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Lazy epoll management

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Reduce calls to epoll_ctl() by allowing epoll events that are not
requested by the user, but have still not been satisfied by the system,
to remain installed in epoll.  We may get a spurious wakeup later, but if
we do, we remember it so that when the user does want the event, it will be
ready without a syscall.
This commit is contained in:
Avi Kivity
2014-08-18 13:04:44 +03:00
parent 784b2bf3ed
commit 96b813fbfc
2 changed files with 35 additions and 17 deletions
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48
reactor.cc
View File

@@ -21,14 +21,23 @@ reactor::~reactor() {
future<void> reactor::get_epoll_future(pollable_fd_state& pfd,
promise<void> pollable_fd_state::*pr, int event) {
auto ctl = pfd.events ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
pfd.events |= event;
if (pfd.events_known & event) {
pfd.events_known &= ~event;
promise<void> pr;
pr.set_value();
return pr.get_future();
}
pfd.events_requested |= event;
if (!(pfd.events_epoll & event)) {
auto ctl = pfd.events_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
pfd.events_epoll |= event;
::epoll_event eevt;
eevt.events = pfd.events_epoll;
eevt.data.ptr = &pfd;
int r = ::epoll_ctl(_epollfd, ctl, pfd.fd, &eevt);
assert(r == 0);
}
pfd.*pr = promise<void>();
::epoll_event eevt;
eevt.events = pfd.events;
eevt.data.ptr = &pfd;
int r = ::epoll_ctl(_epollfd, ctl, pfd.fd, &eevt);
assert(r == 0);
return (pfd.*pr).get_future();
}
@@ -41,7 +50,7 @@ future<void> reactor::writeable(pollable_fd_state& fd) {
}
void reactor::forget(pollable_fd_state& fd) {
if (fd.events) {
if (fd.events_epoll) {
::epoll_ctl(_epollfd, EPOLL_CTL_DEL, fd.fd, nullptr);
}
}
@@ -77,21 +86,28 @@ void reactor::run() {
for (int i = 0; i < nr; ++i) {
auto& evt = eevt[i];
auto pfd = reinterpret_cast<pollable_fd_state*>(evt.data.ptr);
auto events = evt.events;
auto events = evt.events & (EPOLLIN | EPOLLOUT);
std::unique_ptr<task> t_in, t_out;
if (events & EPOLLIN) {
pfd->events &= ~EPOLLIN;
pfd->events_known |= events;
auto events_to_remove = events & ~pfd->events_requested;
if (pfd->events_requested & events & EPOLLIN) {
pfd->events_requested &= ~EPOLLIN;
pfd->events_known &= ~EPOLLIN;
pfd->pollin.set_value();
pfd->pollin = promise<void>();
}
if (events & EPOLLOUT) {
pfd->events &= ~EPOLLOUT;
if (pfd->events_requested & events & EPOLLOUT) {
pfd->events_requested &= ~EPOLLOUT;
pfd->events_known &= ~EPOLLOUT;
pfd->pollout.set_value();
pfd->pollout = promise<void>();
}
evt.events = pfd->events;
auto op = evt.events ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;
::epoll_ctl(_epollfd, op, pfd->fd, &evt);
if (events_to_remove) {
pfd->events_epoll &= ~events_to_remove;
evt.events = pfd->events_epoll;
auto op = evt.events ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;
::epoll_ctl(_epollfd, op, pfd->fd, &evt);
}
}
}
}

4
reactor.hh
View File

@@ -471,7 +471,9 @@ public:
pollable_fd_state(const pollable_fd_state&) = delete;
void operator=(const pollable_fd_state&) = delete;
int fd;
int events = 0;
int events_requested = 0; // wanted by pollin/pollout promises
int events_epoll = 0; // installed in epoll
int events_known = 0; // returned from epoll
promise<void> pollin;
promise<void> pollout;
friend class reactor;