Limiting the number of threads created

[hkleynhans]

We have a requirement to manually limit the maximum number of worker-threads created by oneTBB. Looking through it code it appears that at the moment the number of workers is determined by the number of cores, multiplied by a factor with a minimum number of 256.

This requirement is largely based on working around a bug in dealing with many task handles in a version of the Linux kernel we cannot upgrade at the moment.

Is there a recommended way to place a hard limit on the number of threads created?

It would be great to understand if:

• this is a feature other people need; or if we need to patch our own copy of TBB?
• it is sufficient to just patch the AvailableHwConcurrency code-path and workers_hard_limit calculation?
• is the guarantee that there are at least 256 workers relied upon anywhere? Will anything break if this is decreased?

[pavelkumbrasev]

Hi @hkleynhans, you can start with global_control with max_allowed_parallelism you can limit amount of threads available for oneTBB (you can lower it or increase). It will globally affect the target application. I also can suggest to do it together with limiting task_arena concurrency it will help insure proper thread distribution across the task_arenas. There is an example.

[hkleynhans]

Thanks for the info @pavelkumbrasev - let me test and verify that with our environment

[JhaShweta1]

Please reopen this if you are still facing this issue.