[vfio-users] Optimize vm and host performance, is dual xeon the way ?

[Karsten Elfenbein]

It just hands the layout of your CPU to the guest. So apps can decide
on threading.

Pinning the CPU to avoid CPU 0 and 4 will reduce the performance a bit
as a complete physical core is reserved for the host OS.
There are faster Desktop CPUs to compensate if needed but dual Xeon
that can keep up in single thread performance are expensive and you
would need 2 CPU + memory + board.



2015-12-28 10:24 GMT+01:00 Eddie Yen <missile0407 at gmail.com>:
>
> This should provide the guest some details of the provided vCPUs:
>
> <topology sockets='1' cores='3' threads='2'/>
>
>
> I tested this method before, using the 4820K.
> The result I got is the performance not get better that set whole threads as
> cores when tested 3DMark.
> But I didn't pinning 0 and 4 thread to host.
>
> I'll test it again soon.
>
> 2015-12-28 17:13 GMT+08:00 Karsten Elfenbein <karsten.elfenbein at gmail.com>:
>>
>> Hi,
>>
>> that looks good. Processors 0 and 4 are not used in pinning and remain
>> on the host OS. https://en.wikipedia.org/wiki/Hyper-threading
>> Basically as soon as you load one OS CPU on a physical core the other
>> HT core will be able to perform a lot less stuff.
>>
>> This should provide the guest some details of the provided vCPUs:
>> <topology sockets='1' cores='3' threads='2'/>
>>
>>
>> 2015-12-28 6:55 GMT+01:00 thibaut noah <thibaut.noah at gmail.com>:
>> > So is this the right emulation? If i understand correctly what i'm
>> > trying to
>> > get is a 3cores with 2threads per core ? (so 6cores pinned?)
>> > I don't have that much knowledge in cpu so i'm kinda lost here.
>> >
>> > <cputune>
>> >     <vcpupin vcpu='0' cpuset='1'/>
>> >     <vcpupin vcpu='1' cpuset='2'/>
>> >     <vcpupin vcpu='2' cpuset='3'/>
>> >     <vcpupin vcpu='3' cpuset='5'/>
>> >     <vcpupin vcpu='4' cpuset='6'/>
>> >     <vcpupin vcpu='5' cpuset='7'/>
>> >   </cputune>
>> >
>> > 2015-12-26 18:53 GMT+01:00 Karsten Elfenbein
>> > <karsten.elfenbein at gmail.com>:
>> >>
>> >> check that the 2 cores for the host OS are on the same physical core
>> >> and that the VM does not use those 2 processors with the same core id
>> >>
>> >> cat /proc/cpuinfo | grep -e processor -e 'core id'
>> >>
>> >> CPU 0-3 should be the core 0-3
>> >> CPU 4-7 should be the core 0-3 again with HT
>> >>
>> >> so leaving out CPU 0 and 4 should keep core 0 idle and the host OS
>> >> responsive
>> >>
>> >> taskset 1-3,5-7 startVM.sh
>> >>
>> >> Karsten
>> >>
>> >> 2015-12-26 12:56 GMT+01:00 Eddie Yen <missile0407 at gmail.com>:
>> >> > Pining CPU can reduce the happening that host and guest using the
>> >> > same
>> >> > thread at the same time.
>> >> >
>> >> > And I don't know which program you're using on Fedora, so I don't
>> >> > have
>> >> > quite
>> >> > answer that 2 threads is enough for host or not.
>> >> > It's all depends on your usage case.
>> >> >
>> >> > 2015-12-26 19:44 GMT+08:00 thibaut noah <thibaut.noah at gmail.com>:
>> >> >>
>> >> >> My cpu is a i7 4790k, is pinning the cpu usefull ? I'll try to derp
>> >> >> a
>> >> >> bit
>> >> >> with the vcpu thing, just afraid 2 threads aren't enough for fedora
>> >> >> :/
>> >> >>
>> >> >> 2015-12-26 11:59 GMT+01:00 Eddie Yen <missile0407 at gmail.com>:
>> >> >>>
>> >> >>> I forgot your CPU type, so I don't know about your case.
>> >> >>>
>> >> >>> But, as I'm using 4820K, I usually using 4 to 6 threads gave to VM,
>> >> >>> only
>> >> >>> use 2 threads for Fedora host.
>> >> >>> And most important is vCPU tweaks, especially CPU topology and
>> >> >>> Hyper-V.
>> >> >>>
>> >> >>> For me, I usually set topology as "sockets=1 cores=6 threads=1" if
>> >> >>> using
>> >> >>> 6 threads from host.
>> >> >>> Then set cpuset= to let vCPU worked on pointed CPU threads.
>> >> >>>
>> >> >>> IME, set all threads as vCPU cores can got better performance on
>> >> >>> Windows
>> >> >>> 10.
>> >> >>>
>> >> >>> 2015-12-26 18:00 GMT+08:00 thibaut noah <thibaut.noah at gmail.com>:
>> >> >>>>
>> >> >>>> Hello guys merry christmas ! o/
>> >> >>>> My current issue is vm and host optimization, i use my windows 10
>> >> >>>> vm
>> >> >>>> for
>> >> >>>> gaming purposes only (like most of us i think), problem is, to
>> >> >>>> keep
>> >> >>>> my
>> >> >>>> performances on windows high i drain too much ressources on my
>> >> >>>> fedora
>> >> >>>> host
>> >> >>>> thus making it almost useless (also when leaving the vm i most of
>> >> >>>> the
>> >> >>>> time
>> >> >>>> found myself unable to use fedora at all so i have to reboot...).
>> >> >>>> So is it possible to improve performances to the max on the guest
>> >> >>>> without almost killing the host ?
>> >> >>>> Should i consider switching my gear for a bi-xeon? (to assign one
>> >> >>>> fully
>> >> >>>> to the host and one to the guest)
>> >> >>>> I'm actually not sure about what happen here, does anyone ran into
>> >> >>>> the
>> >> >>>> same sort of issue?
>> >> >>>> Have a good day
>> >> >>>>
>> >> >>>> _______________________________________________
>> >> >>>> vfio-users mailing list
>> >> >>>> vfio-users at redhat.com
>> >> >>>> https://www.redhat.com/mailman/listinfo/vfio-users
>> >> >>>>
>> >> >>>
>> >> >>
>> >> >
>> >> >
>> >> > _______________________________________________
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>> >> > https://www.redhat.com/mailman/listinfo/vfio-users
>> >> >
>> >
>> >
>
>