source: mainline/kernel/generic/src/time/clock.c@ 498ced1

/*
 * Copyright (c) 2001-2004 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup time
 * @{
 */

/**
 * @file
 * @brief High-level clock interrupt handler.
 *
 * This file contains the clock() function which is the source
 * of preemption. It is also responsible for executing expired
 * timeouts.
 *
 */

#include <time/clock.h>
#include <time/timeout.h>
#include <config.h>
#include <synch/spinlock.h>
#include <synch/waitq.h>
#include <halt.h>
#include <proc/scheduler.h>
#include <cpu.h>
#include <arch.h>
#include <adt/list.h>
#include <atomic.h>
#include <proc/thread.h>
#include <sysinfo/sysinfo.h>
#include <arch/barrier.h>
#include <mm/frame.h>
#include <ddi/ddi.h>
#include <arch/cycle.h>

/* Pointer to variable with uptime */
uptime_t *uptime;

/** Physical memory area of the real time clock */
static parea_t clock_parea;

/** Fragment of second
 *
 * For updating  seconds correctly.
 *
 */
static sysarg_t secfrag = 0;

/** Initialize realtime clock counter
 *
 * The applications (and sometimes kernel) need to access accurate
 * information about realtime data. We allocate 1 page with these
 * data and update it periodically.
 *
 */
void clock_counter_init(void)
{
        uintptr_t faddr = frame_alloc(1, FRAME_ATOMIC, 0);
        if (faddr == 0)
                panic("Cannot allocate page for clock.");

        uptime = (uptime_t *) PA2KA(faddr);

        uptime->seconds1 = 0;
        uptime->seconds2 = 0;
        uptime->useconds = 0;

        clock_parea.pbase = faddr;
        clock_parea.frames = 1;
        clock_parea.unpriv = true;
        clock_parea.mapped = false;
        ddi_parea_register(&clock_parea);

        /*
         * Prepare information for the userspace so that it can successfully
         * physmem_map() the clock_parea.
         *
         */
        sysinfo_set_item_val("clock.faddr", NULL, (sysarg_t) faddr);
}

/** Update public counters
 *
 * Update it only on first processor
 * TODO: Do we really need so many write barriers?
 *
 */
static void clock_update_counters(void)
{
        if (CPU->id == 0) {
                secfrag += 1000000 / HZ;
                if (secfrag >= 1000000) {
                        secfrag -= 1000000;
                        uptime->seconds1++;
                        write_barrier();
                        uptime->useconds = secfrag;
                        write_barrier();
                        uptime->seconds2 = uptime->seconds1;
                } else
                        uptime->useconds += 1000000 / HZ;
        }
}

static void cpu_update_accounting(void)
{
        irq_spinlock_lock(&CPU->lock, false);
        uint64_t now = get_cycle();
        CPU->busy_cycles += now - CPU->last_cycle;
        CPU->last_cycle = now;
        irq_spinlock_unlock(&CPU->lock, false);
}

/** Clock routine
 *
 * Clock routine executed from clock interrupt handler
 * (assuming interrupts_disable()'d). Runs expired timeouts
 * and preemptive scheduling.
 *
 */
void clock(void)
{
        size_t missed_clock_ticks = CPU->missed_clock_ticks;

        /* Account CPU usage */
        cpu_update_accounting();

        /*
         * To avoid lock ordering problems,
         * run all expired timeouts as you visit them.
         *
         */
        size_t i;
        for (i = 0; i <= missed_clock_ticks; i++) {
                /* Update counters and accounting */
                clock_update_counters();
                cpu_update_accounting();

                irq_spinlock_lock(&CPU->timeoutlock, false);

                link_t *cur;
                while ((cur = list_first(&CPU->timeout_active_list)) != NULL) {
                        timeout_t *timeout = list_get_instance(cur, timeout_t,
                            link);

                        irq_spinlock_lock(&timeout->lock, false);
                        if (timeout->ticks-- != 0) {
                                irq_spinlock_unlock(&timeout->lock, false);
                                break;
                        }

                        list_remove(cur);
                        timeout_handler_t handler = timeout->handler;
                        void *arg = timeout->arg;
                        timeout_reinitialize(timeout);

                        irq_spinlock_unlock(&timeout->lock, false);
                        irq_spinlock_unlock(&CPU->timeoutlock, false);

                        handler(arg);

                        irq_spinlock_lock(&CPU->timeoutlock, false);
                }

                irq_spinlock_unlock(&CPU->timeoutlock, false);
        }
        CPU->missed_clock_ticks = 0;

        /*
         * Do CPU usage accounting and find out whether to preempt THREAD.
         *
         */

        if (THREAD) {
                uint64_t ticks;

                irq_spinlock_lock(&CPU->lock, false);
                CPU->needs_relink += 1 + missed_clock_ticks;
                irq_spinlock_unlock(&CPU->lock, false);

                irq_spinlock_lock(&THREAD->lock, false);
                if ((ticks = THREAD->ticks)) {
                        if (ticks >= 1 + missed_clock_ticks)
                                THREAD->ticks -= 1 + missed_clock_ticks;
                        else
                                THREAD->ticks = 0;
                }
                irq_spinlock_unlock(&THREAD->lock, false);

                if (ticks == 0 && PREEMPTION_ENABLED) {
                        scheduler();
#ifdef CONFIG_UDEBUG
                        /*
                         * Give udebug chance to stop the thread
                         * before it begins executing userspace code.
                         */
                        istate_t *istate = THREAD->udebug.uspace_state;
                        if ((istate) && (istate_from_uspace(istate)))
                                udebug_before_thread_runs();
#endif
                }
        }
}

/** @}
 */