[vfio-users] cpu usage in guest != cpu usage in host, even with exclusive pinning
quentindeldycke at gmail.com
Tue Apr 5 11:31:43 UTC 2016
I tried a few with unigine valley and cinebench benchmark.
Totally no difference on scores, no dpc latency difference also.
But it is effective for turbostat when pc is in idle:
at default value turbostat reports ~35w (cores of vm all time around 1.5ghz)
at 0 turbostat report 20w (cores of vm around 300-400 mhz (6% busy)
Did not try "real gaming" for the moment. Did this remotely...
On 5 April 2016 at 10:53, Jonathan Scruggs <j.scruggs at gmail.com> wrote:
> I don't know what halt_poll_ns does, but wouldn't setting it to 0 disable
> it and is disabling it bad?
> So, what does halt_poll_ns do anyways?
> On 4 April 2016 at 19:17, Okky Hendriansyah <okky.htf at gmail.com> wrote:
>> On Mon, Apr 4, 2016 at 8:20 AM, Jayme Howard <g.prime at gmail.com> wrote:
>>> Okay wow, Alex. That made a huge difference immediately. That dropped
>>> me from 90% to 33% on the main thread, and all the children are below 10%.
>>> On Sun, Apr 3, 2016 at 8:07 PM, Alex Williamson <
>>> alex.l.williamson at gmail.com> wrote:
>>>> If this is the issue I think it is, the unraid folks bisected this and
>>>> found the culprit as:
>>>> aca6ff2 KVM: dynamic halt-polling
>>>> It seems to be a poor interaction of the halt polling interval vs the
>>>> timer ticks on win10. You can pick a different polling interval with the
>>>> kvm module option halt_poll_ns. The default is 500000. It seemed that
>>>> setting this to 400000 or lower resolves the issue. You can do this via a
>>>> modprobe entry, 'options kvm halt_poll_ns=400000' or on the kernel command
>>>> line with kvm.halt_poll_ns=400000. You can also change it dynamically via
>>>> 'echo 400000 > /sys/module/kvm/parameters/halt_poll_ns'
>> I can also confirm that tuning the halt_poll_ns kvm module parameter on
>> kernel 4.4.5 drops the host CPU usage! Haven't done any game benchmark but
>> from listening to music the CPU load is as low as it is on 4.1.20. Although
>> reducing the value to what Alex (400000) had suggested is probably
>> sufficient, I'm currently trying out the value of 0 for it just like what
>> Unraid 6.20 beta 20 changelog had it set on default . Thanks for the
>> info, Alex.
>> Best regards,
>> Okky Hendriansyah
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>> vfio-users at redhat.com
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