update:
1_ tried to install 3.10-2-rt-686-pae_3.10.7-1_i386.deb from
http://packages.debian.org/jessie/linux-image-3.10-2-rt-686-pae, but it didn't like my initramfs-tools version (apparently too old for the new kernel) and installed without configuration so had to remove. See log:
dpkg: dependency problems prevent configuration of initramfs-tools:
linux-image-3.10-2-rt-686-pae (3.10.7-1) breaks initramfs-tools (<< 0.110~) and is unpacked but not configured.
Version of initramfs-tools to be configured is 0.103ubuntu0.7.
2_ my low-latency kernel is 3.8.0*. I compiled my own rt-kernel, using
http://www.kernel.org/pub/linux/kernel/v3.x/linux-3.2.48.tar.bz2 and its related rt patch, as in the tutorial that Jeremy posted. The kernel compiles and installs fine, but when I load it from grub, Mint load correctly, and then (before seeing anything on screen) my screen goes black. Nothing to do there, tried to use hotkeys to get a tty, restart, or shutdown, but had only to push the power button.