logging through systemd-journald is bottleneck

Dear all, we're currently testing performance of OpenLDAP on Oracle/RedHat Linux and quite unexpected actually hit systemd-journald to be a bottleneck. While OpenLDAP happily makes use of all available CPUs, that one is single threaded, braking everything. The only way around I have found is to set olcLoglevel to 0, speeding up my test run by a factor of 6(!). That now of course is not an option to use in production. I'd happily directly write to a file as I did in the old days but I cannot get olcLogfile to work. And even if I was able to get there, how do I stop OpenLDAP from logging to syslogd (which is inevitably forwarding everything to system-journald ....) ? Can anyone give advice how to handle this ? Any hint appreciated (short of "get a decent OS" - that is not an option). Thanks, Markus