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path: root/erts/include/erl_native_features_config.h.in
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2014-01-28initial support for dirty schedulers and dirty NIFsSteve Vinoski
Add initial support for dirty schedulers. There are two types of dirty schedulers: CPU schedulers and I/O schedulers. By default, there are as many dirty CPU schedulers as there are normal schedulers and as many dirty CPU schedulers online as normal schedulers online. There are 10 dirty I/O schedulers (similar to the choice of 10 as the default for async threads). By default, dirty schedulers are disabled and conditionally compiled out. To enable them, you must pass --enable-dirty-schedulers to the top-level configure script when building Erlang/OTP. Current dirty scheduler support requires the emulator to be built with SMP support. This restriction will be lifted in the future. You can specify the number of dirty schedulers with the command-line options +SDcpu (for dirty CPU schedulers) and +SDio (for dirty I/O schedulers). The +SDcpu option is similar to the +S option in that it takes two numbers separated by a colon: C1:C2, where C1 specifies the number of dirty schedulers available and C2 specifies the number of dirty schedulers online. The +SDPcpu option allows numbers of dirty CPU schedulers available and dirty CPU schedulers online to be specified as percentages, similar to the existing +SP option for normal schedulers. The number of dirty CPU schedulers created and dirty CPU schedulers online may not exceed the number of normal schedulers created and normal schedulers online, respectively. The +SDio option takes only a single number specifying the number of dirty I/O schedulers available and online. There is no support yet for programmatically changing at run time the number of dirty CPU schedulers online via erlang:system_flag/2. Also, changing the number of normal schedulers online via erlang:system_flag(schedulers_online, NewSchedulersOnline) should ensure that there are no more dirty CPU schedulers than normal schedulers, but this is not yet implemented. You can retrieve the number of dirty schedulers by passing dirty_cpu_schedulers, dirty_cpu_schedulers_online, or dirty_io_schedulers to erlang:system_info/1. Currently only NIFs are able to access dirty scheduler functionality. Neither drivers nor BIFs currently support dirty schedulers. This restriction will be addressed in the future. If dirty scheduler support is present in the runtime, the initial status line Erlang prints before presenting its interactive prompt will include the indicator "[ds:C1:C2:I]" where "ds" indicates "dirty schedulers", "C1" indicates the number of dirty CPU schedulers available, "C2" indicates the number of dirty CPU schedulers online, and "I" indicates the number of dirty I/O schedulers. Document The dirty NIF API in the erl_nif man page. The API closely follows Rickard Green's presentation slides from his talk "Future Extensions to the Native Interface", presented at the 2011 Erlang Factory held in the San Francisco Bay Area. Rickard's slides are available online at http://bit.ly/1m34UHB . Document the new erl command-line options, the additions to erlang:system_info/1, and also add the erlang:system_flag/2 dirty scheduler documentation even though it's not yet implemented. To determine whether the dirty NIF API is available, native code can check to see whether the C preprocessor macro ERL_NIF_DIRTY_SCHEDULER_SUPPORT is defined. To check if dirty schedulers are available at run time, native code can call the boolean enif_have_dirty_schedulers() function, and Erlang code can call erlang:system_info(dirty_cpu_schedulers), which raises badarg if no dirty scheduler support is available. Add a simple dirty NIF test to the emulator NIF suite.