+==================
Guest halt polling
==================
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/
=============
- 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.