diff options
Diffstat (limited to 'sys/kern/kern_switch.c')
| -rw-r--r-- | sys/kern/kern_switch.c | 97 |
1 files changed, 93 insertions, 4 deletions
diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c index 464c6cf..d41974e 100644 --- a/sys/kern/kern_switch.c +++ b/sys/kern/kern_switch.c @@ -88,6 +88,8 @@ reassigned to keep this true. #include <sys/cdefs.h> __FBSDID("$FreeBSD$"); +#include "opt_full_preemption.h" + #include <sys/param.h> #include <sys/systm.h> #include <sys/kernel.h> @@ -423,10 +425,10 @@ setrunqueue(struct thread *td) } } -/************************************************************************ - * Critical section marker functions * - ************************************************************************/ -/* Critical sections that prevent preemption. */ +/* + * Kernel thread preemption implementation. Critical sections mark + * regions of code in which preemptions are not allowed. + */ void critical_enter(void) { @@ -447,6 +449,13 @@ critical_exit(void) KASSERT(td->td_critnest != 0, ("critical_exit: td_critnest == 0")); if (td->td_critnest == 1) { +#ifdef PREEMPTION + if (td->td_flags & TDF_OWEPREEMPT) { + mtx_lock_spin(&sched_lock); + mi_switch(SW_INVOL, NULL); + mtx_unlock_spin(&sched_lock); + } +#endif td->td_critnest = 0; cpu_critical_exit(); } else { @@ -454,6 +463,86 @@ critical_exit(void) } } +/* + * This function is called when a thread is about to be put on run queue + * because it has been made runnable or its priority has been adjusted. It + * determines if the new thread should be immediately preempted to. If so, + * it switches to it and eventually returns true. If not, it returns false + * so that the caller may place the thread on an appropriate run queue. + */ +int +maybe_preempt(struct thread *td) +{ + struct thread *ctd; + int cpri, pri; + + mtx_assert(&sched_lock, MA_OWNED); +#ifdef PREEMPTION + /* + * The new thread should not preempt the current thread if any of the + * following conditions are true: + * + * - The current thread has a higher (numerically lower) priority. + * - It is too early in the boot for context switches (cold is set). + * - The current thread has an inhibitor set or is in the process of + * exiting. In this case, the current thread is about to switch + * out anyways, so there's no point in preempting. If we did, + * the current thread would not be properly resumed as well, so + * just avoid that whole landmine. + * - If the new thread's priority is not a realtime priority and + * the current thread's priority is not an idle priority and + * FULL_PREEMPTION is disabled. + * + * If all of these conditions are false, but the current thread is in + * a nested critical section, then we have to defer the preemption + * until we exit the critical section. Otherwise, switch immediately + * to the new thread. + */ + ctd = curthread; + pri = td->td_priority; + cpri = ctd->td_priority; + if (pri >= cpri || cold /* || dumping */ || TD_IS_INHIBITED(ctd) || + td->td_kse->ke_state != KES_THREAD) + return (0); +#ifndef FULL_PREEMPTION + if (!(pri >= PRI_MIN_ITHD && pri <= PRI_MAX_ITHD) && + !(cpri >= PRI_MIN_IDLE)) + return (0); +#endif + if (ctd->td_critnest > 1) { + CTR1(KTR_PROC, "maybe_preempt: in critical section %d", + ctd->td_critnest); + ctd->td_flags |= TDF_OWEPREEMPT; + return (0); + } + + /* + * Our thread state says that we are already on a run queue, so + * update our state as if we had been dequeued by choosethread(). + */ + MPASS(TD_ON_RUNQ(td)); + TD_SET_RUNNING(td); + CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td, + td->td_proc->p_pid, td->td_proc->p_comm); + mi_switch(SW_INVOL, td); + return (1); +#else + return (0); +#endif +} + +#ifndef PREEMPTION +/* XXX: There should be a non-static version of this. */ +static void +printf_caddr_t(void *data) +{ + printf("%s", (char *)data); +} +static char preempt_warning[] = + "WARNING: Kernel preemption is disabled, expect reduced performance.\n"; +SYSINIT(preempt_warning, SI_SUB_COPYRIGHT, SI_ORDER_ANY, printf_caddr_t, + preempt_warning) +#endif /************************************************************************ * SYSTEM RUN QUEUE manipulations and tests * |
