syscalls performance

[Mauro Romano Trajber]

I was doing some performance tests of system calls and I find an interesting
behavior.
Using RDTSC to count the CPU cycles, a single call to the getpid() consumes
about 7k of CPU clock cycles and ten calls consume approximately 9,800
cycles.
The fact is that from the second call, the CPU cycles grows at a rate of
about 350 CPU cycles per call.
Why does this happen? There is some hardware optimization when the syscall
ID is already in EAX register ?

Any ideias ?
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