBUG,
|
|
"EPOLL %5d tick:%lu peek:%lu skip:%lu call:%lu none:%lu result:%lu low:%lu med:%lu high:%lu stall:%lu",
|
|
ret,
|
|
tick,
|
|
uint64_t(empt::peek),
|
|
uint64_t(empt::skip),
|
|
uint64_t(empt::call),
|
|
uint64_t(empt::none),
|
|
uint64_t(empt::result),
|
|
uint64_t(empt::load_low),
|
|
uint64_t(empt::load_med),
|
|
uint64_t(empt::load_high),
|
|
uint64_t(empt::load_stall),
|
|
};
|
|
|
|
assert(call || ret == 0);
|
|
assert(ret <= _maxevents);
|
|
return ret;
|
|
}
|