Doing a getitimer() immediately after a setitimer() on ITIMER_PROF returns the value incremented by 4ms. I can reproduce the issue with itimer values less than 1s.
I verified that this issue does not occur on CentOS (kernel 2.6 from Dec 2009). I checked the source code for kernel/itimer.c, and the following commit in 2011 seems relevant: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/kernel/itimer.c?id=648616343cdbe904c585a6c12e323d3b3c72e46f I do not understand the source fully to confirm that the issue is due to the above commit. Test program: #include <sys/time.h> #include <sys/syscall.h> #include <unistd.h> #include <iostream> int main(int argc, char** argv) { struct itimerval ts; ts.it_value.tv_sec = 0; ts.it_value.tv_usec = 8000; ts.it_interval.tv_sec = 0; ts.it_interval.tv_usec = 8000; for (int i = 0; i < 10; ++i) { syscall(SYS_setitimer, ITIMER_PROF, &ts, NULL); syscall(SYS_getitimer, ITIMER_PROF, &ts); std::cout << "Got back itimer value of " << ts.it_interval.tv_sec << ", " << ts.it_interval.tv_usec << "\n"; } } My current setup: /proc/version: Linux version 3.8.0-19-generic (buildd@allspice) (gcc version 4.7.3 (Ubuntu/Linaro 4.7.3-1ubuntu1) ) #29-Ubuntu SMP Wed Apr 17 18:16:28 UTC 2013 /proc/cpuinfo: processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 58 model name : Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz stepping : 9 cpu MHz : 2379.182 cache size : 6144 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx rdtscp lm constant_tsc rep_good nopl pni ssse3 lahf_lm bogomips : 4758.36 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: Sashi. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
