Several bhyve quirks

Julian Hsiao madoka at
Wed Mar 25 09:30:16 UTC 2015


I'm running bhyve on 10.1, mostly with OpenBSD (5.7) guests, and I ran 
into a few strange issues:

1. The guest RTC is several hours off every time I start bhyve.  The 
host RTC is set to UTC, and /etc/localtime on both the host and guests 
are set to US/Pacific (currently PDT).  I thought maybe bhyve is 
setting the RTC to the local time, and indeed changing TZ environment 
variable affects the guest's RTC.  However, with TZ=UTC the guest is 
still off by an hour, and to get the correct offset I set TZ='UTC+1'; 
perhaps something's not handling DST correctly?

Also, one time the offset was mysteriously tens of hours off (i.e. the 
guest RTS is a day or two ahead), and the condition persisted across 
multiple host and guest reboots.  Unfortunately, the problem went away 
a few hours later and I was unable to reproduce it since.

suggests that I'm on the right track, but it doesn't explain the 
off-by-one nor the (one time) multi-day offset.

As an aside, the commit message implies that this only affects OpenBSD 
guest, when in fact this probably affects all guests (at least also 
Linux).  Perhaps he meant you cannot configure OpenBSD to assume that 
the RTC is set to local time instead of UTC.

2. What's the preferred solution for minimizing guest clock drift in 
bhyve?  Based on some Google searches, I run ntpd in the guests and set 
kern.timecounter.hardware=acpitimer0 instead of the default acpihpet0.  
acpitimer0 drifts by ~600 ppm while acpihpet0 drifts by ~1500 ppm; why?

3. Even moderate guest disk I/O completely kills guest network 
performance.  For example, whenever security(8) (security(7) in 
FreeBSD) runs, guest network throughput drops from 150+ Mbps to ~20 
Mbps, and jitter from ping jumps from <0.01 ms to 100+ ms.  If I try to 
build something in the guest, then network becomes almost unusable.

The network performance degradation only affects the guest that's 
generating the I/O; high I/O on guest B doesn't affect guest A, nor 
would high I/O on the host.

I'm using both virtio-blk and virio-net drivers, and the guests' disk 
images are backed by zvol+geli.  Removing geli has no effect.

There are some commits in CURRENT that suggests improved virtio 
performance, but I'm not comfortable running CURRENT.  Is there a 
workaround I could use for 10.1?

4. virtio-blk always reports the virtual disk as having 512-byte 
sectors, and so I get I/O errors on OpenBSD guests when the disk image 
is backed by zvol+geli with 4K sector size.  Curiously, this only seems 
to affect zvol+geli; with just zvol it seems to work.  Also, it works 
either way on Linux guests.

ATM I changed the zvol / geli sector size to 512 bytes, which probably 
made #2 worse.  I think this bug / feature is addressed by: 
but again is there a workaround to force a specific sector size for 

5. This may be better directed at OpenBSD but I'll ask here anyway: if 
I enable virtio-rnd then OpenBSD would not boot with "couldn't map 
interrupt" error.  The kernel in bsd.rd will boot, but not the 
installed kernel (or the one built from STABLE; I forgot).  Again, 
Linux seems unaffected, but I couldn't tell if it's actually working.

Julian Hsiao

More information about the freebsd-virtualization mailing list