nanosleep sleep 60 microseconds too long - linux

Question

I have the following test compiled in g++ which nanosleep too long , it takes
60 microseconds to finish , I expected it cost only less than 1 microsecond :
int main()
{
gettimeofday(&startx, NULL);
struct timespec req={0};
req.tv_sec=0;
req.tv_nsec=100 ;
nanosleep(&req,NULL) ;
gettimeofday(&endx, NULL);
printf("(%d)(%d)\n",startx.tv_sec,startx.tv_usec);
printf("(%d)(%d)\n",endx.tv_sec,endx.tv_usec);
return 0 ;
}
My environment : uname -r showes :
3.10.0-123.el7.x86_64
cat /boot/config-uname -r | grep HZ
CONFIG_NO_HZ_COMMON=y
# CONFIG_HZ_PERIODIC is not set
# CONFIG_NO_HZ_IDLE is not set
CONFIG_NO_HZ_FULL=y
# CONFIG_NO_HZ_FULL_ALL is not set
CONFIG_NO_HZ=y
# CONFIG_RCU_FAST_NO_HZ is not set
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
# CONFIG_HZ_300 is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_MACHZ_WDT=m
Should I do something in HZ config so that nanosleep will do exactly I expect?!
my cpu information :
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 24
On-line CPU(s) list: 0-23
Thread(s) per core: 2
Core(s) per socket: 6
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 63
Model name: Intel(R) Xeon(R) CPU E5-2643 v3 # 3.40GHz
Stepping: 2
CPU MHz: 3600.015
BogoMIPS: 6804.22
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 20480K
NUMA node0 CPU(s): 0,2,4,6,8,10,12,14,16,18,20,22
NUMA node1 CPU(s): 1,3,5,7,9,11,13,15,17,19,21,23
Edit :
#ifdef SYS_gettid
pid_t tid = syscall(SYS_gettid);
printf("thread1...tid=(%d)\n",tid);
#else
#error "SYS_gettid unavailable on this system"
#endif
this will get tid of the thread I like to high priority , then do
chrt -v -r -p 99 tid to achieve this goal , thanks for Johan Boule
kind help , great appreciate !!!
Edit2 :
#ifdef SYS_gettid
const char *sched_policy[] = {
"SCHED_OTHER",
"SCHED_FIFO",
"SCHED_RR",
"SCHED_BATCH"
};
struct sched_param sp = {
.sched_priority = 99
};
pid_t tid = syscall(SYS_gettid);
printf("thread1...tid=(%d)\n",tid);
sched_setscheduler(tid, SCHED_RR, &sp);
printf("Scheduler Policy is %s.\n", sched_policy[sched_getscheduler(0)]);
#else
#error "SYS_gettid unavailable on this system"
#endif
this will do exact what I want to do without help of chrt

Answer 1

(This is not an answer)
For what is worth, using the more modern functions leads to the same result:
#include <stddef.h>
#include <time.h>
#include <stdio.h>
int main()
{
struct timespec startx, endx;
clock_gettime(CLOCK_MONOTONIC, &startx);
struct timespec req={0};
req.tv_sec=0;
req.tv_nsec=100 ;
clock_nanosleep(CLOCK_MONOTONIC, 0, &req, NULL);
clock_gettime(CLOCK_MONOTONIC, &endx);
printf("(%d)(%d)\n",startx.tv_sec,startx.tv_nsec);
printf("(%d)(%d)\n",endx.tv_sec,endx.tv_nsec);
return 0 ;
}
Output:
(296441)(153832940)
(296441)(153888488)