[syslog-ng]Slow capturing syslog

I tested with kiwi syslog generator and I found either syslog-ng or syslogd is putting the log into file destination very slow at fastest exactly 10sec per log. At the rest of the log is queue in buffer. If syslog-ng were to run in environment that has log input with consistently 1 log per second, this will not work even we set the buffer large. Also not real time. I believe this is something to do with the synchronisation of SOCK_STREAM socket because I am using linux. Do you know how to fine tune this. Regards