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c6a37e8413
critical_enter() and critical_exit() are now solely a mechanism for deferring kernel preemptions. They no longer have any affect on interrupts. This means that standalone critical sections are now very cheap as they are simply unlocked integer increments and decrements for the common case. Spin mutexes now use a separate KPI implemented in MD code: spinlock_enter() and spinlock_exit(). This KPI is responsible for providing whatever MD guarantees are needed to ensure that a thread holding a spin lock won't be preempted by any other code that will try to lock the same lock. For now all archs continue to block interrupts in a "spinlock section" as they did formerly in all critical sections. Note that I've also taken this opportunity to push a few things into MD code rather than MI. For example, critical_fork_exit() no longer exists. Instead, MD code ensures that new threads have the correct state when they are created. Also, we no longer try to fixup the idlethreads for APs in MI code. Instead, each arch sets the initial curthread and adjusts the state of the idle thread it borrows in order to perform the initial context switch. This change is largely a big NOP, but the cleaner separation it provides will allow for more efficient alternative locking schemes in other parts of the kernel (bare critical sections rather than per-CPU spin mutexes for per-CPU data for example). Reviewed by: grehan, cognet, arch@, others Tested on: i386, alpha, sparc64, powerpc, arm, possibly more
128 lines
3.4 KiB
C
128 lines
3.4 KiB
C
/*-
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* Copyright (C) 2000-2004 The FreeBSD Project. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/kthread.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/resourcevar.h>
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#include <sys/sched.h>
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#include <sys/unistd.h>
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#ifdef SMP
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#include <sys/smp.h>
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#endif
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static void idle_setup(void *dummy);
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SYSINIT(idle_setup, SI_SUB_SCHED_IDLE, SI_ORDER_FIRST, idle_setup, NULL)
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static void idle_proc(void *dummy);
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/*
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* Set up per-cpu idle process contexts. The AP's shouldn't be running or
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* accessing their idle processes at this point, so don't bother with
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* locking.
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*/
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static void
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idle_setup(void *dummy)
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{
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#ifdef SMP
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struct pcpu *pc;
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#endif
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struct proc *p;
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struct thread *td;
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int error;
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#ifdef SMP
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SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
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error = kthread_create(idle_proc, NULL, &p,
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RFSTOPPED | RFHIGHPID, 0, "idle: cpu%d", pc->pc_cpuid);
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pc->pc_idlethread = FIRST_THREAD_IN_PROC(p);
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#else
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error = kthread_create(idle_proc, NULL, &p,
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RFSTOPPED | RFHIGHPID, 0, "idle");
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PCPU_SET(idlethread, FIRST_THREAD_IN_PROC(p));
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#endif
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if (error)
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panic("idle_setup: kthread_create error %d\n", error);
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PROC_LOCK(p);
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p->p_flag |= P_NOLOAD;
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mtx_lock_spin(&sched_lock);
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td = FIRST_THREAD_IN_PROC(p);
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TD_SET_CAN_RUN(td);
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td->td_flags |= TDF_IDLETD;
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sched_class(td->td_ksegrp, PRI_IDLE);
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sched_prio(td, PRI_MAX_IDLE);
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mtx_unlock_spin(&sched_lock);
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PROC_UNLOCK(p);
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#ifdef SMP
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}
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#endif
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}
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/*
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* The actual idle process.
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*/
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static void
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idle_proc(void *dummy)
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{
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struct proc *p;
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struct thread *td;
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#ifdef SMP
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cpumask_t mycpu;
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#endif
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td = curthread;
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p = td->td_proc;
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#ifdef SMP
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mycpu = PCPU_GET(cpumask);
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mtx_lock_spin(&sched_lock);
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idle_cpus_mask |= mycpu;
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mtx_unlock_spin(&sched_lock);
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#endif
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for (;;) {
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mtx_assert(&Giant, MA_NOTOWNED);
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while (sched_runnable() == 0)
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cpu_idle();
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mtx_lock_spin(&sched_lock);
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#ifdef SMP
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idle_cpus_mask &= ~mycpu;
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#endif
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mi_switch(SW_VOL, NULL);
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#ifdef SMP
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idle_cpus_mask |= mycpu;
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#endif
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mtx_unlock_spin(&sched_lock);
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}
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}
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