Possible contention/blocking in nova-api (100% CPU until untarred) after uploading image

After uploading a 5G image (cloud-publish-image) with kernel and initrd - at the stage it is untarring, euca-describe-images waits until image is not untarring.
I'm aware that this is also dependent on hardware capabilities and may not constitute a bug - but possible uneccessary blocking occuring from one task to the next.

2 x Intel Core Duo E6550 @ 2.33GHz
2Gb RAM
Storage is local disk (SATA)

No swapping occurring.

Commands to reproduce:
$ cloud-publish-image -t image -K CentOS-6.1-i386-vmlinuz-virtual -R CentOS-6.1-i386-loader i386 CentOS-6.1-i386.img images
$ euca-describe-images

Eventually returned this

IMAGE ami-00000011 images/CentOS-6.1-i386.img.manifest.xml untarring private i386 machine aki-0000000f ari-00000010 instance-store
IMAGE ari-00000010 images/CentOS-6.1-i386-loader.manifest.xml available private i386 ramdisk instance-store
IMAGE aki-0000000f images/CentOS-6.1-i386-vmlinuz-virtual.manifest.xml available private i386 kernel

On my host (spec as described), nova-api running 99-100% on a single CPU (untarring image).
Concern is that no other users can use nova-api (and therefore Nova) until task is complete.