Add config option to leverage all cores for sabre (backport #12780) #12841
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* Add config option to leverage all cores for sabre By default when running sabre in parallel we use a fixed number of threads (depending on optimization level). This was a tradeoff made for having deterministic results across multiple systems with a fixed seed set. However when running qiskit on systems with a lot of CPUs available we're leaving potential performance on the table by not using all the available cores. This new flag lets users opt-in to running sabre with n trials for n CPUs to potentially get better output results from the transpiler, with minimal to no runtime overhead, at the cost of the results not necessarily being reproducible when run on a different computer. * Apply suggestions from code review Co-authored-by: Elena Peña Tapia <57907331+ElePT@users.noreply.github.com> * Rework logic to use the default if larger than CPU_COUNT This commit refactors the logic added in the previous commit to a single helper function. This reduces the code duplication and makes it easier to work with. While doing this the logic has been updated so that when the flag is set and the default number of trials is larger than the CPU_COUNT we use the default. This means the logic when the flag is set is to run `max(default_trials, CPU_COUNT)` which should better match user expectations around the flag. --------- Co-authored-by: Elena Peña Tapia <57907331+ElePT@users.noreply.github.com> (cherry picked from commit f8ac2ad)
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Jul 29, 2024
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Summary
By default when running sabre in parallel we use a fixed number of threads (depending on optimization level). This was a tradeoff made for having deterministic results across multiple systems with a fixed seed set. However when running qiskit on systems with a lot of CPUs available we're leaving potential performance on the table by not using all the available cores. This new flag lets users opt-in to running sabre with n trials for n CPUs to potentially get better output results from the transpiler, with minimal to no runtime overhead, at the cost of the results not necessarily being reproducible when run on a different computer.
Details and comments
This is an automatic backport of pull request #12780 done by Mergify.