Re: system call library functions

Thanks, all! (Shantonu, Rob, and Justin)

R,
Dow

On Nov 29, 2004, at 1:17 PM, Justin Walker wrote:

>
> On Nov 29, 2004, at 13:06, Dow Street wrote:
>
>> All,
>>
>> I am writing some benchmarking code for OS X 10.3.5.  When using  
>> getpid() to measure the overhead of a system call, I find the  
>> overhead to be much less than expected (1-3 clicks on the MPC 7447a  
>> TBR).  When making the call using syscall(20), however, the  
>> measurement is as expected (~33 clicks on the TBR).  Is getpid  
>> actually using a library function which retrieves the PID from a user  
>> space data structure (without entry into the kernel?)  Any idea what  
>> / where this function is located and the data structure it's  
>> accessing?
>
> The first call to getpid() goes to the kernel; subsequent calls  
> retrieve the pid cached in user space (since a process's PID doesn't  
> change from moment to moment).  That's a bit of a simplification, but  
> check the source.
>
> Cf the file Libc/ppc/sys/getpid.s
>
> Regards,
>
> Justin
>
> --
> Justin C. Walker, Curmudgeon-At-Large  *
> Institute for General Semantics        |   If you're not confused,
>                                        |   You're not paying attention
> *-------------------------------------- 
> *-------------------------------*
>
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