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HAProxy - Load balancer
598cf3f22e
thread_isolate() and thread_isolate_full() were relying on a set of thread masks for all threads in different states (rdv, harmless, idle). This cannot work anymore when the number of threads increases beyond LONGBITS so we need to change the mechanism. What is done here is to have a counter of requesters and the number of the current isolated thread. Threads which want to isolate themselves increment the request counter and wait for all threads to be marked harmless (or idle) by scanning all groups and watching the respective masks. This is possible because threads cannot escape once they discover this counter, unless they also want to isolate and possibly pass first. Once all threads are harmless, the requesting thread tries to self-assign the isolated thread number, and if it fails it loops back to checking all threads. If it wins it's guaranted to be alone, and can drop its harmless bit, so that other competing threads go back to the loop waiting for all threads to be harmless. The benefit of proceeding this way is that there's very little write contention on the thread number (none during work), hence no cache line moves between caches, thus frozen threads do not slow down the isolated one. Once it's done, the isolated thread resets the thread number (hence lets another thread take the place) and decrements the requester count, thus possibly releasing all harmless threads. With this change there's no more need for any global mask to synchronize any thread, and we only need to loop over a number of groups to check 64 threads at a time per iteration. As such, tinfo's threads_want_rdv could be dropped. This was tested with 64 threads spread into 2 groups, running 64 tasks (from the debug dev command), 20 "show sess" (thread_isolate()), 20 "add server blah/blah" (thread_isolate()), and 20 "del server blah/blah" (thread_isolate_full()). The load remained very low (limited by external socat forks) and no stuck nor starved thread was found. |
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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)