Asynchronous buffered read operations

Posted Mar 20, 2015 15:05 UTC (Fri) by Cyberax (✭ supporter ✭, #52523)
In reply to: Asynchronous buffered read operations by mtanski
Parent article: Asynchronous buffered read operations

The problem here is in multiplexing. It's extremely common to have a loop that reads data from a disk and puts it into a network socket.

And there's no real way to do it asynchronously in one thread - poll/epoll don't work for disk IO and aio doesn't work for sockets.

Asynchronous buffered read operations

Posted Mar 20, 2015 15:17 UTC (Fri) by mtanski (guest, #56423) [Link] (1 responses)

You have two options:

1. io_submit(), eventfd(), poll() the eventfd
Any requests you submit via io_submit can have an optional notification via eventfd. You have to set that in the struct iocb. The downside is that you're limited to O_DIRECT and it can still block in some cases.

2. Build yourself a threadpool for handling IO.
This is kind of what everybody does today who doesn't do O_DIRECT. It still issues like introducing latency (synchronization, slow requests). This is what this RWF_NONBLOCK addresses it lets you try doing a "fast read" from your network thread, so you can skip the threadpool if the data is there (because of kernel readahead or because it's hot data).