Possible spin-problem in nanosleep()
From: Richard B. Johnson
Date: Thu Jun 23 2005 - 07:22:37 EST
The man pages say usleep() is obsolete and one should
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.
In the following 'daemon' was converted to nanosleep(). It
sleeps for 100 milliseconds. Process 'xray' was not converted
and it sleeps for 100 milliseconds also. They used to both
accumulate roughly the same amount of time. They simply sleep,
wake up to sample some status, then go back to sleep. This
is an embedded system that was running for about 10 hours.
PID NAME STA CPU MEM EXE Command line
1 (init) S 0.00 368 8 /sbin/init auto
2 (keventd) S 0.00 368 8
3 (ksoftirqd_CPU0)S 0.00 368 8
4 (kswapd) S 0.00 368 8
5 (bdflush) S 0.00 368 8
6 (kupdated) S 0.00 368 8
10 (syslog) S 0.00 268 4 /sbin/syslog
12 (daemon) S 5.93 260 4 /sbin/daemon
14 (xray) S 0.71 264 8 /bin/xray control
Is this a known problem? Is it going to be fixed? In a possibly
related note, the following:
.... is shown to be spinning, by 'top' not sleeping. This, even though
it is giving up its quantum continuously.
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
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