syscalls performance

[Mauro Romano Trajber]

Same behavior for a new syscall created from scratch.

On Friday, February 25, 2011, Enrico Granata <egranata at ucsd.edu> wrote:
> We already ruled that out this morning. The code is now using syscall() directly:inline long mygetpid() {     return syscall(SYS_getpid);}
>
>
> Enrico GranataComputer Science & Engineering Department (EBU3B) - Room 3240office phone 858 534 9914University of California, San Diego
>
>
> On Feb 25, 2011, at 12:59 PM, Jim Kukunas wrote:
> On Fri, Feb 25, 2011 at 12:42 PM, Enrico Granata <egranata at ucsd.edu> wrote:
>
>
> I modified the source code to show exactly how many clock ticks it is taking
> for each call. It seems that the behavior hinted by Mauro Romano Trajber is
> actually there:
> [enrico at espresso ~]$ ./syscallperf 15
> 4925
> 1190
> 942
> 942
> 935
> 942
> 636
> 577
> 627
> 621
> 580
> 591
> 565
> 580
> 565
> I am starting to wonder if this depends on the syscall itself OR on some
> call optimization.. any gcc experts around?
>
> From the getpid(2) manpage:
>
>       "Since glibc version 2.3.4, the  glibc  wrapper  function  for  getpid()
>        caches  PIDs,  so  as  to  avoid additional system calls when a process
>        calls getpid() repeatedly."
>
>
> Enrico Granata
> Computer Science & Engineering Department (EBU3B) - Room 3240
> office phone 858 534 9914
> University of California, San Diego
> On Feb 25, 2011, at 12:30 PM, Mauro Romano Trajber wrote:
>
> Sure, the code is attached.
>
> On Fri, Feb 25, 2011 at 5:15 PM, Daniel Baluta <daniel.baluta at gmail.com>
> wrote:
>
> On Fri, Feb 25, 2011 at 8:22 PM, Mauro Romano Trajber <trajber at gmail.com>
> wrote:
> Thanks Enrico and Daniel, you're right. glibc was caching getpid(); but
> this
> is not the root cause of this behavior.
> Going further, I decide to use call getpid without glibc, using
>  syscall(SYS_getpid) to test this behavior and it happened again.
> Calling it once, the test consumes about 7k CPU cycles and 10 calls
> consumes
> about 10k CPU cycles.
> Any ideas ?
>
> Can you post a pointer to your code and information about how you got
> this numbers?
>
> thanks,
> Daniel.
>
> <syscallperf.c>
>