Willy Tarreau 5be2f35231 MAJOR: polling: centralize calls to I/O callbacks ... In order for HTTP/2 not to eat too much memory, we'll have to support on-the-fly buffer allocation, since most streams will have an empty request buffer at some point. Supporting allocation on the fly means being able to sleep inside I/O callbacks if a buffer is not available. Till now, the I/O callbacks were called from two locations : - when processing the cached events - when processing the polled events from the poller This change cleans up the design a bit further than what was started in 1.5. It now ensures that we never call any iocb from the poller itself and that instead, events learned by the poller are put into the cache. The benefit is important in terms of stability : we don't have to care anymore about the risk that new events are added into the poller while processing its events, and we're certain that updates are processed at a single location. To achieve this, we now modify all the fd_* functions so that instead of creating updates, they add/remove the fd to/from the cache depending on its state, and only create an update when the polling status reaches a state where it will have to change. Since the pollers make use of these functions to notify readiness (using fd_may_recv/fd_may_send), the cache is always up to date with the poller. Creating updates only when the polling status needs to change saves a significant amount of work for the pollers : a benchmark showed that on a typical TCP proxy test, the amount of updates per connection dropped from 11 to 1 on average. This also means that the update list is smaller and has more chances of not thrashing too many CPU cache lines. The first observed benefit is a net 2% performance gain on the connection rate. A second benefit is that when a connection is accepted, it's only when we're processing the cache, and the recv event is automatically added into the cache *after* the current one, resulting in this event to be processed immediately during the same loop. Previously we used to have a second run over the updates to detect if new events were added to catch them before waking up tasks. The next gain will be offered by the next steps on this subject consisting in implementing an I/O queue containing all cached events ordered by priority just like the run queue, and to be able to leave some events pending there as long as needed. That will allow us *not* to perform some FD processing if it's not the proper time for this (typically keep waiting for a buffer to be allocated if none is available for an recv()). And by only processing a small bunch of them, we'll allow priorities to take place even at the I/O level. As a result of this change, functions fd_alloc_or_release_cache_entry() and fd_process_polled_events() have disappeared, and the code dedicated to checking for new fd events after the callback during the poll() loop was removed as well. Despite the patch looking large, it's mostly a change of what function is falled upon fd_*() and almost nothing was added.		2014-11-21 20:37:32 +01:00
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common	MAJOR: namespace: add Linux network namespace support	2014-11-21 07:51:57 +01:00
import	[MAJOR] replace ultree with ebtree in wait-queues	2008-06-24 08:17:16 +02:00
proto	MAJOR: polling: centralize calls to I/O callbacks	2014-11-21 20:37:32 +01:00
types	MAJOR: namespace: add Linux network namespace support	2014-11-21 07:51:57 +01:00