number of cores

[Zhongze_L_]

Hi,

Does anybody know how to get the number of cores in TBB?

Thanks,
Zhongze

[christian_roessel]

Hi Zhongze,

tbb::task_scheduler_init::default_num_threads() returns the number of threads that the task scheduler will use by default. Often this is equal to the number of cores, but I don't know how hyperthreading CPUs are treated.

Regards,
Christian

[Andrey_Marochko]

Each HT (or "logical") core is treated in the same way as a full core.

[AJ13]

Hi Zhongze,

If you don't mind my asking, what do you need to know the number of cores for?

AJ

[Alexey-Kukanov]

MADamarochk:

Each HT (or "logical") core is treated in the same way as a full core.

I would add that this may change in future.

[Andrey_Marochko]

To complete the picture, TBB sees only those CPUs/cores (HT or full) that are enabled by the BIOS and OS.

[Zhongze_L_]

I need that number in order to partition a graph. It doesn't make sense to partition a graph into 16 subgraphs on a dual core machine or partition a graph into 2 subgraphs on a quad-core machine.

Thanks,
Zhongze

[Andrey_Marochko]

Hi, Zhongze

As I explained in the answer to your other post, you most probably do not need to know the number of cores at all, since the degree of partitioning should depend on the amount of work necessary to process each subgraph. And if your sparse matrices are really large, then you should partition the graph in much more parts then the number of cores.

In fact partitioning into 16 (or even more) subgrapphs on dualcore machine usually makes perfect sence, as the work distribution across the subgraphs is normally very nonuniform (this is one of the problems with running MPI version of this algorithm on the grids). TBB applications running on shared memory systems can benefit from fine grained parallelism. Follow the link above for more details.