![Vitaly Kuznetsov](/assets/img/avatar_default.png)
There is no particular reason to not enable TSC page clocksource on 32-bit. mul_u64_u64_shr() is available and despite the increased computational complexity (compared to 64bit) TSC page is still a huge win compared to MSR-based clocksource. In-kernel reads: MSR based clocksource: 3361 cycles TSC page clocksource: 49 cycles Reads from userspace (utilizing vDSO in case of TSC page): MSR based clocksource: 5664 cycles TSC page clocksource: 131 cycles Enabling TSC page on 32bits allows to get rid of CONFIG_HYPERV_TSCPAGE as it is now not any different from CONFIG_HYPERV_TIMER. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Michael Kelley <mikelley@microsoft.com> Link: https://lkml.kernel.org/r/20190822083630.17059-1-vkuznets@redhat.com
327 lines
8.3 KiB
C
327 lines
8.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Clocksource driver for the synthetic counter and timers
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* provided by the Hyper-V hypervisor to guest VMs, as described
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* in the Hyper-V Top Level Functional Spec (TLFS). This driver
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* is instruction set architecture independent.
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*
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* Copyright (C) 2019, Microsoft, Inc.
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*
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* Author: Michael Kelley <mikelley@microsoft.com>
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*/
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#include <linux/percpu.h>
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#include <linux/cpumask.h>
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#include <linux/clockchips.h>
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#include <linux/clocksource.h>
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#include <linux/sched_clock.h>
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#include <linux/mm.h>
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#include <clocksource/hyperv_timer.h>
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#include <asm/hyperv-tlfs.h>
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#include <asm/mshyperv.h>
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static struct clock_event_device __percpu *hv_clock_event;
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static u64 hv_sched_clock_offset __ro_after_init;
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/*
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* If false, we're using the old mechanism for stimer0 interrupts
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* where it sends a VMbus message when it expires. The old
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* mechanism is used when running on older versions of Hyper-V
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* that don't support Direct Mode. While Hyper-V provides
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* four stimer's per CPU, Linux uses only stimer0.
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*/
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static bool direct_mode_enabled;
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static int stimer0_irq;
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static int stimer0_vector;
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static int stimer0_message_sint;
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/*
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* ISR for when stimer0 is operating in Direct Mode. Direct Mode
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* does not use VMbus or any VMbus messages, so process here and not
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* in the VMbus driver code.
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*/
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void hv_stimer0_isr(void)
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{
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struct clock_event_device *ce;
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ce = this_cpu_ptr(hv_clock_event);
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ce->event_handler(ce);
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}
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EXPORT_SYMBOL_GPL(hv_stimer0_isr);
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static int hv_ce_set_next_event(unsigned long delta,
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struct clock_event_device *evt)
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{
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u64 current_tick;
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current_tick = hyperv_cs->read(NULL);
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current_tick += delta;
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hv_init_timer(0, current_tick);
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return 0;
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}
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static int hv_ce_shutdown(struct clock_event_device *evt)
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{
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hv_init_timer(0, 0);
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hv_init_timer_config(0, 0);
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if (direct_mode_enabled)
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hv_disable_stimer0_percpu_irq(stimer0_irq);
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return 0;
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}
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static int hv_ce_set_oneshot(struct clock_event_device *evt)
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{
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union hv_stimer_config timer_cfg;
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timer_cfg.as_uint64 = 0;
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timer_cfg.enable = 1;
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timer_cfg.auto_enable = 1;
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if (direct_mode_enabled) {
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/*
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* When it expires, the timer will directly interrupt
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* on the specified hardware vector/IRQ.
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*/
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timer_cfg.direct_mode = 1;
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timer_cfg.apic_vector = stimer0_vector;
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hv_enable_stimer0_percpu_irq(stimer0_irq);
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} else {
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/*
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* When it expires, the timer will generate a VMbus message,
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* to be handled by the normal VMbus interrupt handler.
