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| author | David Matlack <dmatlack@google.com> | 2022-12-01 11:52:49 -0800 |
|---|---|---|
| committer | Gerd Hoffmann <kraxel@redhat.com> | 2023-01-06 06:27:24 +0100 |
| commit | 545a60f441dea493493ea98213bcd5a667b5e153 (patch) | |
| tree | bfc66f651d3e2902c4fbdb98b85897f046587333 | |
| parent | 5bb52b731c6d529247839eed3ff17b1e743296ee (diff) | |
| download | linux-545a60f441dea493493ea98213bcd5a667b5e153.tar.gz | |
KVM: Document the interaction between KVM_CAP_HALT_POLL and halt_poll_ns
Clarify the existing documentation about how KVM_CAP_HALT_POLL and
halt_poll_ns interact to make it clear that VMs using KVM_CAP_HALT_POLL
ignore halt_poll_ns.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20221201195249.3369720-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 15 | ||||
| -rw-r--r-- | Documentation/virt/kvm/halt-polling.rst | 13 |
2 files changed, 20 insertions, 8 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index eee9f857a986..896914e3a847 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7213,14 +7213,13 @@ veto the transition. :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. +KVM_CAP_HALT_POLL overrides the kvm.halt_poll_ns module parameter to set the +maximum halt-polling time for all vCPUs in the target VM. This capability can +be invoked at any time and any number of times to dynamically change the +maximum halt-polling time. + +See Documentation/virt/kvm/halt-polling.rst for more information on halt +polling. 7.21 KVM_CAP_X86_USER_SPACE_MSR ------------------------------- diff --git a/Documentation/virt/kvm/halt-polling.rst b/Documentation/virt/kvm/halt-polling.rst index 4922e4a15f18..3fae39b1a5ba 100644 --- a/Documentation/virt/kvm/halt-polling.rst +++ b/Documentation/virt/kvm/halt-polling.rst @@ -119,6 +119,19 @@ These module parameters can be set from the debugfs files in: Note: that these module parameters are system wide values and are not able to be tuned on a per vm basis. +Any changes to these parameters will be picked up by new and existing vCPUs the +next time they halt, with the notable exception of VMs using KVM_CAP_HALT_POLL +(see next section). + +KVM_CAP_HALT_POLL +================= + +KVM_CAP_HALT_POLL is a VM capability that allows userspace to override halt_poll_ns +on a per-VM basis. VMs using KVM_CAP_HALT_POLL ignore halt_poll_ns completely (but +still obey halt_poll_ns_grow, halt_poll_ns_grow_start, and halt_poll_ns_shrink). + +See Documentation/virt/kvm/api.rst for more information on this capability. + Further Notes ============= |