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Annotation of OSKit-Mach/kern/ast.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Mach Operating System
        !             3:  * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University.
        !             4:  * Copyright (c) 1993,1994 The University of Utah and
        !             5:  * the Computer Systems Laboratory (CSL).
        !             6:  * All rights reserved.
        !             7:  *
        !             8:  * Permission to use, copy, modify and distribute this software and its
        !             9:  * documentation is hereby granted, provided that both the copyright
        !            10:  * notice and this permission notice appear in all copies of the
        !            11:  * software, derivative works or modified versions, and any portions
        !            12:  * thereof, and that both notices appear in supporting documentation.
        !            13:  *
        !            14:  * CARNEGIE MELLON, THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF
        !            15:  * THIS SOFTWARE IN ITS "AS IS" CONDITION, AND DISCLAIM ANY LIABILITY
        !            16:  * OF ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF
        !            17:  * THIS SOFTWARE.
        !            18:  *
        !            19:  * Carnegie Mellon requests users of this software to return to
        !            20:  *
        !            21:  *  Software Distribution Coordinator  or  [email protected]
        !            22:  *  School of Computer Science
        !            23:  *  Carnegie Mellon University
        !            24:  *  Pittsburgh PA 15213-3890
        !            25:  *
        !            26:  * any improvements or extensions that they make and grant Carnegie Mellon
        !            27:  * the rights to redistribute these changes.
        !            28:  */
        !            29: /*
        !            30:  *
        !            31:  *     This file contains routines to check whether an ast is needed.
        !            32:  *
        !            33:  *     ast_check() - check whether ast is needed for interrupt or context
        !            34:  *     switch.  Usually called by clock interrupt handler.
        !            35:  *
        !            36:  */
        !            37: 
        !            38: #include <cpus.h>
        !            39: #include <mach_fixpri.h>
        !            40: #include <norma_ipc.h>
        !            41: 
        !            42: #include <kern/ast.h>
        !            43: #include <kern/counters.h>
        !            44: #include "cpu_number.h"
        !            45: #include <kern/queue.h>
        !            46: #include <kern/sched.h>
        !            47: #include <kern/sched_prim.h>
        !            48: #include <kern/thread.h>
        !            49: #include <kern/processor.h>
        !            50: 
        !            51: #include <machine/machspl.h>   /* for splsched */
        !            52: 
        !            53: #if    MACH_FIXPRI
        !            54: #include <mach/policy.h>
        !            55: #endif /* MACH_FIXPRI */
        !            56: 
        !            57: 
        !            58: volatile ast_t need_ast[NCPUS];
        !            59: 
        !            60: void
        !            61: ast_init()
        !            62: {
        !            63: #ifndef        MACHINE_AST
        !            64:        register int i;
        !            65: 
        !            66:        for (i=0; i<NCPUS; i++)
        !            67:                need_ast[i] = 0;
        !            68: #endif /* MACHINE_AST */
        !            69: }
        !            70: 
        !            71: void
        !            72: ast_taken()
        !            73: {
        !            74:        register thread_t self = current_thread();
        !            75:        register ast_t reasons;
        !            76: 
        !            77:        /*
        !            78:         *      Interrupts are still disabled.
        !            79:         *      We must clear need_ast and then enable interrupts.
        !            80:         */
        !            81: 
        !            82:        reasons = need_ast[cpu_number()];
        !            83:        need_ast[cpu_number()] = AST_ZILCH;
        !            84:        (void) spl0();
        !            85: 
        !            86:        /*
        !            87:         *      These actions must not block.
        !            88:         */
        !            89: 
        !            90:        if (reasons & AST_NETWORK)
        !            91:                net_ast();
        !            92: 
        !            93: #if    NORMA_IPC
        !            94:        if (reasons & AST_NETIPC)
        !            95:                netipc_ast();
        !            96: #endif /* NORMA_IPC */
        !            97: 
        !            98:        /*
        !            99:         *      Make darn sure that we don't call thread_halt_self
        !           100:         *      or thread_block from the idle thread.
        !           101:         */
        !           102: 
        !           103:        if (self != current_processor()->idle_thread) {
        !           104: #ifndef MIGRATING_THREADS
        !           105:                while (thread_should_halt(self))
        !           106:                        thread_halt_self();
        !           107: #endif
        !           108: 
        !           109:                /*
        !           110:                 *      One of the previous actions might well have
        !           111:                 *      woken a high-priority thread, so we use
        !           112:                 *      csw_needed in addition to AST_BLOCK.
        !           113:                 */
        !           114: 
        !           115:                if ((reasons & AST_BLOCK) ||
        !           116:                    csw_needed(self, current_processor())) {
        !           117:                        counter(c_ast_taken_block++);
        !           118:                        thread_block(thread_exception_return);
        !           119:                }
        !           120:        }
        !           121: }
        !           122: 
        !           123: void
        !           124: ast_check()
        !           125: {
        !           126:        register int            mycpu = cpu_number();
        !           127:        register processor_t    myprocessor;
        !           128:        register thread_t       thread = current_thread();
        !           129:        register run_queue_t    rq;
        !           130:        spl_t                   s = splsched();
        !           131: 
        !           132:        /*
        !           133:         *      Check processor state for ast conditions.
