virtualbox lies about available processors on non-hyperthreaded processors

[Jack Howarth]

I consider this bug extremely insidious as it can ruin the performance of linux while virtualbox is running. While setting up Oracle's virtualbox-5.1 on my MacPro 3,1 under Ubuntu 16.10, I was puzzled by the extremely bad system performance that I was seeing. Finally I realized that the Processor tab in virtualbox was showing the total available cores on my machine as 16 and the green bar showing the safe zone was extended to 8 cores. Thus any user on an older machine like mine (which has dual quad-core Harpertown processors) will be told to use twice the recommended number of cores. Once I reduced the cores used from 8 to 4, the system performance dramatically improved. This should be trivial to fix as virtualbox should just check /proc/cpuinfo for the correct values and stop assuming hyperthreading is universally available. I have filed this upstream with Oracle as https://www.virtualbox.org/ticket/16265.

[Jack Howarth (jwhowarth)]

Screen shot of Processor panel in virtualbox 5.1.10 under Ubuntu 16.10 on MacPro 3,1 with dual quad-core Harpertown processors that lack hyperthreading support.

[Jack Howarth (jwhowarth)]

The output of 'cat /proc/cpuinfo' on a MacPro 3,1 with dual quad-core Harpertown processors.

[Jack Howarth (jwhowarth)]

I can also confirm that the Virtualbox 5.1.10 run on a Harpertown machine which reports the following in SystemProfiler

Hardware Overview:

  Model Name: Mac Pro
  Model Identifier: MacPro3,1
  Processor Name: Quad-Core Intel Xeon
  Processor Speed: 2.8 GHz
  Number of Processors: 2
  Total Number of Cores: 8
  L2 Cache (per Processor): 12 MB
  Memory: 10 GB
  Bus Speed: 1.6 GHz
  Boot ROM Version: MP31.006C.B05
  SMC Version (system): 1.25f4
  Serial Number (system): G884810ZXYL
  Hardware UUID: 07931828-CA7B-5776-9F2B-8685D5270A85

So you can see that Virtualbox is currently misrepresenting the available hardware as having 16 cores by blindly assuming that every cpu has hyper threading available in it.

[Jack Howarth (jwhowarth)]

Virtualbox processor panel on OS X with dual quad-core Harpertown processors