Martin Sustrik <sustrik@xxxxxxxxxx> wrote: > On 08/02/13 23:21, Eric Wong wrote: > >Martin Sustrik<sustrik@xxxxxxxxxx> wrote: > >>To address the question, I've written down detailed description of > >>the challenges of the network protocol development in user space and > >>how the proposed feature addresses the problems. > >> > >>It can be found here: http://www.250bpm.com/blog:16 > > > >Using one eventfd per userspace socket still seems a bit wasteful. > > Wasteful in what sense? Occupying a slot in file descriptor table? > That's the price for having the socket uniquely identified by the > fd. Yes. I realize eventfd is small, but I don't think eventfd is needed at all, here. Just one pipe. > >Couldn't you use a single pipe for all sockets and write the efd_mask to > >the pipe for each socket? > > > >A read from the pipe would behave like epoll_wait. > > > >You might need to use one-shot semantics; but that's probably > >the easiest thing in multithreaded apps anyways. > > Having multiple sockets represented by a single eventfd. how would > you distinguish where did individual events came from? > > struct pollfd pfd; > ... > poll (pfd, 1, -1); > if (pfd.revents & POLLIN) /* Incoming data on which socket? */ > ... No eventfd, you write just write struct to the pipe, and consume the struct to a fixed size buffer: /* trigger readiness notification for sock, * this probably needs a lock around it */ void sock_trigger(struct my_sock *sock, int events) { struct efd_mask mask; /* check if the triggeered event is something sock wants: */ events &= sock->watched_events; if (!events) return; mask.events = events; mask.ptr = sock; /* * preventing sock from being in the pipe multiple times * is probably required (or just a good idea). Which is * why I mentioned oneshot semantics are probably required. */ if (oneshot) sock->watched_events = 0; /* * This is analogous to: * list_add_tail(&epi->rdllink, &ep->rdllist); * in fs/eventpoll.c * * This may block, but that's why consumer_loop runs in different * threads. Or run some iteration of consumer_loop here if * it blocks (beware of stack depth from recursion, though) */ write(pipe_wr, &mask, sizeof(mask)); } /* in another thread (or several threads) */ void consumer_loop(int pipe_rd) { struct efd_mask mask; struct my_sock *sock; for (;;) { /* * analogous to: * epoll_wait(.., maxevents=1, ...); * * You can read several masks at once if have one thread, * but I usually use maxevents=1 (+several threads) to * distribute traffic between threads */ read(pipe_rd, &mask, sizeof(mask)); sock = mask.ptr; if (mask.events & POLLIN) sock_read(sock); else if (mask.events & POLLOUT) sock_write(sock); ... /* analogous to epoll_ctl() */ if (sock->write_buffered) sock->watched_events |= POLLOUT; if (sock->wants_more_data) sock->watched_events |= POLLIN; /* onto the next ready event */ } } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
