![]() Interactive tasks should avoid performing high latency operations, and if they are long duration tasks, should yield frequently. To address this, you can specify that a task is interactive when you it: using :interactive f() When a program's threads are busy with many tasks to run, tasks may experience delays which may negatively affect the responsiveness and interactivity of the program. For more fine grained control over worker threads use addprocs and pass -t/ -threads as exeflags. For example, julia -p2 -t2 spawns 1 main process with 2 worker processes, and all three processes have 2 threads enabled. The number of threads specified with -t/ -threads is propagated to worker processes that are spawned using the -p/ -procs or -machine-file command line options. Instrumenting Julia with DTrace, and bpftrace.Reporting and analyzing crashes (segfaults).Static analyzer annotations for GC correctness in C code.Proper maintenance and care of multi-threading locks.printf() and stdio in the Julia runtime.Talking to the compiler (the :meta mechanism).High-level Overview of the Native-Code Generation Process.Noteworthy Differences from other Languages.Multi-processing and Distributed Computing.Side effects and mutable function arguments.Mathematical Operations and Elementary Functions.What is the best solution will clear depend on the amount of work being done in the dgemm operation compared to the synchronization overhead for fork/join, which in mostly dominated by the thread count and the internal implementation. The additional joins and forks will also introduce some overhead, but it may be better than the over-subscription of the initial solution with the single construct or solution 1. The downside is that the thread has to wake up from this deeper sleep state, which will increase the latency compared to the spin-wait.įor solution 2, the threads are kept in their spin-wait loop and are very likely actively waiting when the dgemm call enters its parallel region. exeĢ) Modify the code to split the parallel regions: #pragma omp parallelįor solution 1, the threads go to the sleep mode immediately and do not consume cycles. There are essentially two solutions to this problem:ġ) List item Use the code as above and in addition to the suggested environment variables also disable active waiting: $ MKL_DYNAMIC=FALSE MKL_NUM_THREADS=8 OMP_NUM_THREADS=8 OMP_NESTED=TRUE OMP_WAIT_MODE=passive. ![]() What will happen is that even if the dgemm call creates additional threads inside MKL, the outer-level threads will still be actively waiting for the end of the single construct and thus dgemm will run with reduced performance. Instead, the threads will enter a spin-wait loop and continue to consume processor cycles while they are waiting. The reason is that most OpenMP implementations do not shutdown the threads when they reach a barrier or don't have work to do. The above answer is correct from a function perspective, but will not give best results from a performance perspective. While this post is a bit dated, I would still like to give some useful insights for it. ![]() Though I would prefer to use environment variables instead. ![]() You could also set the parameters with the appropriate calls: mkl_set_dynamic(0) Therefore I would assume that your case is the former.Īnd run with: $ MKL_DYNAMIC=FALSE MKL_NUM_THREADS=8 OMP_NUM_THREADS=8 OMP_NESTED=TRUE. If each thread processes its own private data, then you don't need any synchronisation constructs, but using multithreaded MKL won't give you any benefit too. If the data to be processes with dgemm_ is shared, then you have to invoke the latter from within a single construct. Once that is sorted out, you should enable nested parallelism by setting OMP_NESTED to TRUE and disable MKL's detection of nested parallelism by setting MKL_DYNAMIC to FALSE. The reason for that restriction is that MKL uses Intel's OpenMP runtime and that different OMP runtimes do not play well with each other. It is supported by MKL, but it only works if your executable is built using the Intel C/C++ compiler. ![]()
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