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When testing strong queue contention on a 48-thread machine, some crashes would frequently happen due to process_srv_queue() never leaving and processing pending requests forever. A dump showed more than 500000 loops at once. The problem is that other threads find it working so they don't do anything and are free to process their pending requests. Because of this, the dequeuing thread can be kept busy forever and does not process its own requests anymore (fortunately the watchdog stops it). This patch adds a limit to the number of rounds, it limits it to maxpollevents, which is reasonable because it's also an indicator of latency and batches size. However there's a catch. If all requests are finished when the thread ends the loop, there might not be enough anymore to restart processing the queue. Thus we tolerate to re-enter the loop to process one request at a time when it doesn't have any anymore. This way we're leaving more room for another thread to take on this task, and we're sure to eventually end this loop. Doing this has also improved the overall dequeuing performance by ~20% in highly contended situations with 48 threads. It should be backported at least to 2.4, maybe even 2.2 since issues were faced in the past on machines having many cores. |
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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)