Intermittent system hangs on 7.2-RELEASE-p1

[Julian Elischer]

Linda Messerschmidt wrote:
> On Thu, Sep 10, 2009 at 12:57 PM, Ryan Stone<rysto32 at gmail.com> wrote:
>> You should be able to run schedgraph.py on a windows machine with python
>> installed.  It works just fine for me on XP.
> 
> Don't have any of those either, but I *did* get it working on a Mac
> right out of the box.  Should have thought of that sooner. :)
> 
> The output looks pretty straightforward, but there are a couple of
> things I find odd.
> 
> First, there's a point right around what I estimate to be the problem
> time where schedgraph.py indicates gmond (the Ganglia monitor) was
> running uninterrupted for a period of exactly 1 second.  However, it
> also indicates that both CPU's idle tasks were *also* running almost
> continuously during that time (subject to clock/net interrupts), and
> that the run queue on both CPU's was zero for most of that second
> while gmond was allegedly running.

I've noticed that schedgraph tends to show the idle threads slightly
skewed one way or the other.  I think there is a cumulative rounding
error in the way they are drawn due to the fact that they are run so
often.  Check the raw data and I think you will find that you just
need to imagine the idle threads slightly to the left or right a bit.
The longer the trace and the further to he right you are looking
the more "out" the idle threads appear to be.

I saw this on both Linux and Mac python implementations.

> 
> Second, the interval I graphed was about nine seconds.  During that
> time, the PHP command line script made a whole lot of requests: it
> usleeps 50ms between requests, and non-broken requests average about
> 1.4ms.  So even with the stalled request chopping 2 seconds off the
> end, there should be somewhere in the neighborhood of 130 requests
> during the graphed period.  But that php process doesn't appear in the
> schedgraph output at all.
> 
> So that doesn't make a whole lot of sense to me.
> 
> I'll try to get another trace and see if that happens the same way again.
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