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kvm: add capability for halt polling

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KVM_CAP_HALT_POLL is a per-VM capability that lets userspace
control the halt-polling time, allowing halt-polling to be tuned or
disabled on particular VMs.

With dynamic halt-polling, a VM's VCPUs can poll from anywhere from
[0, halt_poll_ns] on each halt. KVM_CAP_HALT_POLL sets the
upper limit on the poll time.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Jon Cargille <jcargill@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200417221446.108733-1-jcargill@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack
2020-04-17 15:14:46 -07:00
committed by Paolo Bonzini
parent 87796555d4
commit acd05785e4
4 changed files with 34 additions and 4 deletions
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17
Documentation/virt/kvm/api.rst
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@@ -5802,6 +5802,23 @@ If present, this capability can be enabled for a VM, meaning that KVM
will allow the transition to secure guest mode. Otherwise KVM will
veto the transition.
7.20 KVM_CAP_HALT_POLL
----------------------
:Architectures: all
:Target: VM
:Parameters: args[0] is the maximum poll time in nanoseconds
:Returns: 0 on success; -1 on error
This capability overrides the kvm module parameter halt_poll_ns for the
target VM.
VCPU polling allows a VCPU to poll for wakeup events instead of immediately
scheduling during guest halts. The maximum time a VCPU can spend polling is
controlled by the kvm module parameter halt_poll_ns. This capability allows
the maximum halt time to specified on a per-VM basis, effectively overriding
the module parameter for the target VM.
8. Other capabilities.
======================