Why is intr taking up so much cpu?

Doug Barton dougb at FreeBSD.org
Wed Jul 21 06:50:31 UTC 2010

On Tue, 20 Jul 2010, Dan Nelson wrote:

> In the last episode (Jul 19), Doug Barton said:
>> On Sun, 18 Jul 2010, Dan Nelson wrote:
>>> You can also use dtrace to get a count of callouts and their time spent.
>>> Run this for a few seconds then hit ^C:
>> Okey dokey, here you go:
>> http://people.freebsd.org/~dougb/normal-dtrace.txt
>> http://people.freebsd.org/~dougb/bad-dtrace.txt
> I don't see any real difference between those two runs, so maybe it's not a
> callout eating your CPU.  How about running this for a few seconds, which
> will print all the stack traces seen during the sampling period:
> dtrace -n 'profile:::profile-276hz { @pc[stack()]=count(); }'
> On an otherwise idle system, you should see most of the counts in cpu_idle,
> with the remainder clustered in whatever code is eating your CPU.

Ok, here's the output from the above:


FYI, I updated to r210317 because mav's latest commits are clock 
related, and it seemed to help. The first flash video I tried to watch 
went all the way through and afterwards intr was around 2% cpu (normally 
it's in the 0.n% range). However, after killing all the stray 
npviewer.bin processes, and killing firefox, it went back down. It took 
watching several videos in a row to get it to the point where intr 
started running away again.



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