In a good OS (I believe Linux qualifies), you only need to save the contents of the registers. Each process has its own address space, each thread has its own stack, and so there's no need to much around with memory beyond that. Stacks aren't actually copied around, the processor simply restores %esp and %ebp from the saved process data structure.
IIR my OS design course correctly, the big performance hit is the switch from user mode to kernel mode. I'm not sure *why* that's a big hit, but it seems to be a slow operation on most processors.
You can use user-mode threading libraries in C/C++, but Apache doesn't. Perhaps that's why it's slow. (The main reason it doesn't is probably that user-mode threading blocks the whole process when one thread performs IO, which obviously doesn't work well in an I/O bound application like a webserver.)
There are other C/C++ webservers - like Lighttpd - that use poll/epoll for I/O. These should run even faster than YAWS/Erlang; anyone have any benchmarks to compare them?
IIR my OS design course correctly, the big performance hit is the switch from user mode to kernel mode. I'm not sure *why* that's a big hit, but it seems to be a slow operation on most processors.
You can use user-mode threading libraries in C/C++, but Apache doesn't. Perhaps that's why it's slow. (The main reason it doesn't is probably that user-mode threading blocks the whole process when one thread performs IO, which obviously doesn't work well in an I/O bound application like a webserver.)
There are other C/C++ webservers - like Lighttpd - that use poll/epoll for I/O. These should run even faster than YAWS/Erlang; anyone have any benchmarks to compare them?