0c0b25ae91
than as one-off hacks in various other parts of the kernel: - Add a function maybe_preempt() that is called from sched_add() to determine if a thread about to be added to a run queue should be preempted to directly. If it is not safe to preempt or if the new thread does not have a high enough priority, then the function returns false and sched_add() adds the thread to the run queue. If the thread should be preempted to but the current thread is in a nested critical section, then the flag TDF_OWEPREEMPT is set and the thread is added to the run queue. Otherwise, mi_switch() is called immediately and the thread is never added to the run queue since it is switch to directly. When exiting an outermost critical section, if TDF_OWEPREEMPT is set, then clear it and call mi_switch() to perform the deferred preemption. - Remove explicit preemption from ithread_schedule() as calling setrunqueue() now does all the correct work. This also removes the do_switch argument from ithread_schedule(). - Do not use the manual preemption code in mtx_unlock if the architecture supports native preemption. - Don't call mi_switch() in a loop during shutdown to give ithreads a chance to run if the architecture supports native preemption since the ithreads will just preempt DELAY(). - Don't call mi_switch() from the page zeroing idle thread for architectures that support native preemption as it is unnecessary. - Native preemption is enabled on the same archs that supported ithread preemption, namely alpha, i386, and amd64. This change should largely be a NOP for the default case as committed except that we will do fewer context switches in a few cases and will avoid the run queues completely when preempting. Approved by: scottl (with his re@ hat)
191 lines
5.4 KiB
C
191 lines
5.4 KiB
C
/*-
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* Copyright (c) 1994 John Dyson
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* Copyright (c) 2001 Matt Dillon
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*
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* All Rights Reserved.
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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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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
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* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
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* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* from: @(#)vm_machdep.c 7.3 (Berkeley) 5/13/91
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* Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
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* from: FreeBSD: .../i386/vm_machdep.c,v 1.165 2001/07/04 23:27:04 dillon
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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/proc.h>
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#include <sys/resourcevar.h>
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#include <sys/vmmeter.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/sched.h>
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#include <sys/sysctl.h>
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#include <sys/kthread.h>
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#include <sys/unistd.h>
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#include <vm/vm.h>
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#include <vm/vm_page.h>
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SYSCTL_DECL(_vm_stats_misc);
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static int cnt_prezero;
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SYSCTL_INT(_vm_stats_misc, OID_AUTO, cnt_prezero, CTLFLAG_RD,
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&cnt_prezero, 0, "");
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static int idlezero_enable = 1;
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SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, "");
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TUNABLE_INT("vm.idlezero_enable", &idlezero_enable);
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static int idlezero_maxrun = 16;
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SYSCTL_INT(_vm, OID_AUTO, idlezero_maxrun, CTLFLAG_RW, &idlezero_maxrun, 0, "");
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TUNABLE_INT("vm.idlezero_maxrun", &idlezero_maxrun);
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/*
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* Implement the pre-zeroed page mechanism.
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*/
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#define ZIDLE_LO(v) ((v) * 2 / 3)
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#define ZIDLE_HI(v) ((v) * 4 / 5)
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static int zero_state;
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static int
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vm_page_zero_check(void)
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{
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if (!idlezero_enable)
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return (0);
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/*
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* Attempt to maintain approximately 1/2 of our free pages in a
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* PG_ZERO'd state. Add some hysteresis to (attempt to) avoid
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* generally zeroing a page when the system is near steady-state.
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* Otherwise we might get 'flutter' during disk I/O / IPC or
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* fast sleeps. We also do not want to be continuously zeroing
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* pages because doing so may flush our L1 and L2 caches too much.
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*/
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if (zero_state && vm_page_zero_count >= ZIDLE_LO(cnt.v_free_count))
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return (0);
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if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
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return (0);
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return (1);
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}
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static int
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vm_page_zero_idle(void)
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{
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static int free_rover;
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vm_page_t m;
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mtx_lock_spin(&vm_page_queue_free_mtx);
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zero_state = 0;
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m = vm_pageq_find(PQ_FREE, free_rover, FALSE);
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if (m != NULL && (m->flags & PG_ZERO) == 0) {
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vm_pageq_remove_nowakeup(m);
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mtx_unlock_spin(&vm_page_queue_free_mtx);
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pmap_zero_page_idle(m);
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mtx_lock_spin(&vm_page_queue_free_mtx);
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m->flags |= PG_ZERO;
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vm_pageq_enqueue(PQ_FREE + m->pc, m);
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++vm_page_zero_count;
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++cnt_prezero;
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if (vm_page_zero_count >= ZIDLE_HI(cnt.v_free_count))
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zero_state = 1;
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}
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free_rover = (free_rover + PQ_PRIME2) & PQ_L2_MASK;
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mtx_unlock_spin(&vm_page_queue_free_mtx);
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return (1);
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}
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/* Called by vm_page_free to hint that a new page is available. */
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void
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vm_page_zero_idle_wakeup(void)
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{
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if (idlezero_enable && vm_page_zero_check())
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wakeup(&zero_state);
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}
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static void
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vm_pagezero(void __unused *arg)
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{
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struct proc *p;
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struct rtprio rtp;
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struct thread *td;
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int pages, pri;
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td = curthread;
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p = td->td_proc;
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rtp.prio = RTP_PRIO_MAX;
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rtp.type = RTP_PRIO_IDLE;
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pages = 0;
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mtx_lock_spin(&sched_lock);
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rtp_to_pri(&rtp, td->td_ksegrp);
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pri = td->td_priority;
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mtx_unlock_spin(&sched_lock);
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for (;;) {
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if (vm_page_zero_check()) {
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pages += vm_page_zero_idle();
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#ifndef PREEMPTION
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if (pages > idlezero_maxrun || sched_runnable()) {
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mtx_lock_spin(&sched_lock);
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mi_switch(SW_VOL, NULL);
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mtx_unlock_spin(&sched_lock);
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pages = 0;
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}
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#endif
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} else {
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tsleep(&zero_state, pri, "pgzero", hz * 300);
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pages = 0;
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}
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}
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}
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static struct proc *pagezero_proc;
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static void
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pagezero_start(void __unused *arg)
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{
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int error;
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error = kthread_create(vm_pagezero, NULL, &pagezero_proc, RFSTOPPED, 0,
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"pagezero");
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if (error)
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panic("pagezero_start: error %d\n", error);
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/*
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* We're an idle task, don't count us in the load.
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*/
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PROC_LOCK(pagezero_proc);
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pagezero_proc->p_flag |= P_NOLOAD;
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PROC_UNLOCK(pagezero_proc);
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mtx_lock_spin(&sched_lock);
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setrunqueue(FIRST_THREAD_IN_PROC(pagezero_proc));
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mtx_unlock_spin(&sched_lock);
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}
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SYSINIT(pagezero, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, pagezero_start, NULL)
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