From 2cffe9f6b96fece065ee8522673c90e92ef2085d Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Wed, 3 Jul 2019 20:51:28 -0300 Subject: 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 Signed-off-by: Rafael J. Wysocki --- drivers/cpuidle/Kconfig | 11 +++ drivers/cpuidle/governors/Makefile | 1 + drivers/cpuidle/governors/haltpoll.c | 150 +++++++++++++++++++++++++++++++++++ 3 files changed, 162 insertions(+) create mode 100644 drivers/cpuidle/governors/haltpoll.c (limited to 'drivers/cpuidle') diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig index cc8efc56be7d..88727b7c0d59 100644 --- a/drivers/cpuidle/Kconfig +++ b/drivers/cpuidle/Kconfig @@ -33,6 +33,17 @@ config CPU_IDLE_GOV_TEO Some workloads benefit from using it and it generally should be safe to use. Say Y here if you are not happy with the alternatives. +config CPU_IDLE_GOV_HALTPOLL + bool "Haltpoll governor (for virtualized systems)" + depends on KVM_GUEST + help + This governor implements haltpoll idle state selection, to be + used in conjunction with the haltpoll cpuidle driver, allowing + for polling for a certain amount of time before entering idle + state. + + Some virtualized workloads benefit from using it. + config DT_IDLE_STATES bool diff --git a/drivers/cpuidle/governors/Makefile b/drivers/cpuidle/governors/Makefile index 42f44cc610dd..63abb5393a4d 100644 --- a/drivers/cpuidle/governors/Makefile +++ b/drivers/cpuidle/governors/Makefile @@ -6,3 +6,4 @@ obj-$(CONFIG_CPU_IDLE_GOV_LADDER) += ladder.o obj-$(CONFIG_CPU_IDLE_GOV_MENU) += menu.o obj-$(CONFIG_CPU_IDLE_GOV_TEO) += teo.o +obj-$(CONFIG_CPU_IDLE_GOV_HALTPOLL) += haltpoll.o diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c new file mode 100644 index 000000000000..797477bda486 --- /dev/null +++ b/drivers/cpuidle/governors/haltpoll.c @@ -0,0 +1,150 @@ +// 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 + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +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) +{ + int 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, unsigned int block_us) +{ + unsigned int val; + u64 block_ns = block_us*NSEC_PER_USEC; + + /* 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; + + 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; + 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); +} + +/** + * 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 = 21, + .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); -- cgit v1.2.3