[LUG] Interesting diagnostic problem

[John Daragon <john@xxxxxxxxxx>]

I'm looking at a problem that occurs in the asterisk PABX, and I'm 
running out of inexpensive techniques, so I thought I'd canvas for ideas.

Here's the problem : One of the boards supported by asterisk is the 
Digium TDM4xx 4 port analogue board - 4 ports of PSTN goodness on a 
single PCI card.

This card has a module driver, and when the driver is loaded, even if 
the card is idle and the devices are not open, there's a blip of about 
25% CPU every 5 or 6 seconds.

Top says this CPU is being used by hardware interrupt routines (which 
sounds reasonable as we can stop this by unloading the driver...)

I'm trying to ascertain which routine is using CPU unreasonably.

My first thought was to implement an in-kernel count of entries into 
each function. Alas, this differs little from second to second, so 
whatever is happening is happening within a routine.

What I'd really like to measure is the cumulative time spent in each 
function, but the board raises an interrupt every millisecond, and I 
guess that while the driver is handling this, there just isn't going to 
be a timer interrupt.

Anyone know the real resolution of the hardware RTC ? Any other ideas ?

Anyone know of a cheap(ish) microsecond clock board ?


jd

--

John Daragon                                          john@xxxxxxxxxx
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Lambs Lawn Cottage,  Staple Fitzpaine,  Taunton,  TA3 5SL,  UK
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