Andreas,
Additional input: It seems that it's not the usleep(), but
some kind of scheduling phenomena makes the difference.
The following code will show different amounts of CPU time
after a few hours of running on an otherwise unused
system (not even a network card), a real "quiet" system.
The first task forked() seems to get about 5 times the CPU
time of the second. Since the first task used nanosecond()
it was blamed on nanosecond(), but instead it seems to have
something to do with the order in which children are created.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
int main(int argx, char *argv[])
{
volatile int i;
struct timespec ts;
switch(fork())
{
case 0: // Child
strcpy(argv[0], "Using nanosleep()");
for(;;)
{
ts.tv_sec = 0;
ts.tv_nsec = 1000000; // 1 milisecond
(void)nanosleep(&ts, NULL);
for(i=0; i< 0x00010000; i++) // Do work
;
}
break;
case -1: // Failure
abort();
break;
default:
break;
}
switch(fork())
{
case 0: // Child
strcpy(argv[0], "Using usleep()");
for(;;)
{
(void)usleep(1000); // 1 millisecond
for(i=0; i< 0x00010000; i++) // Do work
;
}
break;
case -1: // Failure
abort();
break;
default:
break;
}
pause();
return 0;
}
On Thu, 23 Jun 2005, Richard B. Johnson wrote:
On Thu, 23 Jun 2005, Andreas Schwab wrote:
"Richard B. Johnson" <[email protected]> writes:
nanosleep() appears to have a problem. It may be just an
'accounting' problem, but it isn't pretty. Code that used
to use usleep() to spend most of it's time sleeping, used
little or no CPU time as shown by `top`. The same code,
converted to nanosleep() appears to spend a lot of CPU
cycles spinning. The result is that `top` or similar
programs show lots of wasted CPU time.
usleep() is just a wrapper around nanosleep(). Are you sure you got the
units right?
Andreas.
Yeah nano is -9 micro is -6, three more zeros when using nano.
I note that the actual syscall is __NR_nanosleep = 162. I don't
understand the discrepancy either.
--
Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux Products GmbH, Maxfeldstra�e 5, 90409 N�rnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
Notice : All mail here is now cached for review by Dictator Bush.
98.36% of all statistics are fiction.
Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
Notice : All mail here is now cached for review by Dictator Bush.
98.36% of all statistics are fiction.
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