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*/
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timer_cfg.direct_mode = 0;
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timer_cfg.sintx = stimer0_message_sint;
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}
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hv_init_timer_config(0, timer_cfg.as_uint64);
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return 0;
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}
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/*
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* hv_stimer_init - Per-cpu initialization of the clockevent
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*/
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void hv_stimer_init(unsigned int cpu)
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{
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struct clock_event_device *ce;
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/*
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* Synthetic timers are always available except on old versions of
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* Hyper-V on x86. In that case, just return as Linux will use a
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* clocksource based on emulated PIT or LAPIC timer hardware.
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*/
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if (!(ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE))
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return;
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ce = per_cpu_ptr(hv_clock_event, cpu);
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ce->name = "Hyper-V clockevent";
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ce->features = CLOCK_EVT_FEAT_ONESHOT;
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ce->cpumask = cpumask_of(cpu);
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ce->rating = 1000;
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ce->set_state_shutdown = hv_ce_shutdown;
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ce->set_state_oneshot = hv_ce_set_oneshot;
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ce->set_next_event = hv_ce_set_next_event;
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clockevents_config_and_register(ce,
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HV_CLOCK_HZ,
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HV_MIN_DELTA_TICKS,
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HV_MAX_MAX_DELTA_TICKS);
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}
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EXPORT_SYMBOL_GPL(hv_stimer_init);
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/*
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* hv_stimer_cleanup - Per-cpu cleanup of the clockevent
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*/
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void hv_stimer_cleanup(unsigned int cpu)
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{
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struct clock_event_device *ce;
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/* Turn off clockevent device */
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if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
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ce = per_cpu_ptr(hv_clock_event, cpu);
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hv_ce_shutdown(ce);
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}
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}
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EXPORT_SYMBOL_GPL(hv_stimer_cleanup);
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/* hv_stimer_alloc - Global initialization of the clockevent and stimer0 */
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int hv_stimer_alloc(int sint)
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{
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int ret;
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hv_clock_event = alloc_percpu(struct clock_event_device);
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if (!hv_clock_event)
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return -ENOMEM;
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direct_mode_enabled = ms_hyperv.misc_features &
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HV_STIMER_DIRECT_MODE_AVAILABLE;
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if (direct_mode_enabled) {
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ret = hv_setup_stimer0_irq(&stimer0_irq, &stimer0_vector,
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hv_stimer0_isr);
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if (ret) {
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free_percpu(hv_clock_event);
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hv_clock_event = NULL;
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return ret;
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}
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}
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stimer0_message_sint = sint;
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return 0;
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}
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EXPORT_SYMBOL_GPL(hv_stimer_alloc);
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/* hv_stimer_free - Free global resources allocated by hv_stimer_alloc() */
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void hv_stimer_free(void)
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{
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if (direct_mode_enabled && (stimer0_irq != 0)) {
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hv_remove_stimer0_irq(stimer0_irq);
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stimer0_irq = 0;
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}
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free_percpu(hv_clock_event);
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hv_clock_event = NULL;
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}
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EXPORT_SYMBOL_GPL(hv_stimer_free);
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/*
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* Do a global cleanup of clockevents for the cases of kexec and
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* vmbus exit
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*/
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void hv_stimer_global_cleanup(void)
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{
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int cpu;
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struct clock_event_device *ce;
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if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
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for_each_present_cpu(cpu) {
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ce = per_cpu_ptr(hv_clock_event, cpu);
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clockevents_unbind_device(ce, cpu);
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}
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}
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hv_stimer_free();
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}
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EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
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/*
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* Code and definitions for the Hyper-V clocksources. Two
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* clocksources are defined: one that reads the Hyper-V defined MSR, and
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* the other that uses the TSC reference page feature as defined in the
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* TLFS. The MSR version is for compatibility with old versions of
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* Hyper-V and 32-bit x86. The TSC reference page version is preferred.
