When it comes to extreme tuning, this is how I got +5% performance in one of my tests on 8-cpu machine (contended at mtr_commit()):
gdb -p $(pidof mysqld) -ex "set srv_spin_wait_delay=50" -batch
P.S. was probably worth posting this just to point out that there’re ways to fill the gap between recompile and my.cnf settings :)
domas mituzas 
Hmm. It’s not a stupid trick, it’s a clever trick. And it occurs to me that there’s a possibility of using this to do things like set long_query_time for all threads when there’s a connection pool and setting the global value is useless. But I’m not a gdb wizard like you, so I’ll need to investigate that :)
god bless gdb.
interesting trick
Thats interesting trick…I tried on Mac, it seems to work…Thanks for sharing..even though not sure one can dare to do it on live prod servers :(
Ranges very high in the “Neat Trick” scale…