Question: bootloader pygrub VS kernel and ramdisk in filesystem of Dom0

[Bobbi Sanchez <bobbisanchez@xxxxxx>]

Hello Xen folks ;-)


while i was reading the Xen Wiki Pages 
https://wiki.xenproject.org/wiki/Tuning_Xen_for_Performance

at the part of:  Tuning your Xen installaton: advenced settings, there are two 
examples in this Manual of howto start a PV Guest. It shows  booting a PV Guest one 
with the bootloader: pygrub

bootloader = "/usr/bin/pygrub"
memory = 1024
name = "linux"
vif = [ "bridge=xenbr0" ]
disk = [ "/root/images/debian_squeeze_amd64_standard.raw,raw,xvda,w" ]
root = "/dev/xvda1"

and the other example from the Xen Wiki shows howto start the PV Guest and boot 
kernel and ramdisk directly from dom0:

kernel = "/boot/vmlinuz"
ramdisk = "/boot/initrd"
memory = 1024
name = "linux"
vif = [ "bridge=xenbr0" ]
disk = [ "/images/debian_squeeze_amd64_standard.raw,raw,xvda,w" ]
root = "/dev/xvda1"

The second example will start the domu without going with the bootloader: 
pygrub and trys otherwise to run kernel and ramdisk directly to load at start 
the PV Guest directly from the dom0.

The first example goes with pygrub and the start of the domu in this case, 
first  loads pygrub, after that pygrub (aka grub) loads the kernel and ramdisk.

So my Question is what makes the differences to start a PV Guest with bootload 
pygrub or load the kernel and ramdisk directly?

What is the difference if I start a PV guest with pygrub or if the kernel and 
ramdisk are loaded directly when starting the PV Guest.

Speed differences, security aspects, more or less flexibility, saving resources?


Thanks a lot.

Best Regards