Same behavior for a new syscall created from scratch. On Friday, February 25, 2011, Enrico Granata <egranata@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@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@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@gmail.com> wrote:
On Fri, Feb 25, 2011 at 8:22 PM, Mauro Romano Trajber <trajber@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>