Foundation_v8 ssh/scp problem

Hello, I am running Foundation_v8 with images from Linaro as follows:

./Foundation_v8 --image=img-foundation.axf --block-device=vexpress64-openembedded_sdk-armv8_20130127-242.img --network=nat --network-nat-ports=8022=22

I noticed that often when I ssd or scp into the target (ssh -p 8022 root@localhost ), the Foundation_v8 would spike to 100% usage on the host for a few minute before ssh would returns which makes the process very slow. Doing "top" in the target shows that 98% of cpu is being used servicing sirq (soft irq). Has anybody seen this and is there a solution? Thanks.