Analysis of PV(H) build times

["Roger Pau Monné" <roger.pau@citrix.com>]

Hello,

I've done a small analysis of PV and PVH build and launch times using
both xl and a custom builder [1] based on init-xenstore-domain.

The purpose of this analysis is to measure the build time of PV(H)
guests. In order to do this rdtsc calls have been added to the start of
the main xl function and the xen_start_kernel function in Linux (first C
function called by the kernel). The time measured is not only xl build
time, but the time since the xl create call until the guest starts
executing.

The results can be found at:

https://docs.google.com/spreadsheets/d/1xePTI6r1INAIQR901P_lFHFT9ZpduSLpRnKFDl_iB-Q/edit?usp=sharing

A couple of conclusions can be obtained from the results:

 - xl/libxl overhead is very minimal compared to the simple loader
   (~10%). This is probably due to the extra computing done in libxl
   and the fact that the simple loader doesn't populate xenstore paths.

 - Most of time is spent in xc_dom_parse_image (~70%) for both PV and
   PVH domain build.

 - PVH build time is greater than PV by ~10%, due to
   xc_dom_boot_mem_init being more expensive for PVH domains.

Roger.

[1] http://xenbits.xen.org/people/royger/sbuilder.c