Utility of PV on non-obsolete hardware

[tg%gmplib.org@localhost (Torbjörn Granlund)]

I recently realised that GNU/Linux PV guests run poorly compared to PVH
and HVM guests.  I only noticed that since my FreeBSD PVHVM guests
greatly outperformed any other guests.

Now I tested a HVM guest for NetBSD 8.0 (-STABLE) on 3 random machines.
The following table indicates wall clock build times for configure+make
of a package (the GMP bignum library):

                  PV    HVM      HVM speedup
AMD k10           282   207         36%
Intel Goldmont    585   329         78%
Intel Broadwell   225   188         20%

The HVM guests here do not use any PV or Virtio drivers, so any I/O will
pay a toll.  Still, the speedup with HVM is huge.

Perhaps a caution about not using PV should be added to the NetBSD web?
:-)

Seriously, plain PV is perhaps only useful on machines without EPT/NPT.
Our test systems with Intel Conroe (2006), Intel Penryn (2007), and AND
K8 (2003) are the only ones which benefit from PV.

-- 
Torbjörn
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