tcmalloc has a lot of parameters, and the defaults are not suited to any workload I've ever seen, so I'd be interested to know if these knobs were turned for this benchmark. Things like total thread cache size make a huge difference. Also note that the tcmalloc being tested here, from the Debian package, lacks the fast-path improvements released in gperftools 2.6, which represented a roll-up of years of internal Google improvements to tcmalloc.