We already ruled that out this morning. The code is now using syscall() directly: inline long mygetpid() { return syscall(SYS_getpid); }
Computer Science & Engineering Department (EBU3B) - Room 3240 office phone 858 534 9914 University 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@xxxxxxxx> 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@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@xxxxxxxxx>
wrote:
On Fri, Feb 25, 2011 at 8:22 PM, Mauro Romano Trajber <trajber@xxxxxxxxx>
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>
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