freebsd/sys/kern/subr_smp.c

/*
 * Copyright (c) 2001
 *	John Baldwin <jhb@FreeBSD.org>.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 4. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JOHN BALDWIN AND CONTRIBUTORS ``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 JOHN BALDWIN OR THE VOICES IN HIS HEAD
 * 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.
 */

/*
 * This module holds the global variables and machine independent functions
 * used for the kernel SMP support.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/proc.h>
#include <sys/bus.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/pcpu.h>
#include <sys/smp.h>
#include <sys/sysctl.h>

#include <machine/smp.h>

#include "opt_sched.h"

#ifdef SMP
volatile cpumask_t stopped_cpus;
volatile cpumask_t started_cpus;
cpumask_t idle_cpus_mask;
cpumask_t hlt_cpus_mask;
cpumask_t logical_cpus_mask;

void (*cpustop_restartfunc)(void);
#endif
/* amazingly enough this is used in non SMP code XXX BUG! */
cpumask_t all_cpus;

int mp_ncpus;
/* export this for libkvm consumers. */
int mp_maxcpus = MAXCPU;

struct cpu_top *smp_topology;
volatile int smp_started;
u_int mp_maxid;

SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");

SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD, &mp_maxcpus, 0,
    "Max number of CPUs that the system was compiled for.");

int smp_active = 0;	/* are the APs allowed to run? */
SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0,
    "Number of Auxillary Processors (APs) that were successfully started");

int smp_disabled = 0;	/* has smp been disabled? */
SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN, &smp_disabled, 0,
    "SMP has been disabled from the loader");
TUNABLE_INT("kern.smp.disabled", &smp_disabled);

int smp_cpus = 1;	/* how many cpu's running */
SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0,
    "Number of CPUs online");

#ifdef SMP
/* Enable forwarding of a signal to a process running on a different CPU */
static int forward_signal_enabled = 1;
SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
	   &forward_signal_enabled, 0,
	   "Forwarding of a signal to a process on a different CPU");

/* Enable forwarding of roundrobin to all other cpus */
static int forward_roundrobin_enabled = 1;
SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
	   &forward_roundrobin_enabled, 0,
	   "Forwarding of roundrobin to all other CPUs");

#ifdef SCHED_4BSD
/* Enable forwarding of wakeups to all other cpus */
SYSCTL_NODE(_kern_smp, OID_AUTO, ipiwakeup, CTLFLAG_RD, NULL, "Kernel SMP");

static int forward_wakeup_enabled = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, enabled, CTLFLAG_RW,
	   &forward_wakeup_enabled, 0,
	   "Forwarding of wakeup to idle CPUs");

static int forward_wakeups_requested = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, requested, CTLFLAG_RD,
	   &forward_wakeups_requested, 0,
	   "Requests for Forwarding of wakeup to idle CPUs");

static int forward_wakeups_delivered = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, delivered, CTLFLAG_RD,
	   &forward_wakeups_delivered, 0,
	   "Completed Forwarding of wakeup to idle CPUs");

static int forward_wakeup_use_mask = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, usemask, CTLFLAG_RW,
	   &forward_wakeup_use_mask, 0,
	   "Use the mask of idle cpus");

static int forward_wakeup_use_loop = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, useloop, CTLFLAG_RW,
	   &forward_wakeup_use_loop, 0,
	   "Use a loop to find idle cpus");

static int forward_wakeup_use_single = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, onecpu, CTLFLAG_RW,
	   &forward_wakeup_use_single, 0,
	   "Only signal one idle cpu");

static int forward_wakeup_use_htt = 0;
SYSCTL_INT(_kern_smp_ipiwakeup, OID_AUTO, htt2, CTLFLAG_RW,
	   &forward_wakeup_use_htt, 0,
	   "account for htt");

#endif /* SCHED_4BSD */
/* Variables needed for SMP rendezvous. */
static void (*smp_rv_setup_func)(void *arg);
static void (*smp_rv_action_func)(void *arg);
static void (*smp_rv_teardown_func)(void *arg);
static void *smp_rv_func_arg;
static volatile int smp_rv_waiters[2];

/* 
 * Shared mutex to restrict busywaits between smp_rendezvous() and
 * smp(_targeted)_tlb_shootdown().  A deadlock occurs if both of these
 * functions trigger at once and cause multiple CPUs to busywait with
 * interrupts disabled. 
 */
struct mtx smp_ipi_mtx;

/*
 * Let the MD SMP code initialize mp_maxid very early if it can.
 */
static void
mp_setmaxid(void *dummy)
{
	cpu_mp_setmaxid();
}
SYSINIT(cpu_mp_setmaxid, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_setmaxid, NULL)

