[vfio-users] CPU Question

[Bradley Davis]

It appears my last message wasn't delivered by google.

What is the feature called that Xeon E5s have that others do not? I'm not
seeing references to ACS on Intel ARC. I have an Intel Xeon X5660 and i'm
trying to see if my processor has the feature. Maybe I just got lucky with
my motherboard having each PCIe slot in its IOMMU group.

On Thu, Sep 3, 2015 at 2:55 PM, Blank Field <ihatethisfield at gmail.com>
wrote:

> There are two ways of assigning CPU cores to the VM:
> 1. The basic one. Just specifies the number of threads that QEMU creates,
> then the OS handles CPU affinity by itself.
> 2. The CPU pinning. Here you specify that QEMU can use logical cores #1,
> 3, 5 and 7 for example.
> Pinning the sibling cores will give you a small performance boost due to
> caching and common(or not) elements, for example, we've pinned logical core
> 1 and logical core 0, where core #1 is a hyper-threaded core from core
> #0(these are called siblings, afair), and we need to transfer data from L1
> cache of core #0 to L1 cache of core #1. Since that cache is in the same
> place(that's actually a deep question), we do it instantly and gain
> performance.
>
> So, there is a thread on the mailing list where aw submitted his tool for
> measuring CPU to CPU latency using netperf.
> It would be profitable for you to assign cores with minimal latency
> between them.
>
> There's the bright side of this - you can assign every core.
> The guest will do less work than expected when the host is loaded enough,
> but the host will work at almost the same speed as usual when the guest is
> loaded, pushing out the QEMU out of CPU.
> In usual gaming proccess, even on my 4 core CPU that situations happen
> very rarely, and i play some CPU-intensive games.
>
> There's a lot of technical detail that i've missed, correct me or ask
> questions, maybe someone smarter than me will answer them precisely right.
>
> 2015-09-03 22:11 GMT+03:00 Daniel <flac at posteo.de>:
>
>> I'm planning to use a i7 6700k (4x 4 Ghz, supports Vt-d) which has
>> hyperthreading. How many cores and how many threads would you assign to the
>> VM? Is it possible to let the host use 4 threads (each connected to a
>> different physical core) and to let the VM use 4 threads (each connected to
>> a different physical core)? So that the VM has access to all 4 physical
>> cores of the CPU to get highest gaming perfomance. I searched around but I
>> didn't find a clear answer.
>>
>> Regards,
>> Daniel
>>
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>
>
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