Re: [patch 0/3] KVM CPU frequency change hypercalls

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [patch 0/3] KVM CPU frequency change hypercalls
Date	2017-02-23 18:50 +0100
Message-ID	<te5GF-4ww-13@gated-at.bofh.it> (permalink)
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On 03/02/2017 20:09, Radim Krcmar wrote:
> One reason why we have a kernel/userspace split is to allow sharing of
> CPU time.  Each application then its state that the kernel keeps track
> of and saves/restores while time-multiplexing.
> 
> Our frequency scaling interface goes against the idea -- guest kernel
> cannot schedule multiple userspaces on the same vCPU, because they could
> conflict by overriding frequency.
> 
> i.e. our feature implies userspace tasks pinned to isolated vCPUs.

That's bad.  This feature is broken by design unless it does proper
save/restore across preemption.

You don't need a hypercall.  Add a cpufreq driver in DPDK that doesn't
use sysfs, and connect it to a daemon in the host through virtio-serial
or vsock.

Paolo

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Re: [patch 0/3] KVM CPU frequency change hypercalls Paolo Bonzini <pbonzini@redhat.com> - 2017-02-23 18:50 +0100
  Re: [patch 0/3] KVM CPU frequency change hypercalls Marcelo Tosatti <mtosatti@redhat.com> - 2017-02-24 02:20 +0100
    Re: [patch 0/3] KVM CPU frequency change hypercalls Paolo Bonzini <pbonzini@redhat.com> - 2017-02-24 10:20 +0100
      Re: [patch 0/3] KVM CPU frequency change hypercalls Marcelo Tosatti <mtosatti@redhat.com> - 2017-02-24 13:00 +0100
        Re: [patch 0/3] KVM CPU frequency change hypercalls Paolo Bonzini <pbonzini@redhat.com> - 2017-02-24 13:20 +0100
          Re: [patch 0/3] KVM CPU frequency change hypercalls Marcelo Tosatti <mtosatti@redhat.com> - 2017-02-24 14:10 +0100
            Re: [patch 0/3] KVM CPU frequency change hypercalls Paolo Bonzini <pbonzini@redhat.com> - 2017-02-24 16:40 +0100
              Re: [patch 0/3] KVM CPU frequency change hypercalls "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-02-24 18:10 +0100
              Re: [patch 0/3] KVM CPU frequency change hypercalls Marcelo Tosatti <mtosatti@redhat.com> - 2017-02-28 22:20 +0100

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