syscall_subr.c   [plain text]

/*
 * Copyright (c) 2000-2004 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */

#include <mach/boolean.h>
#include <mach/thread_switch.h>
#include <ipc/ipc_port.h>
#include <ipc/ipc_space.h>
#include <kern/counters.h>
#include <kern/ipc_kobject.h>
#include <kern/processor.h>
#include <kern/sched.h>
#include <kern/sched_prim.h>
#include <kern/spl.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <mach/policy.h>

#include <kern/syscall_subr.h>
#include <mach/mach_host_server.h>
#include <mach/mach_syscalls.h>

/*
 *	swtch and swtch_pri both attempt to context switch (logic in
 *	thread_block no-ops the context switch if nothing would happen).
 *	A boolean is returned that indicates whether there is anything
 *	else runnable.
 *
 *	This boolean can be used by a thread waiting on a
 *	lock or condition:  If FALSE is returned, the thread is justified
 *	in becoming a resource hog by continuing to spin because there's
 *	nothing else useful that the processor could do.  If TRUE is
 *	returned, the thread should make one more check on the
 *	lock and then be a good citizen and really suspend.
 */

static void
swtch_continue(void)
{
	register processor_t	myprocessor;
    boolean_t				result;

    disable_preemption();
	myprocessor = current_processor();
	result =		myprocessor->runq.count > 0					||
				myprocessor->processor_set->runq.count > 0;
	enable_preemption();

	thread_syscall_return(result);
	/*NOTREACHED*/
}

boolean_t
swtch(
	__unused struct swtch_args *args)
{
	register processor_t	myprocessor;
	boolean_t				result;

	disable_preemption();
	myprocessor = current_processor();
	if (		myprocessor->runq.count == 0				&&
			myprocessor->processor_set->runq.count == 0			) {
		mp_enable_preemption();

		return (FALSE);
	}
	enable_preemption();

	counter(c_swtch_block++);

	thread_block_reason((thread_continue_t)swtch_continue, NULL, AST_YIELD);

	disable_preemption();
	myprocessor = current_processor();
	result =		myprocessor->runq.count > 0					||
				myprocessor->processor_set->runq.count > 0;
	enable_preemption();

	return (result);
}

static void
swtch_pri_continue(void)
{
	register processor_t	myprocessor;
    boolean_t				result;

	thread_depress_abort_internal(current_thread());

    disable_preemption();
	myprocessor = current_processor();
	result =		myprocessor->runq.count > 0					||
				myprocessor->processor_set->runq.count > 0;
	mp_enable_preemption();

	thread_syscall_return(result);
	/*NOTREACHED*/
}

boolean_t
swtch_pri(
__unused	struct swtch_pri_args *args)
{
	register processor_t	myprocessor;
	boolean_t				result;

	disable_preemption();
	myprocessor = current_processor();
	if (	myprocessor->runq.count == 0					&&
			myprocessor->processor_set->runq.count == 0			) {
		mp_enable_preemption();

		return (FALSE);
	}
	enable_preemption();

	counter(c_swtch_pri_block++);

	thread_depress_abstime(std_quantum);

	thread_block_reason((thread_continue_t)swtch_pri_continue, NULL, AST_YIELD);

	thread_depress_abort_internal(current_thread());

	disable_preemption();
	myprocessor = current_processor();
	result =	myprocessor->runq.count > 0						||
				myprocessor->processor_set->runq.count > 0;
	enable_preemption();

	return (result);
}

static void
thread_switch_continue(void)
{
	register thread_t	self = current_thread();
	int					option = self->saved.swtch.option;

	if (option == SWITCH_OPTION_DEPRESS)
		thread_depress_abort_internal(self);

	thread_syscall_return(KERN_SUCCESS);
	/*NOTREACHED*/
}

/*
 *	thread_switch:
 *
 *	Context switch.  User may supply thread hint.
 */
kern_return_t
thread_switch(
	struct thread_switch_args *args)
{
	register thread_t		thread, self = current_thread();
	mach_port_name_t		thread_name = args->thread_name;
	int						option = args->option;
	mach_msg_timeout_t		option_time = args->option_time;

    /*
     *	Process option.
     */
    switch (option) {

	case SWITCH_OPTION_NONE:
	case SWITCH_OPTION_DEPRESS:
	case SWITCH_OPTION_WAIT:
	    break;

	default:
	    return (KERN_INVALID_ARGUMENT);
    }

	/*
	 * Translate the port name if supplied.
	 */
    if (thread_name != MACH_PORT_NULL) {
		ipc_port_t			port;

		if (ipc_port_translate_send(self->task->itk_space,
									thread_name, &port) == KERN_SUCCESS) {
			ip_reference(port);
			ip_unlock(port);

			thread = convert_port_to_thread(port);
			ipc_port_release(port);

			if (thread == self) {
				thread_deallocate_internal(thread);
				thread = THREAD_NULL;
			}
		}
		else
			thread = THREAD_NULL;
	}
	else
		thread = THREAD_NULL;

	/*
	 * Try to handoff if supplied.
	 */
	if (thread != THREAD_NULL) {
		processor_t		processor;
		spl_t			s;

		s = splsched();
		thread_lock(thread);

