docs: virt: guest-halt-polling.txt convert to ReST

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Guest halt polling

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The cpuidle_haltpoll driver, with the haltpoll governor, allows

the guest vcpus to poll for a specified amount of time before

halting.

This provides the following benefits to host side polling:

	1) The POLL flag is set while polling is performed, which allows

The haltpoll governor has 5 tunable module parameters:

1) guest_halt_poll_ns:

Maximum amount of time, in nanoseconds, that polling is

performed before halting.

Default: 200000

2) guest_halt_poll_shrink:

Division factor used to shrink per-cpu guest_halt_poll_ns when

wakeup event occurs after the global guest_halt_poll_ns.

Default: 2

3) guest_halt_poll_grow:

Multiplication factor used to grow per-cpu guest_halt_poll_ns

when event occurs after per-cpu guest_halt_poll_ns

but before global guest_halt_poll_ns.

Default: 2

4) guest_halt_poll_grow_start:

The per-cpu guest_halt_poll_ns eventually reaches zero

in case of an idle system. This value sets the initial

per-cpu guest_halt_poll_ns when growing. This can

Default: Y

The module parameters can be set from the debugfs files in:

The module parameters can be set from the debugfs files in::

	/sys/module/haltpoll/parameters/

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- Care should be taken when setting the guest_halt_poll_ns parameter as a

large value has the potential to drive the cpu usage to 100% on a machine which

would be almost entirely idle otherwise.

  large value has the potential to drive the cpu usage to 100% on a machine

  which would be almost entirely idle otherwise.

   kvm/index

   uml/user_mode_linux

   paravirt_ops

   guest-halt-polling

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