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![Nicholas Piggin](/assets/img/avatar_default.png)
For shared processor guests (e.g., KVM), add an idle polling mode rather than immediately returning to the hypervisor when the guest CPU goes idle. Test setup is a 2 socket POWER9 with 4 guests running, each with vCPUs equal to 1/2 of real of CPUs. Saturated each guest with tbench. Using polling idle gives about 1.4x throughput. Kernel compile speed was not changed significantly. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
295 lines
6.4 KiB
C
295 lines
6.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* cpuidle-pseries - idle state cpuidle driver.
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* Adapted from drivers/idle/intel_idle.c and
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* drivers/acpi/processor_idle.c
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*
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/moduleparam.h>
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#include <linux/cpuidle.h>
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#include <linux/cpu.h>
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#include <linux/notifier.h>
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#include <asm/paca.h>
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#include <asm/reg.h>
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#include <asm/machdep.h>
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#include <asm/firmware.h>
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#include <asm/runlatch.h>
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#include <asm/plpar_wrappers.h>
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struct cpuidle_driver pseries_idle_driver = {
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.name = "pseries_idle",
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.owner = THIS_MODULE,
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};
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static int max_idle_state __read_mostly;
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static struct cpuidle_state *cpuidle_state_table __read_mostly;
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static u64 snooze_timeout __read_mostly;
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static bool snooze_timeout_en __read_mostly;
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static inline void idle_loop_prolog(unsigned long *in_purr)
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{
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ppc64_runlatch_off();
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*in_purr = mfspr(SPRN_PURR);
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/*
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* Indicate to the HV that we are idle. Now would be
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* a good time to find other work to dispatch.
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*/
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get_lppaca()->idle = 1;
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}
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static inline void idle_loop_epilog(unsigned long in_purr)
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{
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u64 wait_cycles;
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wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles);
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wait_cycles += mfspr(SPRN_PURR) - in_purr;
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get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles);
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get_lppaca()->idle = 0;
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ppc64_runlatch_on();
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}
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static int snooze_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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u64 snooze_exit_time;
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set_thread_flag(TIF_POLLING_NRFLAG);
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idle_loop_prolog(&in_purr);
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local_irq_enable();
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snooze_exit_time = get_tb() + snooze_timeout;
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while (!need_resched()) {
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HMT_low();
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HMT_very_low();
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if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
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/*
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* Task has not woken up but we are exiting the polling
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* loop anyway. Require a barrier after polling is
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* cleared to order subsequent test of need_resched().
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*/
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clear_thread_flag(TIF_POLLING_NRFLAG);
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smp_mb();
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break;
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}
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}
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HMT_medium();
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clear_thread_flag(TIF_POLLING_NRFLAG);
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local_irq_disable();
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idle_loop_epilog(in_purr);
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return index;
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}
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static void check_and_cede_processor(void)
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{
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/*
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* Ensure our interrupt state is properly tracked,
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* also checks if no interrupt has occurred while we
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* were soft-disabled
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*/
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if (prep_irq_for_idle()) {
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cede_processor();
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#ifdef CONFIG_TRACE_IRQFLAGS
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/* Ensure that H_CEDE returns with IRQs on */
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if (WARN_ON(!(mfmsr() & MSR_EE)))
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__hard_irq_enable();
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#endif
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}
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}
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static int dedicated_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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idle_loop_prolog(&in_purr);
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get_lppaca()->donate_dedicated_cpu = 1;
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HMT_medium();
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check_and_cede_processor();
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local_irq_disable();
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get_lppaca()->donate_dedicated_cpu = 0;
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idle_loop_epilog(in_purr);
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return index;
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}
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static int shared_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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unsigned long in_purr;
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idle_loop_prolog(&in_purr);
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/*
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* Yield the processor to the hypervisor. We return if
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* an external interrupt occurs (which are driven prior
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* to returning here) or if a prod occurs from another
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* processor. When returning here, external interrupts
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* are enabled.
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*/
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check_and_cede_processor();
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local_irq_disable();
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idle_loop_epilog(in_purr);
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return index;
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}
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/*
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* States for dedicated partition case.
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*/
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static struct cpuidle_state dedicated_states[] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* CEDE */
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.name = "CEDE",
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.desc = "CEDE",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &dedicated_cede_loop },
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};
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/*
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* States for shared partition case.
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*/
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static struct cpuidle_state shared_states[] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* Shared Cede */
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.name = "Shared Cede",
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.desc = "Shared Cede",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &shared_cede_loop },
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};
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static int pseries_cpuidle_cpu_online(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_enable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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static int pseries_cpuidle_cpu_dead(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_disable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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/*
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* pseries_cpuidle_driver_init()
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*/
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static int pseries_cpuidle_driver_init(void)
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{
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int idle_state;
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struct cpuidle_driver *drv = &pseries_idle_driver;
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drv->state_count = 0;
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for (idle_state = 0; idle_state < max_idle_state; ++idle_state) {
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/* Is the state not enabled? */
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if (cpuidle_state_table[idle_state].enter == NULL)
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continue;
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drv->states[drv->state_count] = /* structure copy */
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cpuidle_state_table[idle_state];
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drv->state_count += 1;
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}
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return 0;
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}
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/*
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* pseries_idle_probe()
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* Choose state table for shared versus dedicated partition
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*/
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static int pseries_idle_probe(void)
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{
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if (cpuidle_disable != IDLE_NO_OVERRIDE)
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return -ENODEV;
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if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
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if (lppaca_shared_proc(get_lppaca())) {
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cpuidle_state_table = shared_states;
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max_idle_state = ARRAY_SIZE(shared_states);
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} else {
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cpuidle_state_table = dedicated_states;
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max_idle_state = ARRAY_SIZE(dedicated_states);
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}
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} else
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return -ENODEV;
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if (max_idle_state > 1) {
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snooze_timeout_en = true;
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snooze_timeout = cpuidle_state_table[1].target_residency *
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tb_ticks_per_usec;
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}
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return 0;
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}
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static int __init pseries_processor_idle_init(void)
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{
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int retval;
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retval = pseries_idle_probe();
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if (retval)
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return retval;
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pseries_cpuidle_driver_init();
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retval = cpuidle_register(&pseries_idle_driver, NULL);
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if (retval) {
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printk(KERN_DEBUG "Registration of pseries driver failed.\n");
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return retval;
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}
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retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
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"cpuidle/pseries:online",
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pseries_cpuidle_cpu_online, NULL);
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WARN_ON(retval < 0);
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retval = cpuhp_setup_state_nocalls(CPUHP_CPUIDLE_DEAD,
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"cpuidle/pseries:DEAD", NULL,
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pseries_cpuidle_cpu_dead);
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WARN_ON(retval < 0);
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printk(KERN_DEBUG "pseries_idle_driver registered\n");
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return 0;
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}
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device_initcall(pseries_processor_idle_init);
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