did a simple test under FreeBSD/amd64 on intel atom 1.8GHz
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
main() {
int a;
for(a=0;a<10000000;a++) read(0,(void*)&a,0);
}
takes over 5 seconds (10^10 cycles) to execute system call doing nothing
10^7 times. it did this in a loop so even no cache refill effect should
make a difference.
so 1000 CPU cycles on 2-way superscalar in-order CPU per system call with
everything in L1 cache. for me it is way too much.
Huge overhead of passing through ancient x86 gate descriptors are not
present - FreeBSD uses syscall instruction.
i found that doing other system calls that too do - in effect - nothing,
doesn't change that figure much.
tried to browse FreeBSD sources and found it quite complex.
As i for now don't have dragonfly installed on real computer at present
(VM is not a place to make good test) so could anyone perform that test on
dragonfly?
