time.c

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/******************************************************************************
 * arch/ia64/xen/time.c
 *
 * Copyright (c) 2008 Isaku Yamahata <yamahata at valinux co jp>
 *                    VA Linux Systems Japan K.K.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <linux/delay.h>
#include <linux/kernel_stat.h>
#include <linux/posix-timers.h>
#include <linux/irq.h>
#include <linux/clocksource.h>

#include <asm/timex.h>

#include <asm/xen/hypervisor.h>

#include <xen/interface/vcpu.h>

#include "../kernel/fsyscall_gtod_data.h"

static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
static DEFINE_PER_CPU(unsigned long, xen_stolen_time);
static DEFINE_PER_CPU(unsigned long, xen_blocked_time);

/* taken from i386/kernel/time-xen.c */
static void xen_init_missing_ticks_accounting(int cpu)
{
    struct vcpu_register_runstate_memory_area area;
    struct vcpu_runstate_info *runstate = &per_cpu(xen_runstate, cpu);
    int rc;

    memset(runstate, 0, sizeof(*runstate));

    area.addr.v = runstate;
    rc = HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area, cpu,
                &area);
    WARN_ON(rc && rc != -ENOSYS);

    per_cpu(xen_blocked_time, cpu) = runstate->time[RUNSTATE_blocked];
    per_cpu(xen_stolen_time, cpu) = runstate->time[RUNSTATE_runnable]
                        + runstate->time[RUNSTATE_offline];
}

/*
 * Runstate accounting
 */
/* stolen from arch/x86/xen/time.c */
static void get_runstate_snapshot(struct vcpu_runstate_info *res)
{
    u64 state_time;
    struct vcpu_runstate_info *state;

    BUG_ON(preemptible());

    state = &__get_cpu_var(xen_runstate);

    /*
     * The runstate info is always updated by the hypervisor on
     * the current CPU, so there's no need to use anything
     * stronger than a compiler barrier when fetching it.
     */
    do {
        state_time = state->state_entry_time;
        rmb();
        *res = *state;
        rmb();
    } while (state->state_entry_time != state_time);
}

#define NS_PER_TICK (1000000000LL/HZ)

static unsigned long
consider_steal_time(unsigned long new_itm)
{
    unsigned long stolen, blocked;
    unsigned long delta_itm = 0, stolentick = 0;
    int cpu = smp_processor_id();
    struct vcpu_runstate_info runstate;
    struct task_struct *p = current;

    get_runstate_snapshot(&runstate);

    /*
     * Check for vcpu migration effect
     * In this case, itc value is reversed.
     * This causes huge stolen value.
     * This function just checks and reject this effect.
     */
    if (!time_after_eq(runstate.time[RUNSTATE_blocked],
               per_cpu(xen_blocked_time, cpu)))
        blocked = 0;

    if (!time_after_eq(runstate.time[RUNSTATE_runnable] +
               runstate.time[RUNSTATE_offline],
               per_cpu(xen_stolen_time, cpu)))
        stolen = 0;

    if (!time_after(delta_itm + new_itm, ia64_get_itc()))
        stolentick = ia64_get_itc() - new_itm;

    do_div(stolentick, NS_PER_TICK);
    stolentick++;

    do_div(stolen, NS_PER_TICK);

    if (stolen > stolentick)
        stolen = stolentick;

    stolentick -= stolen;
    do_div(blocked, NS_PER_TICK);

    if (blocked > stolentick)
        blocked = stolentick;

    if (stolen > 0 || blocked > 0) {
        account_steal_ticks(stolen);
        account_idle_ticks(blocked);
        run_local_timers();

        rcu_check_callbacks(cpu, user_mode(get_irq_regs()));

        scheduler_tick();
        run_posix_cpu_timers(p);
        delta_itm += local_cpu_data->itm_delta * (stolen + blocked);

        if (cpu == time_keeper_id)
            xtime_update(stolen + blocked);

        local_cpu_data->itm_next = delta_itm + new_itm;

        per_cpu(xen_stolen_time, cpu) += NS_PER_TICK * stolen;
        per_cpu(xen_blocked_time, cpu) += NS_PER_TICK * blocked;
    }
    return delta_itm;
}

static int xen_do_steal_accounting(unsigned long *new_itm)
{
    unsigned long delta_itm;
    delta_itm = consider_steal_time(*new_itm);
    *new_itm += delta_itm;
    if (time_after(*new_itm, ia64_get_itc()) && delta_itm)
        return 1;

    return 0;
}

static void xen_itc_jitter_data_reset(void)
{
    u64 lcycle, ret;

    do {
        lcycle = itc_jitter_data.itc_lastcycle;
        ret = cmpxchg(&itc_jitter_data.itc_lastcycle, lcycle, 0);
    } while (unlikely(ret != lcycle));
}

/* based on xen_sched_clock() in arch/x86/xen/time.c. */
/*
 * This relies on HAVE_UNSTABLE_SCHED_CLOCK. If it can't be defined,
 * something similar logic should be implemented here.
 */
/*
 * Xen sched_clock implementation.  Returns the number of unstolen
 * nanoseconds, which is nanoseconds the VCPU spent in RUNNING+BLOCKED
 * states.
 */
static unsigned long long xen_sched_clock(void)
{
    struct vcpu_runstate_info runstate;

    unsigned long long now;
    unsigned long long offset;
    unsigned long long ret;

    /*
     * Ideally sched_clock should be called on a per-cpu basis
     * anyway, so preempt should already be disabled, but that's
     * not current practice at the moment.
     */
    preempt_disable();

    /*
     * both ia64_native_sched_clock() and xen's runstate are
     * based on mAR.ITC. So difference of them makes sense.
     */
    now = ia64_native_sched_clock();

    get_runstate_snapshot(&runstate);

    WARN_ON(runstate.state != RUNSTATE_running);

    offset = 0;
    if (now > runstate.state_entry_time)
        offset = now - runstate.state_entry_time;
    ret = runstate.time[RUNSTATE_blocked] +
        runstate.time[RUNSTATE_running] +
        offset;

    preempt_enable();

    return ret;
}

struct pv_time_ops xen_time_ops __initdata = {
    .init_missing_ticks_accounting  = xen_init_missing_ticks_accounting,
    .do_steal_accounting        = xen_do_steal_accounting,
    .clocksource_resume     = xen_itc_jitter_data_reset,
    .sched_clock            = xen_sched_clock,
};

/* Called after suspend, to resume time.  */
static void xen_local_tick_resume(void)
{
    /* Just trigger a tick.  */
    ia64_cpu_local_tick();
    touch_softlockup_watchdog();
}

void
xen_timer_resume(void)
{
    unsigned int cpu;

    xen_local_tick_resume();

    for_each_online_cpu(cpu)
        xen_init_missing_ticks_accounting(cpu);
}

static void ia64_cpu_local_tick_fn(void *unused)
{
    xen_local_tick_resume();
    xen_init_missing_ticks_accounting(smp_processor_id());
}

void
xen_timer_resume_on_aps(void)
{
    smp_call_function(&ia64_cpu_local_tick_fn, NULL, 1);
}