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author | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2019-09-17 10:41:26 +0300 |
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committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2019-09-17 10:41:26 +0300 |
commit | 2cdd5cc7032636d5f17822c6ba30ac08bfd2cb6d (patch) | |
tree | 3ace6419f1564ed668781425877a24e9080406f6 /Documentation | |
parent | d2817063697747a8c9dcb971b2eb8f07fc153e5a (diff) | |
parent | 1328edca4a142ee3c7442d1eece2c3ca383eff35 (diff) | |
download | linux-2cdd5cc7032636d5f17822c6ba30ac08bfd2cb6d.tar.xz |
Merge branch 'pm-cpuidle'
* pm-cpuidle:
cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available
cpuidle-haltpoll: do not set an owner to allow modunload
cpuidle-haltpoll: return -ENODEV on modinit failure
cpuidle-haltpoll: set haltpoll as preferred governor
cpuidle: allow governor switch on cpuidle_register_driver()
powercap: idle_inject: Use higher resolution for idle injection
cpuidle: play_idle: Increase the resolution to usec
cpuidle-haltpoll: vcpu hotplug support
cpuidle: teo: Get rid of redundant check in teo_update()
cpuidle: teo: Allow tick to be stopped if PM QoS is used
cpuidle: menu: Allow tick to be stopped if PM QoS is used
cpuidle: header file stubs must be "static inline"
cpuidle-haltpoll: disable host side polling when kvm virtualized
cpuidle: add haltpoll governor
governors: unify last_state_idx
cpuidle: add poll_limit_ns to cpuidle_device structure
add cpuidle-haltpoll driver
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/virtual/guest-halt-polling.txt | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/Documentation/virtual/guest-halt-polling.txt b/Documentation/virtual/guest-halt-polling.txt new file mode 100644 index 000000000000..b3a2a294532d --- /dev/null +++ b/Documentation/virtual/guest-halt-polling.txt @@ -0,0 +1,78 @@ +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 + a remote vCPU to avoid sending an IPI (and the associated + cost of handling the IPI) when performing a wakeup. + + 2) The VM-exit cost can be avoided. + +The downside of guest side polling is that polling is performed +even with other runnable tasks in the host. + +The basic logic as follows: A global value, guest_halt_poll_ns, +is configured by the user, indicating the maximum amount of +time polling is allowed. This value is fixed. + +Each vcpu has an adjustable guest_halt_poll_ns +("per-cpu guest_halt_poll_ns"), which is adjusted by the algorithm +in response to events (explained below). + +Module Parameters +================= + +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 +be increased from 10000, to avoid misses during the initial +growth stage: + +10k, 20k, 40k, ... (example assumes guest_halt_poll_grow=2). + +Default: 50000 + +5) guest_halt_poll_allow_shrink: + +Bool parameter which allows shrinking. Set to N +to avoid it (per-cpu guest_halt_poll_ns will remain +high once achieves global guest_halt_poll_ns value). + +Default: Y + +The module parameters can be set from the debugfs files in: + + /sys/module/haltpoll/parameters/ + +Further Notes +============= + +- 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. |