From 6f63f5cecc27c7f145e319c20aec2ba51046dfc3 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Sun, 7 Apr 2013 20:49:54 +0200 Subject: [PATCH] Change from level-triggered to edge-triggered epoll mode. More than halves CPU usage. --- server.cpp | 103 ++++++++++++++++++++++++++++++++--------------------- server.h | 15 +++++++- 2 files changed, 76 insertions(+), 42 deletions(-) diff --git a/server.cpp b/server.cpp index 3e639cf..c8d6889 100644 --- a/server.cpp +++ b/server.cpp @@ -216,11 +216,11 @@ void Server::add_client_from_serialized(const ClientProto &client) // Start listening on data from this socket. epoll_event ev; if (client.state() == Client::READING_REQUEST) { - ev.events = EPOLLIN | EPOLLRDHUP; + ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP; } else { // If we don't have more data for this client, we'll be putting it into // the sleeping array again soon. - ev.events = EPOLLOUT | EPOLLRDHUP; + ev.events = EPOLLOUT | EPOLLET | EPOLLRDHUP; } ev.data.u64 = 0; // Keep Valgrind happy. ev.data.fd = client.sock(); @@ -282,26 +282,32 @@ void Server::add_data(const string &stream_id, const char *data, size_t bytes) memcpy(stream->data + pos, data, bytes); wake_up_all_clients(); } - + +// See the .h file for postconditions after this function. void Server::process_client(Client *client) { switch (client->state) { case Client::READING_REQUEST: { +read_request_again: // Try to read more of the request. char buf[1024]; int ret; do { ret = read(client->sock, buf, sizeof(buf)); } while (ret == -1 && errno == EINTR); + + if (ret == -1 && errno == EAGAIN) { + // No more data right now. Nothing to do. + // This is postcondition #2. + return; + } if (ret == -1) { perror("read"); close_client(client); return; } if (ret == 0) { - // No data? This really means that we were triggered for something else than - // POLLIN (which suggests a logic error in epoll). - fprintf(stderr, "WARNING: fd %d returned unexpectedly 0 bytes!\n", client->sock); + // OK, the socket is closed. close_client(client); return; } @@ -324,7 +330,8 @@ void Server::process_client(Client *client) "\r\n\r\n", 4)); if (ptr == NULL) { // OK, we don't have the entire header yet. Fine; we'll get it later. - return; + // See if there's more data for us. + goto read_request_again; } if (ptr != client->request.data() + client->request.size() - 4) { @@ -339,17 +346,31 @@ void Server::process_client(Client *client) } else { construct_error(client, error_code); } - break; + + // We've changed states, so fall through. + assert(client->state == Client::SENDING_ERROR || + client->state == Client::SENDING_HEADER); } case Client::SENDING_ERROR: case Client::SENDING_HEADER: { +sending_header_or_error_again: int ret; do { ret = write(client->sock, client->header_or_error.data() + client->header_or_error_bytes_sent, client->header_or_error.size() - client->header_or_error_bytes_sent); } while (ret == -1 && errno == EINTR); + + if (ret == -1 && errno == EAGAIN) { + // We're out of socket space, so now we're at the “low edge” of epoll's + // edge triggering. epoll will tell us when there is more room, so for now, + // just return. + // This is postcondition #4. + return; + } + if (ret == -1) { + // Error! Postcondition #1. perror("write"); close_client(client); return; @@ -359,22 +380,27 @@ void Server::process_client(Client *client) assert(client->header_or_error_bytes_sent <= client->header_or_error.size()); if (client->header_or_error_bytes_sent < client->header_or_error.size()) { - // We haven't sent all yet. Fine; we'll do that later. - return; + // We haven't sent all yet. Fine; go another round. + goto sending_header_or_error_again; } // We're done sending the header or error! Clear it to release some memory. client->header_or_error.clear(); if (client->state == Client::SENDING_ERROR) { + // We're done sending the error, so now close. + // This is postcondition #1. close_client(client); - } else { - // Start sending from the end. In other words, we won't send any of the backlog, - // but we'll start sending immediately as we get data. - client->state = Client::SENDING_DATA; - client->bytes_sent = find_stream(client->stream_id)->data_size; + return; } - break; + + // Start sending from the end. In other words, we won't send any of the backlog, + // but we'll start