Lines Matching +full:global +full:- +full:halt

1 .. SPDX-License-Identifier: GPL-2.0
4 The KVM halt polling system
7 The KVM halt polling system provides a feature within KVM whereby the latency
16 the order of a few micro-seconds, although performance benefits are workload
19 invoked. Thus halt polling is especially useful on workloads with very short
20 wakeup periods where the time spent halt polling is minimised and the time
23 The generic halt polling code is implemented in:
27 The powerpc kvm-hv specific case is implemented in:
31 Halt Polling Interval
35 as the halt polling interval, is increased and decreased based on the perceived
39 	kvm_vcpu->halt_poll_ns
41 or in the case of powerpc kvm-hv, in the vcore struct:
43 	kvmppc_vcore->halt_poll_ns
47 During polling if a wakeup source is received within the halt polling interval,
51 the global max polling interval (see module params below), or the total block
52 time was greater than the global max polling interval.
55 the global max polling interval then the polling interval can be increased in
62 In the event that the total block time was greater than the global max polling
63 interval then the host will never poll for long enough (limited by the global
75 		      the time between when the halt polling function is
82 The kvm module has 4 tunable module parameters to adjust the global max polling
86 arch/powerpc/kvm/book3s_hv.c in the powerpc kvm-hv case.
88 +-----------------------+---------------------------+-------------------------+
90 +-----------------------+---------------------------+-------------------------+
91 |halt_poll_ns		| The global max polling    | KVM_HALT_POLL_NS_DEFAULT|
96 +-----------------------+---------------------------+-------------------------+
98 |			| halt polling interval is  |			      |
102 +-----------------------+---------------------------+-------------------------+
107 +-----------------------+---------------------------+-------------------------+
109 |			| halt polling interval is  |			      |
113 +-----------------------+---------------------------+-------------------------+
119 Note: these module parameters are system-wide values and are not able to
123 next time they halt, with the notable exception of VMs using KVM_CAP_HALT_POLL
130 on a per-VM basis. VMs using KVM_CAP_HALT_POLL ignore halt_poll_ns completely (but
138 - Care should be taken when setting the halt_poll_ns module parameter as a large value
142   global max polling interval (halt_poll_ns) then the host will always poll for the
145 - Halt polling essentially presents a trade-off between power usage and latency and
150 - Halt polling will only be conducted by the host when no other tasks are runnable on