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linux/drivers/cpuidle/governors/haltpoll.c
Parshuram Sangle 496d0a6485 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>
2024-02-12 17:02:51 +01:00

158 lines
3.9 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* haltpoll.c - haltpoll idle governor
*
* Copyright 2019 Red Hat, Inc. and/or its affiliates.
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
* Authors: Marcelo Tosatti <mtosatti@redhat.com>
*/
#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/time.h>
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/kvm_para.h>
#include <trace/events/power.h>
static unsigned int guest_halt_poll_ns __read_mostly = 200000;
module_param(guest_halt_poll_ns, uint, 0644);
/* division factor to shrink halt_poll_ns */
static unsigned int guest_halt_poll_shrink __read_mostly = 2;
module_param(guest_halt_poll_shrink, uint, 0644);
/* multiplication factor to grow per-cpu poll_limit_ns */
static unsigned int guest_halt_poll_grow __read_mostly = 2;
module_param(guest_halt_poll_grow, uint, 0644);
/* value in us to start growing per-cpu halt_poll_ns */
static unsigned int guest_halt_poll_grow_start __read_mostly = 50000;
module_param(guest_halt_poll_grow_start, uint, 0644);
/* allow shrinking guest halt poll */
static bool guest_halt_poll_allow_shrink __read_mostly = true;
module_param(guest_halt_poll_allow_shrink, bool, 0644);
/**
* haltpoll_select - selects the next idle state to enter
* @drv: cpuidle driver containing state data
* @dev: the CPU
* @stop_tick: indication on whether or not to stop the tick
*/
static int haltpoll_select(struct cpuidle_driver *drv,
struct cpuidle_device *dev,
bool *stop_tick)
{
s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
if (!drv->state_count || latency_req == 0) {
*stop_tick = false;
return 0;
}
if (dev->poll_limit_ns == 0)
return 1;
/* Last state was poll? */
if (dev->last_state_idx == 0) {
/* Halt if no event occurred on poll window */
if (dev->poll_time_limit == true)
return 1;
*stop_tick = false;
/* Otherwise, poll again */
return 0;
}
*stop_tick = false;
/* Last state was halt: poll */
return 0;
}
static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
{
unsigned int val;
/* Grow cpu_halt_poll_us if
* cpu_halt_poll_us < block_ns < guest_halt_poll_us
*/
if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
val = dev->poll_limit_ns * guest_halt_poll_grow;
if (val < guest_halt_poll_grow_start)
val = guest_halt_poll_grow_start;
if (val > guest_halt_poll_ns)
val = guest_halt_poll_ns;
trace_guest_halt_poll_ns_grow(val, dev->poll_limit_ns);
dev->poll_limit_ns = val;
} else if (block_ns > guest_halt_poll_ns &&
guest_halt_poll_allow_shrink) {
unsigned int shrink = guest_halt_poll_shrink;
val = dev->poll_limit_ns;
if (shrink == 0) {
val = 0;
} else {
val /= shrink;
/* Reset value to 0 if shrunk below grow_start */
if (val < guest_halt_poll_grow_start)
val = 0;
}
trace_guest_halt_poll_ns_shrink(val, dev->poll_limit_ns);
dev->poll_limit_ns = val;
}
}
/**
* haltpoll_reflect - update variables and update poll time
* @dev: the CPU
* @index: the index of actual entered state
*/
static void haltpoll_reflect(struct cpuidle_device *dev, int index)
{
dev->last_state_idx = index;
if (index != 0)
adjust_poll_limit(dev, dev->last_residency_ns);
}
/**
* haltpoll_enable_device - scans a CPU's states and does setup
* @drv: cpuidle driver
* @dev: the CPU
*/
static int haltpoll_enable_device(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{
dev->poll_limit_ns = 0;
return 0;
}
static struct cpuidle_governor haltpoll_governor = {
.name = "haltpoll",
.rating = 9,
.enable = haltpoll_enable_device,
.select = haltpoll_select,
.reflect = haltpoll_reflect,
};
static int __init init_haltpoll(void)
{
if (kvm_para_available())
return cpuidle_register_governor(&haltpoll_governor);
return 0;
}
postcore_initcall(init_haltpoll);