No, my point was that clone and fork are very similar, and if you ACTUALLY do something in the forked/cloned process, the difference betweent the two process creating mechanisms would be very similar - however, if you don't do anything inside the popen, you get to see the difference. The thing is that popen is meant to spawn a process that actually does something - at least that's the general idea. That is why this sort of microbenchmark that tests a paricular system call is often quite useless - if you where to spawn of a gcc compile, do you think the time taken to actually perform popen would be noticable, compared to the compiling of some kilobytes of source-code [if you use -pipe on gcc I believe it would use popen to create the next level compile]?

Application benchmarks are much more meaningfull for the end users and with the right tools can be used to direct the kernel developers to look at the right areas of the kernel to increase the performance of the system - which is probably not going to be suboptimisations inside popen.