# parallel_on_X has less synchronization overhead than

# parallel_on_Y and should therefore be used whenever

# n_samples_X is large enough to not starve any of the

# available hardware threads.

if self.n_samples_Y < self.n_samples_X:

# No point to even consider parallelizing on Y in this case. This

# is in particular important to do this on machines with a large

# number of hardware threads.

strategy = 'parallel_on_X'

elif 4 * self.chunk_size * self.effective_n_threads < self.n_samples_X:

# If Y is larger than X, but X is still large enough to allow for

# parallelism, we might still want to favor parallelizing on X.