/*
 * Call the MD SMP initialization code.
 */
static void
mp_start(void *dummy)
{

	/* Probe for MP hardware. */
	if (smp_disabled != 0 || cpu_mp_probe() == 0) {
		mp_ncpus = 1;
		all_cpus = PCPU_GET(cpumask);
		return;
	}

	mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);
	cpu_mp_start();
	printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
	    mp_ncpus);
	cpu_mp_announce();
}
SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_SECOND, mp_start, NULL)

void
forward_signal(struct thread *td)
{
	int id;

	/*
	 * signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
	 * this thread, so all we need to do is poke it if it is currently
	 * executing so that it executes ast().
	 */
	mtx_assert(&sched_lock, MA_OWNED);
	KASSERT(TD_IS_RUNNING(td),
	    ("forward_signal: thread is not TDS_RUNNING"));

	CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);

	if (!smp_started || cold || panicstr)
		return;
	if (!forward_signal_enabled)
		return;

	/* No need to IPI ourself. */
	if (td == curthread)
		return;

	id = td->td_oncpu;
	if (id == NOCPU)
		return;
	ipi_selected(1 << id, IPI_AST);
}

void
forward_roundrobin(void)
{
	struct pcpu *pc;
	struct thread *td;
	cpumask_t id, map, me;

	mtx_assert(&sched_lock, MA_OWNED);

	CTR0(KTR_SMP, "forward_roundrobin()");

	if (!smp_started || cold || panicstr)
		return;
	if (!forward_roundrobin_enabled)
		return;
	map = 0;
	me = PCPU_GET(cpumask);
	SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
		td = pc->pc_curthread;
		id = pc->pc_cpumask;
		if (id != me && (id & stopped_cpus) == 0 &&
		    td != pc->pc_idlethread) {
			td->td_flags |= TDF_NEEDRESCHED;
			map |= id;
		}
	}
	ipi_selected(map, IPI_AST);
}

#ifdef SCHED_4BSD
/* enable HTT_2 if you have a 2-way HTT cpu.*/
int
forward_wakeup(int  cpunum)
{
	cpumask_t map, me, dontuse;
	cpumask_t map2;
	struct pcpu *pc;
	cpumask_t id, map3;

	mtx_assert(&sched_lock, MA_OWNED);

	CTR0(KTR_SMP, "forward_wakeup()");

	if ((!forward_wakeup_enabled) ||
	     (forward_wakeup_use_mask == 0 && forward_wakeup_use_loop == 0))
		return (0);
	if (!smp_started || cold || panicstr)
		return (0);

	forward_wakeups_requested++;

/*
 * check the idle mask we received against what we calculated before
 * in the old version.
 */
	me = PCPU_GET(cpumask);
	/* 
	 * don't bother if we should be doing it ourself..
	 */
	if ((me & idle_cpus_mask) && (cpunum == NOCPU || me == (1 << cpunum)))
		return (0);

	dontuse = me | stopped_cpus | hlt_cpus_mask;
	map3 = 0;
	if (forward_wakeup_use_loop) {
		SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
			id = pc->pc_cpumask;
			if ( (id & dontuse) == 0 &&
			    pc->pc_curthread == pc->pc_idlethread) {
				map3 |= id;
			}
		}
	}

	if (forward_wakeup_use_mask) {
		map = 0;
		map = idle_cpus_mask & ~dontuse;

		/* If they are both on, compare and use loop if different */
		if (forward_wakeup_use_loop) {
			if (map != map3) {
				printf("map (%02X) != map3 (%02X)\n",
						map, map3);
				map = map3;
			}
		}
	} else {
		map = map3;
	}
	/* If we only allow a specific CPU, then mask off all the others */
	if (cpunum != NOCPU) {
		KASSERT((cpunum <= mp_maxcpus),("forward_wakeup: bad cpunum."));
		map &= (1 << cpunum);
	} else {
		/* Try choose an idle die. */
		if (forward_wakeup_use_htt) {
			map2 =  (map & (map >> 1)) & 0x5555;
			if (map2) {
				map = map2;
			}
		}

		/* set only one bit */ 
		if (forward_wakeup_use_single) {
			map = map & ((~map) + 1);
		}
	}
	if (map) {
		forward_wakeups_delivered++;
		ipi_selected(map, IPI_AST);
		return (1);
	}
	if (cpunum == NOCPU)
		printf("forward_wakeup: Idle processor not found\n");
	return (0);
}
#endif /* SCHED_4BSD */

