CPU loading issue

[Marc Murphy]

Hello All,
I am using ModemManager to perform GPS logging and it works really well with most modems.

I have a SierraWireless MC7710 and that works beautifully with qmi and logging.
I also have a Huawei MU609 and that works but something slowly causes ModemManager to consume 100% CPU.
We would really like to get the MU609 to work with ModemManager as the price difference is huge and makes the modem viable for low cost.

The MC7710 will sit there all day at about 0.7% CPU which is brilliant
  PID USER      PR  NI    VIRT    RES %CPU %MEM     TIME+ S COMMAND
1015 root      20   0   37.8m   6.1m  0.7   1.2   0:12.85 S  `- ModemManager

The MU609 creeps up 
  PID USER      PR  NI    VIRT    RES %CPU %MEM     TIME+ S COMMAND
1009 root      20   0   37.8m   5.2m  0.0  1.1   0:05.14 S  `- ModemManager
1009 root      20   0   37.8m   5.2m  1.3  1.1   0:05.16 S  `- ModemManager
1009 root      20   0   37.8m   5.2m  4.6  1.1   0:05.23 S  `- ModemManager
1009 root      20   0   37.8m   5.2m  1.3  1.1   0:05.25 S  `- ModemManager
up 9 min
1009 root      20   0   37.8m   5.3m  4.6  1.1   0:15.22 S  `- ModemManager
1009 root      20   0   37.8m   5.3m  9.9  1.1   0:15.37 S  `- ModemManager
1009 root      20   0   37.8m   5.3m  5.3  1.1   0:15.45 S  `- ModemManager
1009 root      20   0   37.8m   5.3m  9.9  1.1   0:15.60 S  `- ModemManager
up 21 min
1009 root      20   0   37.9m   5.4m 20.5  1.1   1:20.14 S  `- ModemManager
1009 root      20   0   37.9m   5.4m 10.5  1.1   1:20.30 S  `- ModemManager
1009 root      20   0   37.9m   5.4m 21.2  1.1   1:20.62 S  `- ModemManager
up 38 min
1009 root      20   0   38.0m   5.4m 47.7  1.1   9:49.07 R  `- ModemManager
1009 root      20   0   38.0m   5.4m 78.9  1.1   9:51.02 R  `- ModemManager
1009 root      20   0   38.0m   5.4m 81.1  1.1   9:52.95 R  `- ModemManager
1009 root      20   0   38.0m   5.4m 79.5  1.1   9:54.85 R  `- ModemManager
1009 root      20   0   38.0m   5.4m 81.1  1.1   9:56.78 R  `- ModemManager

Im wondering where is the best place to look at where the issue could be ?

Is there a processing loop that could be getting stuck ?

Any help appreciated.

Thanks
Marc