process wakeups

[Daniel P. Berrange]

On Mon, Jul 14, 2008 at 02:57:56PM -0700, Ulrich Drepper wrote:
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> One of the worst problems wrt energy savings we have today are all the
> wakeups processes request.  This is not just an issue for laptops, it
> relevant everywhere.
> 
> To see the size of the problem run the attached systemtap script.  On my
> laptop I see the following output (47 secs runtime):
> 
>   uid | poll select  epoll itimer  futex nanosle signal| process
>  2397 |   16      0      0      0      0       0      0| libvirtd

This isn't libvirtd's fault - we don't use any timeouts, and only
break out of poll() if there's real work todo. In this case it
appears we're being woken up once every 5 seconds, bt a message
from the DBus system bus saying

  NameOwnerChanged (nil)  1.237

and then almost immediately

  NameOwnerChanged 1.237 (nil)

Which basically means that every 6 seconds some app is connecting to
DBus and then almost immediately disconnecting again. What's most annoying
is that I've not actually requested that DBus send me this signal.

Anyway, a systemtap script probing 'unix_stream_connect' identifies the
cuplrits..

# cat conn.stap

probe kernel.function("unix_stream_connect").return {
      if ($return == 0) {
         p = pid()
         n = execname()
        printf ("%d %d %s\n", gettimeofday_s(), p, n)
      }
}
[root at t60wlan ~]# stap conn.stap
1216136855 8215 hal-is-caller-p
1216136855 8217 hal-ipw-killswi
1216136861 8219 hal-is-caller-p
1216136861 8221 hal-ipw-killswi
1216136867 8223 hal-is-caller-p
1216136867 8225 hal-ipw-killswi

Aka 

  /usr/libexec/hal-ipw-killswitch-linux
  /usr/bin/hal-is-caller-privileged

which both seem to be spawned once every 5-6 seconds :-(


Daniel
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