And I should have mentioned that you can set the number of cores for actual mining in the ~/.zcash/zcash.conf with the genproclimit parameter. I'm not certain how that plays with the second numeric argument for solveequihash....
While mining with genproclimit=4 in my config, all four CPUs on my machine are maxed out. Then, I stopped mining with the command
~/zcash/src/zcash-cli setgenerate false and performed the following two tests:
With genproclimit=4 in my config and a command with 'solveequihash 2' -- only one CPU is at 100%.
With genproclimit=4 in my config and a command with 'solveequihash 2 2' -- two CPUs are at 100%.
So, it looks like solveequihash uses 1 CPU/thread unless directed to do otherwise. The genproclimit does not impact solveequihash.