Number of Kernel threads

[Richard Casey]

Hi,

We're running NVBIO on K80.  For nvBowtie, in the parameter list, there does not seem to be a way to control the number of kernel threads launched on the GPU, or control number of grids/blocks etc. (not that we expect such parameters, just an observation).  Can we assume that the nvBowtie algorithm runs a maximal or optimal number of threads for any given dataset?

thx.

[Jacopo Pantaleoni]

Hi Richard,

unlike on CPUs where it's typical to specify the number of threads for a whole program manually, on GPUs most of the software
is (almost) always trying to automatically maximize occupancy (i.e. hw utilization), which needs careful tuning for each individual
kernel (i.e. the optimal block sizes for different kernels might be different as well, due to differing register or shared memory
utilization, etc).

So yes, nvBowtie tries to select the best grid configuration for each of its many kernels.

(incidentally, on CPUs this is not necessary because their few "fat" cores are oversubscribed with hw resources, but this obviously
comes at a huge cost in energy efficiency)

best,

-jacopo

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