		/*
		 *	Check if the thread is in the right pset,
		 *	is not bound to a different processor,
		 *	and that realtime is not involved.
		 *
		 *	Next, pull it off its run queue.  If it
		 *	doesn't come, it's not eligible.
		 */
		processor = current_processor();
		if (processor->current_pri < BASEPRI_RTQUEUES			&&
			thread->sched_pri < BASEPRI_RTQUEUES				&&
			thread->processor_set == processor->processor_set	&&
			(thread->bound_processor == PROCESSOR_NULL	||
			 thread->bound_processor == processor)				&&
			run_queue_remove(thread) != RUN_QUEUE_NULL			) {
			/*
			 *	Hah, got it!!
			 */
			thread_unlock(thread);

			thread_deallocate_internal(thread);

			if (option == SWITCH_OPTION_WAIT)
				assert_wait_timeout((event_t)assert_wait_timeout, THREAD_ABORTSAFE,
														option_time, 1000*NSEC_PER_USEC);
			else
			if (option == SWITCH_OPTION_DEPRESS)
				thread_depress_ms(option_time);

			self->saved.swtch.option = option;

			thread_run(self, (thread_continue_t)thread_switch_continue, NULL, thread);
			/* NOTREACHED */
		}

		thread_unlock(thread);
		splx(s);

		thread_deallocate(thread);
	}
		
	if (option == SWITCH_OPTION_WAIT)
		assert_wait_timeout((event_t)assert_wait_timeout, THREAD_ABORTSAFE, option_time, 1000*NSEC_PER_USEC);
	else
	if (option == SWITCH_OPTION_DEPRESS)
		thread_depress_ms(option_time);
	  
	self->saved.swtch.option = option;

	thread_block_reason((thread_continue_t)thread_switch_continue, NULL, AST_YIELD);

	if (option == SWITCH_OPTION_DEPRESS)
		thread_depress_abort_internal(self);

    return (KERN_SUCCESS);
}

/*
 * Depress thread's priority to lowest possible for the specified interval,
 * with a value of zero resulting in no timeout being scheduled.
 */
void
thread_depress_abstime(
	uint64_t				interval)
{
	register thread_t		self = current_thread();
	uint64_t				deadline;
    spl_t					s;

    s = splsched();
    thread_lock(self);
	if (!(self->sched_mode & TH_MODE_ISDEPRESSED)) {
		processor_t		myprocessor = self->last_processor;

		self->sched_pri = DEPRESSPRI;
		myprocessor->current_pri = self->sched_pri;
		self->sched_mode &= ~TH_MODE_PREEMPT;
		self->sched_mode |= TH_MODE_DEPRESS;

		if (interval != 0) {
			clock_absolutetime_interval_to_deadline(interval, &deadline);
			if (!timer_call_enter(&self->depress_timer, deadline))
				self->depress_timer_active++;
		}
	}
	thread_unlock(self);
    splx(s);
}

void
thread_depress_ms(
	mach_msg_timeout_t		interval)
{
	uint64_t		abstime;

	clock_interval_to_absolutetime_interval(
							interval, 1000*NSEC_PER_USEC, &abstime);
	thread_depress_abstime(abstime);
}

/*
 *	Priority depression expiration.
 */
void
thread_depress_expire(
	void			*p0,
	__unused void	*p1)
{
	thread_t		thread = p0;
    spl_t			s;

    s = splsched();
    thread_lock(thread);
	if (--thread->depress_timer_active == 0) {
		thread->sched_mode &= ~TH_MODE_ISDEPRESSED;
		compute_priority(thread, FALSE);
	}
    thread_unlock(thread);
    splx(s);
}

/*
 *	Prematurely abort priority depression if there is one.
 */
kern_return_t
thread_depress_abort_internal(
	thread_t				thread)
{
    kern_return_t 			result = KERN_NOT_DEPRESSED;
    spl_t					s;

    s = splsched();
    thread_lock(thread);
	if (!(thread->sched_mode & TH_MODE_POLLDEPRESS)) {
		if (thread->sched_mode & TH_MODE_ISDEPRESSED) {
			thread->sched_mode &= ~TH_MODE_ISDEPRESSED;
			compute_priority(thread, FALSE);
			result = KERN_SUCCESS;
		}

		if (timer_call_cancel(&thread->depress_timer))
			thread->depress_timer_active--;
	}
	thread_unlock(thread);
    splx(s);

    return (result);
}

void
thread_poll_yield(
	thread_t		self)
{
	spl_t			s;

	assert(self == current_thread());

	s = splsched();
	if (!(self->sched_mode & (TH_MODE_REALTIME|TH_MODE_TIMESHARE))) {
		uint64_t			total_computation, abstime;

		abstime = mach_absolute_time();
		total_computation = abstime - self->computation_epoch;
		total_computation += self->computation_metered;
		if (total_computation >= max_poll_computation) {
			processor_t		myprocessor = current_processor();
			ast_t			preempt;

			thread_lock(self);
			if (!(self->sched_mode & TH_MODE_ISDEPRESSED)) {
				self->sched_pri = DEPRESSPRI;
				myprocessor->current_pri = self->sched_pri;
				self->sched_mode &= ~TH_MODE_PREEMPT;
			}
			self->computation_epoch = abstime;
			self->computation_metered = 0;
			self->sched_mode |= TH_MODE_POLLDEPRESS;

			abstime += (total_computation >> sched_poll_yield_shift);
			if (!timer_call_enter(&self->depress_timer, abstime))
				self->depress_timer_active++;
			thread_unlock(self);

			if ((preempt = csw_check(self, myprocessor)) != AST_NONE)
				ast_on(preempt);
		}
	}
	splx(s);
}