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time.c

/******************************************************************************
 * 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"

DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);
DEFINE_PER_CPU(unsigned long, processed_stolen_time);
DEFINE_PER_CPU(unsigned long, processed_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(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(processed_blocked_time, cpu) = runstate->time[RUNSTATE_blocked];
      per_cpu(processed_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(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(processed_blocked_time, cpu)))
            blocked = 0;

      if (!time_after_eq(runstate.time[RUNSTATE_runnable] +
                     runstate.time[RUNSTATE_offline],
                     per_cpu(processed_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) {
                  write_seqlock(&xtime_lock);
                  do_timer(stolen + blocked);
                  local_cpu_data->itm_next = delta_itm + new_itm;
                  write_sequnlock(&xtime_lock);
            } else {
                  local_cpu_data->itm_next = delta_itm + new_itm;
            }
            per_cpu(processed_stolen_time, cpu) += NS_PER_TICK * stolen;
            per_cpu(processed_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);
}

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