Or, if you have a semi-locked down production box and a process that's already gone unusably slow, a quick shell loop that calls pstack on the slow process 10 times will get you a good idea where the process is spending its wall clock time. (I've seen locked-down environments where pstack can be run, but gdb can't.)
Note that pstack will probably take a bit for each stack snapshot it prints. It has to attach as a debugger, walk the stacks, and read the symbol tables each time. It's easy for the whole process to freeze for a second or two, so you probably don't want to do this on a production process that is limping along okay-ish.
