Hi all,
I wrote two program given below just for testing .
I want to measure the time that signal takes to travels between two process.
In these program, Two signals are send,
1) SIGUSR1(from sigTime2.c) to sigTime1 process &
2) SIGUSR2 (from sigTime1.c) to sigTime2 process.

---------------------------- sigTime1.c -----------------------------------------
#include "stdio.h"
#include "unistd.h"
#include "signal.h"
#include "sys/time.h"
#include "string.h"
#include "fcntl.h"

struct timeval tv;

void handler(){

int read_ret1, cont, fd, ret, strret, flag = 1, kill_ret, gotPid;
char name[32], block[32];

read_ret1 = gettimeofday(&tv, NULL);
if(read_ret1)
perror("gettimeofday in handler");
else
printf("T1 usec=%ld \n", (long)tv.tv_usec);

if(flag == 0){
kill_ret = kill(gotPid, SIGUSR2);
if(kill_ret < 0)
perror("kill");

}
else{
for(cont = 0; (cont < 1500) && flag ; cont++){
snprintf(name, sizeof name, "/proc/%d/cmdline", cont);

fd = open(name, O_RDONLY);

ret = read(fd, block, sizeof block);
if(ret > 0){
strret = strcmp("./sigTime2", block);
if(strret == 0){
kill_ret = kill(cont, SIGUSR2);
if(kill_ret < 0)
perror("Kill");

gotPid = cont;
flag = 0;
}
}
close(fd);
}
}
}

int main(void){

signal(SIGUSR1, handler);
while(1);

return 0;
}

------------------ sigTime1.c -END -------------------------------------

---------------------- sigTime2.c --------------------------------------
#include "unistd.h"
#include "sys/wait.h"
#include "signal.h"
#include "fcntl.h"
#include "sys/time.h"
#include "string.h"

int fd;
struct timeval tv;
int gotpid;

void time_chk(void){
int ret;

ret = gettimeofday(&tv, NULL);
if(ret)
perror("gettimeofday");
else
printf("T2 usec=%ld\n", (long)tv.tv_usec);
}

void handler(){
time_chk();

kill(gotpid, SIGUSR1);
}

int main(void){
int ret, cont, strret, flag = 1;
char name[32], block[32];

signal(SIGUSR2, handler);

for(cont = 0; cont < 1500 && flag ; cont++){
snprintf(name, sizeof name, "/proc/%d/cmdline", cont);

fd = open(name, O_RDONLY);
ret = read(fd, block, sizeof block);

if(ret > 0){
strret = strcmp("./sigTime1", block);
if(strret == 0){
ret = gettimeofday(&tv, NULL);
if(ret)
perror("gettimeofday");
else
printf("sec=%ld, usec=%ld \n", (long)tv.tv_sec, (long)tv.tv_usec);

kill(cont, SIGUSR1);
flag = 0;
gotpid = cont;
}
}
close(fd);
}

while(1);

return 0;
}

--------------- sigTime2.c - END -------------------------------------

------------------------------------ OutPut --------------------------
# ./sigTime1 &
# ./sigTime2
sec=2129097828, usec=870277
T1 usec=873027
T2 usec=4990
T1 usec=6010
T2 usec=135988
T1 usec=136982
T2 usec=267988
T1 usec=268982
T2 usec=399987
T1 usec=400982
T2 usec=531084
T1 usec=531987
T2 usec=660997
T1 usec=663958
T2 usec=813001
T1 usec=815001
T2 usec=966988
T1 usec=967981
T2 usec=91992
T1 usec=93009
T2 usec=217012
T1 usec=219040
T2 usec=341988
T1 usec=342982
T2 usec=467986
T1 usec=469977
T2 usec=593988
T1 usec=594982
T2 usec=717988
T1 usec=718983
T2 usec=843971
T1 usec=845972
T2 usec=969990
T1 usec=970982
T2 usec=93989
T1 usec=94981
T2 usec=217988
T1 usec=218982
T2 usec=342989
T1 usec=343981
T2 usec=467986
T1 usec=469012
T2 usec=593013
T1 usec=593983
T2 usec=717988
T1 usec=718983
T2 usec=843982
T1 usec=845081

-------------------------------- OutPut - END ------------------------------------------

So my Question is

The difference between T1 & T2 (845081 - 843982 = 1099 us) is Correct. The value of HZ = 1000
But the difference between T2 & T1 is (843982 - 718983 = 124999 us ).

So the question is, why the time difference between T2 & T1 is so high ?

Thanks in Advance