[Asterisk-Users] Interrupt latency problems

[Steven Critchfield]

On Wed, 2004-12-01 at 13:12 -0500, Steve Clark wrote:
> Michael Welter wrote:
> > I'm debugging a TxFax problem whereby the fax transmission fails.  I 
> > suspect interrupt latency--some interrupt routine is holding its 
> > interrupt too long.  I have all unnecessary services switched off and X 
> > is not running when I perform these tests.  Some transmission are 
> > successful while others fail at random points.
> > 
> > I've noticed that after I boot Linux, load zaptel, wcfxo, and wcfxs, and 
> > then run System Monitor, the CPU utilization spikes to 60% every 10 
> > seconds.  After I remove wcfxs the spikes stop, and system utilization 
> > stays at 0%.
> > 
> > I have two TDM22B cards and get these spikes with either card in the system.
> > 
> > This is an Athlon-64 3000+ CPU and Fedora Core 2.  zaptel-1.0.2.
> > 
> > Is there anyone who has a TDM card on a "quiet" system who can run 
> > System Monitor and observe CPU utilization?
> > 
> > Thanks for your help.
> > 
> > P.S.  I do 'hdparm -u1 /dev/hdx' on the disks.
> > 
> > 
> 
> I have a athlon xp 1600 with a gig of memory a tdm40 with 2 fxs ports and a 
> t100p t1 hooked to a audiocoded tp260 and see minimal cpu utilization when idle.
> 
> run top and see what is using the cpu.

top will only report userspace problems, and to top it off, top only
reports on snapshots of the system on as low as 1 second. With Zap
hardware hitting the system 1000 times a second for service, you might
happen to get an occasional hit time here top and the hardware hit
pretty close to show extra load. top also has the problem of effecting
the system it is watching. It is a lot like those pesky physics problems
where what you use to measure changes the object your measuring.

Basically all that is to say that top probably won't tell you what you
want to know.About the only thing that would be of interest is if the
percentage is viewed in the system or userspace portions. If in system,
you will have to go debugging the kernel. 

Of course, it seems this is mostly being reported against RH and FC.
I'll take a quick guess that it isn't bad users so it would leave you
with bad kernels. My personal opinion is to not trust what the distros
do to the kernels. Even in my beloved Debian I don't trust the default
kernel. I suggest you download a stock vanila kernel from kernel.org and
config it as minimally as possible for your hardware and try and see if
it reproduces the problems you are seeing currently. 

-- 
Steven Critchfield <critch at basesys.com>