sending immediately as we get data. + // This is postcondition #3. + client->state = Client::SENDING_DATA; + client->bytes_sent = find_stream(client->stream_id)->data_size; + sleeping_clients.push_back(client); + return; } case Client::SENDING_DATA: { // See if there's some data we've lost. Ideally, we should drop to a block boundary, @@ -411,7 +437,14 @@ void Server::process_client(Client *client) bytes_to_send); } while (ret == -1 && errno == EINTR); } + if (ret == -1 && errno == EAGAIN) { + // We're out of socket space, so return; epoll will wake us up + // when there is more room. + // This is postcondition #4. + return; + } if (ret == -1) { + // Error, close; postcondition #1. perror("write/writev"); close_client(client); return; @@ -420,7 +453,11 @@ void Server::process_client(Client *client) if (client->bytes_sent == stream.data_size) { // We don't have any more data for this client, so put it to sleep. + // This is postcondition #3. put_client_to_sleep(client); + } else { + // XXX: Do we need to go another round here to explicitly + // get the EAGAIN? } break; } @@ -462,7 +499,7 @@ void Server::construct_header(Client *client) client->state = Client::SENDING_HEADER; epoll_event ev; - ev.events = EPOLLOUT | EPOLLRDHUP; + ev.events = EPOLLOUT | EPOLLET | EPOLLRDHUP; ev.data.u64 = 0; // Keep Valgrind happy. ev.data.fd = client->sock; @@ -483,7 +520,7 @@ void Server::construct_error(Client *client, int error_code) client->state = Client::SENDING_ERROR; epoll_event ev; - ev.events = EPOLLOUT | EPOLLRDHUP; + ev.events = EPOLLOUT | EPOLLET | EPOLLRDHUP; ev.data.u64 = 0; // Keep Valgrind happy. ev.data.fd = client->sock; @@ -501,8 +538,8 @@ void Server::close_client(Client *client) } // This client could be sleeping, so we'll need to fix that. (Argh, O(n).) - vector::iterator new_end = - remove(sleeping_clients.begin(), sleeping_clients.end(), client->sock); + vector::iterator new_end = + remove(sleeping_clients.begin(), sleeping_clients.end(), client); sleeping_clients.erase(new_end, sleeping_clients.end()); // Bye-bye! @@ -520,32 +557,16 @@ void Server::close_client(Client *client) void Server::put_client_to_sleep(Client *client) { - epoll_event ev; - ev.events = EPOLLRDHUP; - ev.data.u64 = 0; // Keep Valgrind happy. - ev.data.fd = client->sock; - - if (epoll_ctl(epoll_fd, EPOLL_CTL_MOD, client->sock, &ev) == -1) { - perror("epoll_ctl(EPOLL_CTL_MOD)"); - exit(1); - } - - sleeping_clients.push_back(client->sock); + sleeping_clients.push_back(client); } void Server::wake_up_all_clients() { - for (unsigned i = 0; i < sleeping_clients.size(); ++i) { - epoll_event ev; - ev.events = EPOLLOUT | EPOLLRDHUP; - ev.data.u64 = 0; // Keep Valgrind happy. - ev.data.fd = sleeping_clients[i]; - if (epoll_ctl(epoll_fd, EPOLL_CTL_MOD, sleeping_clients[i], &ev) == -1) { - perror("epoll_ctl(EPOLL_CTL_MOD)"); - exit(1); - } + vector to_process; + swap(sleeping_clients, to_process); + for (unsigned i = 0; i < to_process.size(); ++i) { + process_client(to_process[i]); } - sleeping_clients.clear(); } Stream *Server::find_stream(const string &stream_id) diff --git a/server.h b/server.h index cc1b78d..24e2fcb 100644 --- a/server.h +++ b/server.h @@ -120,7 +120,7 @@ private: // Clients that are in SENDING_DATA, but that we don't listen on, // because we currently don't have any data for them. // See put_client_to_sleep() and wake_up_all_clients(). - std::vector sleeping_clients; + std::vector sleeping_clients; // Recover the this pointer, and call do_work(). static void *do_work_thunk(void *arg); @@ -128,6 +128,19 @@ private: // The actual worker thread. void do_work(); + // Process a client; read and write data as far as we can. + // After this call, one of these four is true: + // + // 1. The socket is closed, and the client deleted. + // 2. We are still waiting for more data from the client. + // 3. We've sent all the data we have to the client, + // and put it in . + // 4. The socket buffer is full (which means we still have + // data outstanding). + // + // For #2, we listen for EPOLLIN events. For #3 and #4, we listen + // for EPOLLOUT in edge-triggered mode; it will never fire for #3, + // but it's cheaper than taking it in and out all the time. void process_client(Client *client); // Close a given client socket, and clean up after it. -- 2.39.2