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HAProxy - Load balancer
758cb450a2
The sink lock was made to prevent event producers from passing while there were other threads trying to print a "dropped" message, in order to guarantee the absence of reordering. It has a serious impact however, which is that all threads need to take the read lock when producing a regular trace even when there's no reader. This patch takes a different approach. The drop counter is shifted left by one so that the lowest bit is used to indicate that one thread is already taking care of trying to dump the counter. Threads only read this value normally, and will only try to change it if it's non-null, in which case they'll first check if they are the first ones trying to dump it, otherwise will simply count another drop and leave. This has a large benefit. First, it will avoid the locking that causes stalls as soon as a slow reader is present. Second, it avoids any write on the fast path as long as there's no drop. And it remains very lightweight since we just need to add +2 or subtract 2*dropped in operations, while offering the guarantee that the sink_write() has succeeded before unlocking the counter. While a reader was previously limiting the traffic to 11k RPS under 4C/8T, now we reach 36k RPS vs 14k with no reader, so readers will no longer slow the traffic down and will instead even speed it up due to avoiding the contention down the chain in the ring. The locking cost dropped from ~75% to ~60% now (it's in ring_write now). |
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The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)