        !           134:         */
        !           135:        myprocessor = cpu_to_processor(mycpu);
        !           136:        switch(myprocessor->state) {
        !           137:            case PROCESSOR_OFF_LINE:
        !           138:            case PROCESSOR_IDLE:
        !           139:            case PROCESSOR_DISPATCHING:
        !           140:                /*
        !           141:                 *      No ast.
        !           142:                 */
        !           143:                break;
        !           144: 
        !           145: #if    NCPUS > 1
        !           146:            case PROCESSOR_ASSIGN:
        !           147:            case PROCESSOR_SHUTDOWN:
        !           148:                /*
        !           149:                 *      Need ast to force action thread onto processor.
        !           150:                 *
        !           151:                 * XXX  Should check if action thread is already there.
        !           152:                 */
        !           153:                ast_on(mycpu, AST_BLOCK);
        !           154:                break;
        !           155: #endif /* NCPUS > 1 */
        !           156: 
        !           157:            case PROCESSOR_RUNNING:
        !           158: 
        !           159:                /*
        !           160:                 *      Propagate thread ast to processor.  If we already
        !           161:                 *      need an ast, don't look for more reasons.
        !           162:                 */
        !           163:                ast_propagate(thread, mycpu);
        !           164:                if (ast_needed(mycpu))
        !           165:                        break;
        !           166: 
        !           167:                /*
        !           168:                 *      Context switch check.  The csw_needed macro isn't
        !           169:                 *      used here because the rq->low hint may be wrong,
        !           170:                 *      and fixing it here avoids an extra ast.
        !           171:                 *      First check the easy cases.
        !           172:                 */
        !           173:                if (thread->state & TH_SUSP || myprocessor->runq.count > 0) {
        !           174:                        ast_on(mycpu, AST_BLOCK);
        !           175:                        break;
        !           176:                }
        !           177: 
        !           178:                /*
        !           179:                 *      Update lazy evaluated runq->low if only timesharing.
        !           180:                 */
        !           181: #if    MACH_FIXPRI
        !           182:                if (myprocessor->processor_set->policies & POLICY_FIXEDPRI) {
        !           183:                    if (csw_needed(thread,myprocessor)) {
        !           184:                        ast_on(mycpu, AST_BLOCK);
        !           185:                        break;
        !           186:                    }
        !           187:                    else {
        !           188:                        /*
        !           189:                         *      For fixed priority threads, set first_quantum
        !           190:                         *      so entire new quantum is used.
        !           191:                         */
        !           192:                        if (thread->policy == POLICY_FIXEDPRI)
        !           193:                            myprocessor->first_quantum = TRUE;
        !           194:                    }
        !           195:                }
        !           196:                else {
        !           197: #endif /* MACH_FIXPRI                   */
        !           198:                rq = &(myprocessor->processor_set->runq);
        !           199:                if (!(myprocessor->first_quantum) && (rq->count > 0)) {
        !           200:                    register queue_t    q;
        !           201:                    /*
        !           202:                     *  This is not the first quantum, and there may
        !           203:                     *  be something in the processor_set runq.
        !           204:                     *  Check whether low hint is accurate.
        !           205:                     */
        !           206:                    q = rq->runq + *(volatile int *)&rq->low;
        !           207:                    if (queue_empty(q)) {
        !           208:                        register int i;
        !           209: 
        !           210:                        /*
        !           211:                         *      Need to recheck and possibly update hint.
        !           212:                         */
        !           213:                        simple_lock(&rq->lock);
        !           214:                        q = rq->runq + rq->low;
        !           215:                        if (rq->count > 0) {
        !           216:                            for (i = rq->low; i < NRQS; i++) {
        !           217:                                if(!(queue_empty(q)))
        !           218:                                    break;
        !           219:                                q++;
        !           220:                            }
        !           221:                            rq->low = i;
        !           222:                        }
        !           223:                        simple_unlock(&rq->lock);
        !           224:                    }
        !           225: 
        !           226:                    if (rq->low <= thread->sched_pri) {
        !           227:                        ast_on(mycpu, AST_BLOCK);
        !           228:                        break;
        !           229:                    }
        !           230:                }
        !           231: #if    MACH_FIXPRI
        !           232:                }
        !           233: #endif /* MACH_FIXPRI */
        !           234:                break;
        !           235: 
        !           236:            default:
        !           237:                panic("ast_check: Bad processor state (cpu %d processor %08x) state: %d",
        !           238:                        mycpu, myprocessor, myprocessor->state);
        !           239:        }
        !           240: 
        !           241:        (void) splx(s);
        !           242: }

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