Below are the steps I used to install GNU Radio on the Parallella from the github source. This install includes the Gnuradio-companion, which is a graphical editor for GNU Radio programs. It is a bit heavy, and may feel slow on the board. It is completely optional, and I recommend running/writing GNU Radio programs from the Terminal instead.
One part of the build process involves wrapping c++ code in Python (SWIG), which is very memory intensive; in fact it requires more memory than the board can sustain. To get around the memory shortage, you can choose to remove Python support, and only support c++ GNU Radio programs, but this is not ideal. In order to get everything running with python support, you need to add additional swap space. What I did was use a USB hub to add swap space in the form of a USB memory stick. I also did the build on an external HDD which was also connected via the hub to reduce the wear on the SD card, increase storage space, and to allow for future image updates without losing my source / built files.
Below are the steps:
Install Dependencies
sudo apt-get install libusb-dev python-qt4 python-numpy libtool g++ python-dev swig libboost-all-dev autoconf libcppunit-dev python-lxml python-qwt5-qt4 libqt4-opengl-dev python-cheetah cmake python-wxgtk2.8 libqwt5-qt4-dev fftw3-dev fftw3 libfftw3-dev libqwt5-qt4-dev python-gtk2 libasound2-dev gcc-multilib
Grab Source, Build, and Install
>cd to src directory>
git clone https://github.com/gnuradio/gnuradio.git
cd gnuradio
mkdir build
cmake -Dhave_mfpu_neon=1 -DCMAKE_CXX_FLAGS:STRING="-march=armv7 -mfpu=vfp -mfloat-abi=soft" -DCMAKE_C_FLAGS:STRING="-march=armv7 -mfpu=vfp -mfloat-abi=soft" ../
WARNING: This will take more than 24 hrs, and will slow down your board to an otherwise-unusable state. Both cores are being utilized at near 100% for the build
make -j 2
sudo make install