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*/
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struct clocksource *hyperv_cs;
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EXPORT_SYMBOL_GPL(hyperv_cs);
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static struct ms_hyperv_tsc_page tsc_pg __aligned(PAGE_SIZE);
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struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
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{
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return &tsc_pg;
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}
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EXPORT_SYMBOL_GPL(hv_get_tsc_page);
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static u64 notrace read_hv_clock_tsc(struct clocksource *arg)
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{
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u64 current_tick = hv_read_tsc_page(&tsc_pg);
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if (current_tick == U64_MAX)
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hv_get_time_ref_count(current_tick);
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return current_tick;
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}
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static u64 read_hv_sched_clock_tsc(void)
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{
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return read_hv_clock_tsc(NULL) - hv_sched_clock_offset;
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}
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static struct clocksource hyperv_cs_tsc = {
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.name = "hyperv_clocksource_tsc_page",
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.rating = 400,
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.read = read_hv_clock_tsc,
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.mask = CLOCKSOURCE_MASK(64),
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.flags = CLOCK_SOURCE_IS_CONTINUOUS,
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};
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static u64 notrace read_hv_clock_msr(struct clocksource *arg)
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{
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u64 current_tick;
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/*
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* Read the partition counter to get the current tick count. This count
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* is set to 0 when the partition is created and is incremented in
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* 100 nanosecond units.
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*/
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hv_get_time_ref_count(current_tick);
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return current_tick;
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}
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static u64 read_hv_sched_clock_msr(void)
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{
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return read_hv_clock_msr(NULL) - hv_sched_clock_offset;
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}
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static struct clocksource hyperv_cs_msr = {
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.name = "hyperv_clocksource_msr",
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.rating = 400,
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.read = read_hv_clock_msr,
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.mask = CLOCKSOURCE_MASK(64),
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.flags = CLOCK_SOURCE_IS_CONTINUOUS,
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};
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static bool __init hv_init_tsc_clocksource(void)
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{
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u64 tsc_msr;
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phys_addr_t phys_addr;
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if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
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return false;
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hyperv_cs = &hyperv_cs_tsc;
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phys_addr = virt_to_phys(&tsc_pg);
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/*
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* The Hyper-V TLFS specifies to preserve the value of reserved
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* bits in registers. So read the existing value, preserve the
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* low order 12 bits, and add in the guest physical address
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* (which already has at least the low 12 bits set to zero since
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* it is page aligned). Also set the "enable" bit, which is bit 0.
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*/
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hv_get_reference_tsc(tsc_msr);
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tsc_msr &= GENMASK_ULL(11, 0);
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tsc_msr = tsc_msr | 0x1 | (u64)phys_addr;
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hv_set_reference_tsc(tsc_msr);
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hv_set_clocksource_vdso(hyperv_cs_tsc);
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clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
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hv_sched_clock_offset = hyperv_cs->read(hyperv_cs);
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hv_setup_sched_clock(read_hv_sched_clock_tsc);
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return true;
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}
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void __init hv_init_clocksource(void)
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{
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/*
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* Try to set up the TSC page clocksource. If it succeeds, we're
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* done. Otherwise, set up the MSR clocksoruce. At least one of
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* these will always be available except on very old versions of
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* Hyper-V on x86. In that case we won't have a Hyper-V
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* clocksource, but Linux will still run with a clocksource based
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* on the emulated PIT or LAPIC timer.
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*/
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if (hv_init_tsc_clocksource())
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return;
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if (!(ms_hyperv.features & HV_MSR_TIME_REF_COUNT_AVAILABLE))
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return;
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hyperv_cs = &hyperv_cs_msr;
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clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
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hv_sched_clock_offset = hyperv_cs->read(hyperv_cs);
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hv_setup_sched_clock(read_hv_sched_clock_msr);
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}
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EXPORT_SYMBOL_GPL(hv_init_clocksource);
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