Re: [sup-devel] really high wakeup count in powertop

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Chris Mason's message of 2010-11-09 19:40:58 -0500:
> Hi everyone,
> 
> I'm new to sup and really like the interface and the features.  But, I
> popped up powertop while it was running and sup accounts for a constant 100
> wakeups/second, much more than the one or two wakeups/sec from our old
> friend mutt.
> 
> I haven't done much ruby but can make my way through most things.  If
> someone could point me at the polling function most likely to cause the
> wakeups I can work out a patch.
> 
> I'm running git from this Monday, so pretty recent.  Ruby 1.9.1

(This got dumped into the moderator approval queue, so I'm resending,
this time with more details)

strace showed we were hammering on futexes, and a little digging made it
clear sup isn't to blame.  The ruby timer thread is polling for
signals (or something) every 10ms:

http://redmine.ruby-lang.org/issues/show/3436

I patched up ruby to poll every 500ms and things seem to work.  Not sure
why the ruby developers didn't just change the timeout, but chances are
good they have a real reason.  I'll post to that bug.

-chris
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