It's been a few releases since we introduced the new key: value syntax in benchmark output. When we first introduced it, we left the -P suffix to signal the GOMAXPROCS setting, to avoid disruption for tools that didn't know about the new syntax. At this point I think we can safely move that into the key-value sections, cleaning up the main output lines.
That is, this output from go test -bench=Parallel64 -benchtime=0.1s -count=5 -cpu=1,2,4 -run=XXX net/http:
It's not clear to me that there will be any less tool breakage at this point than there would have been in the past, though I also suspect there aren't many tools outside of the ones we write that particularly care. Do benchstat and benchsave handle this smoothly today? (Do we have any other tools that would care?)