qubes using cpu with 8 cores

[katmai karbonellenc]

I installed QubesOS on new PC, that his CPU have 8 cores but I only can be see 4 cores available.
How I can solve it?
thanks

[799]

Hello,

katmai karbonellenc <katmai...@gmail.com> schrieb am Fr., 19. Apr. 2019, 01:55:

I installed QubesOS on new PC, that his CPU have 8 cores but I only can be see 4 cores available.
How I can solve it?

To solve it, it would be helpful to get some more information:

- what modell is the CPU?

- which Qubes version are using?

- are you looking into the AppVM or into the Hypervisor

Please post the output of:

cat /proc/cpuinfo

xl vcpu-list

Could it be that you mix up the total cores yout system have, against what you can see in an AppVM?

AFAIK dom0 is also just an AppVM on top of Xen and therefore you might see only the cores which are assigned to dom0?

The xl commands should help you.

- O/799

[unman]

You almost certainly dont have 8 cores - you probably have a 4 core CPU
with hyperthreading.
By default Qubes disables hyperthreading for security reasons.

[katmai karbonellenc]

I was trying monitoring all cores from Dom0 but I only can see this cores.
Attached outputs of this commands.

[katmai karbonellenc]

> You almost certainly dont have 8 cores - you probably have a 4 core CPU
> with hyperthreading.
> By default Qubes disables hyperthreading for security reasons.

I have other HDD with Manjaro distribution and works with 8 cores.

The specifications of this CPU:
https://www.intel.co.uk/content/www/uk/en/products/processors/core/i7-processors/i7-7700k.html

[brenda...@gmail.com]

The document says:
# of Cores = 4
# of Threads = 8

So...four cores. Qubes disables hyperthreading (allows a core to appear as two virtual cores) due to security issues with hyperthreading.

Brendan

[katmai karbonellenc]

> The document says:
> # of Cores = 4
> # of Threads = 8
>
> So...four cores. Qubes disables hyperthreading (allows a core to appear as two virtual cores) due to security issues with hyperthreading.
>

sorry, you're right.
The performance is affected when the 'hyperthreading' is disabled?

[unman]

As ever, it's a trade off. Performance will be affected to some extent -
whether you will actually notice depends on the other hardware.

[799]

Hello,

katmai karbonellenc <katmai...@gmail.com> schrieb am Fr., 19. Apr. 2019, 02:29:

> You almost certainly dont have 8 cores - you probably have a 4 core CPU
> with hyperthreading.
> By default Qubes disables hyperthreading for security reasons.

I have looked at the output of the commands:

model name : Intel(R) Core(TM) i7-7700K CPU 

(...)

cpu cores : 4

and you are referring to the right CPU spec sheet

The specifications of this CPU:
https://www.intel.co.uk/content/www/uk/en/products/processors/core/i7-processors/i7-7700k.html

There you can find the information:

# of Cores = 4

# of Threads = 8

(...)

Intel Hyper-Threading Technology = Yes

As such you only have 4 real cores and Qubes is correct telling you this information.

Why deactivate Hyperthreading?

QSB #43: L1 Terminal Fault speculative side channel (XSA-273)

https://www.qubes-os.org/news/2018/09/02/qsb-43/

(...) Part of the mitigation is to disable hyper-threading. This halves the number of CPU cores that the system sees compared to having

hyper-threading enabled, thus reducing system performance.  Since Qubes OS 4.0 uses both PVH and HVM qubes, it is _not_ safe to re-enable hyper-threading.  If you have previously modified the number of virtual CPUs assigned to any qube (the "vcpus" property), it may be necessary to adjust this value in order to account for reduced system performance. (...)

If you are interested in Hyperthreading performance tests, you might be interesting looking into this article:

Intel Hyper Threading Performance With A Core i7 On Ubuntu 18.04 LTS

https://www.phoronix.com/scan.php?page=article&item=intel-ht-2018&num=1

Regards

- O/799

t.

[jrsm...@gmail.com]

There is a ton of information about Hyperthreading, use cases that benefit from it, use cases that don’t, Security issues, benchmarks, and more just a web search away.