/*
 * When called the executing CPU will send an IPI to all other CPUs
 *  requesting that they halt execution.
 *
 * Usually (but not necessarily) called with 'other_cpus' as its arg.
 *
 *  - Signals all CPUs in map to stop.
 *  - Waits for each to stop.
 *
 * Returns:
 *  -1: error
 *   0: NA
 *   1: ok
 *
 * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
 *            from executing at same time.
 */
int
stop_cpus(cpumask_t map)
{
	int i;

	if (!smp_started)
		return 0;

	CTR1(KTR_SMP, "stop_cpus(%x)", map);

	/* send the stop IPI to all CPUs in map */
	ipi_selected(map, IPI_STOP);

	i = 0;
	while ((atomic_load_acq_int(&stopped_cpus) & map) != map) {
		/* spin */
		i++;
#ifdef DIAGNOSTIC
		if (i == 100000) {
			printf("timeout stopping cpus\n");
			break;
		}
#endif
	}

	return 1;
}


/*
 * Called by a CPU to restart stopped CPUs. 
 *
 * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
 *
 *  - Signals all CPUs in map to restart.
 *  - Waits for each to restart.
 *
 * Returns:
 *  -1: error
 *   0: NA
 *   1: ok
 */
int
restart_cpus(cpumask_t map)
{

	if (!smp_started)
		return 0;

	CTR1(KTR_SMP, "restart_cpus(%x)", map);

	/* signal other cpus to restart */
	atomic_store_rel_int(&started_cpus, map);

	/* wait for each to clear its bit */
	while ((atomic_load_acq_int(&stopped_cpus) & map) != 0)
		;	/* nothing */

	return 1;
}

/*
 * All-CPU rendezvous.  CPUs are signalled, all execute the setup function 
 * (if specified), rendezvous, execute the action function (if specified),
 * rendezvous again, execute the teardown function (if specified), and then
 * resume.
 *
 * Note that the supplied external functions _must_ be reentrant and aware
 * that they are running in parallel and in an unknown lock context.
 */
void
smp_rendezvous_action(void)
{

	/* setup function */
	if (smp_rv_setup_func != NULL)
		smp_rv_setup_func(smp_rv_func_arg);
	/* spin on entry rendezvous */
	atomic_add_int(&smp_rv_waiters[0], 1);
	while (atomic_load_acq_int(&smp_rv_waiters[0]) < mp_ncpus)
		;	/* nothing */
	/* action function */
	if (smp_rv_action_func != NULL)
		smp_rv_action_func(smp_rv_func_arg);
	/* spin on exit rendezvous */
	atomic_add_int(&smp_rv_waiters[1], 1);
	while (atomic_load_acq_int(&smp_rv_waiters[1]) < mp_ncpus)
		;	/* nothing */
	/* teardown function */
	if (smp_rv_teardown_func != NULL)
		smp_rv_teardown_func(smp_rv_func_arg);
}

void
smp_rendezvous(void (* setup_func)(void *), 
	       void (* action_func)(void *),
	       void (* teardown_func)(void *),
	       void *arg)
{

	if (!smp_started) {
		if (setup_func != NULL)
			setup_func(arg);
		if (action_func != NULL)
			action_func(arg);
		if (teardown_func != NULL)
			teardown_func(arg);
		return;
	}
		
	/* obtain rendezvous lock */
	mtx_lock_spin(&smp_ipi_mtx);

	/* set static function pointers */
	smp_rv_setup_func = setup_func;
	smp_rv_action_func = action_func;
	smp_rv_teardown_func = teardown_func;
	smp_rv_func_arg = arg;
	smp_rv_waiters[0] = 0;
	smp_rv_waiters[1] = 0;

	/* signal other processors, which will enter the IPI with interrupts off */
	ipi_all_but_self(IPI_RENDEZVOUS);

	/* call executor function */
	smp_rendezvous_action();

	/* release lock */
	mtx_unlock_spin(&smp_ipi_mtx);
}
#else /* !SMP */

/*
 * Provide dummy SMP support for UP kernels.  Modules that need to use SMP
 * APIs will still work using this dummy support.
 */
static void
mp_setvariables_for_up(void *dummy)
{
	mp_ncpus = 1;
	mp_maxid = PCPU_GET(cpuid);
	all_cpus = PCPU_GET(cpumask);
	KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
}
SYSINIT(cpu_mp_setvariables, SI_SUB_TUNABLES, SI_ORDER_FIRST,
    mp_setvariables_for_up, NULL)

void
smp_rendezvous(void (* setup_func)(void *), 
	       void (* action_func)(void *),
	       void (* teardown_func)(void *),
	       void *arg)
{

	if (setup_func != NULL)
		setup_func(arg);
	if (action_func != NULL)
		action_func(arg);
	if (teardown_func != NULL)
		teardown_func(arg);
}
#endif /* SMP */