cpuidle: haltpoll: do not shrink guest poll_limit_ns below grow_start

While adjusting guest halt poll limit, grow block starts at
guest_halt_poll_grow_start without taking intermediate values.
Similar behavior is expected while shrinking the value. This
avoids short interval values which are really not required.

VCPU1 trace (guest_halt_poll_shrink equals 2):

VCPU1 grow 10000
VCPU1 shrink 5000
VCPU1 shrink 2500
VCPU1 shrink 1250
VCPU1 shrink 625
VCPU1 shrink 312
VCPU1 shrink 156
VCPU1 shrink 78
VCPU1 shrink 39
VCPU1 shrink 19
VCPU1 shrink 9
VCPU1 shrink 4

Similar change is done in KVM halt poll flow with below patch:
Link: https://lore.kernel.org/kvm/20211006133021.271905-3-sashal@kernel.org/

Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
[ rjw: Subject edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

cpuidle: haltpoll: Add trace points for guest_halt_poll_ns grow/shrink

Add trace points as are implemented in KVM host halt polling.
This helps tune guest halt polling params.

Signed-off-by: Eiichi Tsukata <eiichi.tsukata@nutanix.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

cpuidle: Use nanoseconds as the unit of time

Currently, the cpuidle subsystem uses microseconds as the unit of
time which (among other things) causes the idle loop to incur some
integer division overhead for no clear benefit.

In order to allow cpuidle to measure time in nanoseconds, add two
new fields, exit_latency_ns and target_residency_ns, to represent the
exit latency and target residency of an idle state in nanoseconds,
respectively, to struct cpuidle_state and initialize them with the
help of the corresponding values in microseconds provided by drivers.
Additionally, change cpuidle_governor_latency_req() to return the
idle state exit latency constraint in nanoseconds.

Also meeasure idle state residency (last_residency_ns in struct
cpuidle_device and time_ns in struct cpuidle_driver) in nanoseconds
and update the cpuidle core and governors accordingly.

However, the menu governor still computes typical intervals in
microseconds to avoid integer overflows.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>

cpuidle-haltpoll: set haltpoll as preferred governor

Right now, guest current governors have the following ratings:

* ladder -> 10
* teo -> 19
* menu -> 20
* haltpoll -> 21
* ladder + nohz=off -> 25

haltpoll governor got introduced and it is now the default governor given
its highest rating -- with ladder+nohz being the exception -- regardless of
idle driver in the guest. An example of an undesirable case is x86 KVM
guests with MWAIT which have intel_idle registered first, and consequently
will have haltpoll be used as governor which would get limited to a poll
state and state 1 and the other states wouldn't get used.

To keep the previous defaults we decrease rating of governor to 9 (below
current lowest rating) and thus rely on @governor switch on
cpuidle_register_driver() to tie in haltpoll idle driver and governor
together.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

cpuidle: add haltpoll governor

The cpuidle_haltpoll governor, in conjunction with the haltpoll cpuidle
driver, allows 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.

Results comparing halt_poll_ns and server/client application
where a small packet is ping-ponged:

host --> 31.33
halt_poll_ns=300000 / no guest busy spin --> 33.40 (93.8%)
halt_poll_ns=0 / guest_halt_poll_ns=300000 --> 32.73 (95.7%)

For the SAP HANA benchmarks (where idle_spin is a parameter
of the previous version of the patch, results should be the
same):

hpns == halt_poll_ns

idle_spin=0/ idle_spin=800/ idle_spin=0/
hpns=200000 hpns=0 hpns=800000
DeleteC06T03 (100 thread) 1.76 1.71 (-3%) 1.78 (+1%)
InsertC16T02 (100 thread) 2.14 2.07 (-3%) 2.18 (+1.8%)
DeleteC00T01 (1 thread) 1.34 1.28 (-4.5%) 1.29 (-3.7%)
UpdateC00T03 (1 thread) 4.72 4.18 (-12%) 4.53 (-5%)

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>