/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2018, Matthew Macy <mmacy@freebsd.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/types.h>
#include <sys/systm.h>
#include <sys/counter.h>
#include <sys/epoch.h>
#include <sys/gtaskqueue.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/pcpu.h>
#include <sys/proc.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/turnstile.h>
#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/vm_kern.h>
#include <vm/uma.h>
#include <ck_epoch.h>
static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
/* arbitrary --- needs benchmarking */
#define MAX_ADAPTIVE_SPIN 1000
#define MAX_EPOCHS 64
CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information");
SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats");
/* Stats. */
static counter_u64_t block_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, nblocked, CTLFLAG_RW,
&block_count, "# of times a thread was in an epoch when epoch_wait was called");
static counter_u64_t migrate_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, migrations, CTLFLAG_RW,
&migrate_count, "# of times thread was migrated to another CPU in epoch_wait");
static counter_u64_t turnstile_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, ncontended, CTLFLAG_RW,
&turnstile_count, "# of times a thread was blocked on a lock in an epoch during an epoch_wait");
static counter_u64_t switch_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, switches, CTLFLAG_RW,
&switch_count, "# of times a thread voluntarily context switched in epoch_wait");
static counter_u64_t epoch_call_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_calls, CTLFLAG_RW,
&epoch_call_count, "# of times a callback was deferred");
static counter_u64_t epoch_call_task_count;
SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, epoch_call_tasks, CTLFLAG_RW,
&epoch_call_task_count, "# of times a callback task was run");
TAILQ_HEAD (threadlist, thread);
CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
ck_epoch_entry_container)
epoch_t allepochs[MAX_EPOCHS];
DPCPU_DEFINE(struct grouptask, epoch_cb_task);
DPCPU_DEFINE(int, epoch_cb_count);
static __read_mostly int inited;
static __read_mostly int epoch_count;
__read_mostly epoch_t global_epoch;
__read_mostly epoch_t global_epoch_preempt;
static void epoch_call_task(void *context __unused);
static uma_zone_t pcpu_zone_record;
static void
epoch_init(void *arg __unused)
{
int cpu;
block_count = counter_u64_alloc(M_WAITOK);
migrate_count = counter_u64_alloc(M_WAITOK);
turnstile_count = counter_u64_alloc(M_WAITOK);
switch_count = counter_u64_alloc(M_WAITOK);
epoch_call_count = counter_u64_alloc(M_WAITOK);
epoch_call_task_count = counter_u64_alloc(M_WAITOK);
pcpu_zone_record = uma_zcreate("epoch_record pcpu", sizeof(struct epoch_record),
NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_PCPU);
CPU_FOREACH(cpu) {
GROUPTASK_INIT(DPCPU_ID_PTR(cpu, epoch_cb_task), 0, epoch_call_task, NULL);
taskqgroup_attach_cpu(qgroup_softirq, DPCPU_ID_PTR(cpu, epoch_cb_task), NULL, cpu, -1, "epoch call task");
}
inited = 1;
global_epoch = epoch_alloc(0);
global_epoch_preempt = epoch_alloc(EPOCH_PREEMPT);
}
SYSINIT(epoch, SI_SUB_TASKQ + 1, SI_ORDER_FIRST, epoch_init, NULL);
#if !defined(EARLY_AP_STARTUP)
static void
epoch_init_smp(void *dummy __unused)
{
inited = 2;
}
SYSINIT(epoch_smp, SI_SUB_SMP + 1, SI_ORDER_FIRST, epoch_init_smp, NULL);
#endif
static void
epoch_ctor(epoch_t epoch)
{
epoch_record_t er;
int cpu;
epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
CPU_FOREACH(cpu) {
er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
bzero(er, sizeof(*er));
ck_epoch_register(&epoch->e_epoch, &er->er_record, NULL);
TAILQ_INIT((struct threadlist *)(uintptr_t)&er->er_tdlist);
er->er_cpuid = cpu;
}
}
epoch_t
epoch_alloc(int flags)
{
epoch_t epoch;
if (__predict_false(!inited))
panic("%s called too early in boot", __func__);
epoch = malloc(sizeof(struct epoch), M_EPOCH, M_ZERO | M_WAITOK);
ck_epoch_init(&epoch->e_epoch);
epoch_ctor(epoch);
MPASS(epoch_count < MAX_EPOCHS - 2);
epoch->e_flags = flags;
epoch->e_idx = epoch_count;
allepochs[epoch_count++] = epoch;
return (epoch);
}
void
epoch_free(epoch_t epoch)
{
#ifdef INVARIANTS
struct epoch_record *er;
int cpu;
CPU_FOREACH(cpu) {
er = zpcpu_get_cpu(epoch->e_pcpu_record, cpu);
MPASS(TAILQ_EMPTY(&er->er_tdlist));
}
#endif
allepochs[epoch->e_idx] = NULL;
epoch_wait(global_epoch);
uma_zfree_pcpu(pcpu_zone_record, epoch->e_pcpu_record);
free(epoch, M_EPOCH);
}
void
epoch_enter_preempt_KBI(epoch_t epoch, epoch_tracker_t et)
{
epoch_enter_preempt(epoch, et);
}
void
epoch_exit_preempt_KBI(epoch_t epoch, epoch_tracker_t et)
{
epoch_exit_preempt(epoch, et);
}
void
epoch_enter_KBI(epoch_t epoch)
{
epoch_enter(epoch);
}
void
epoch_exit_KBI(epoch_t epoch)
{
epoch_exit(epoch);
}
/*
* epoch_block_handler_preempt is a callback from the ck code when another thread is
* currently in an epoch section.
*/
static void
epoch_block_handler_preempt(struct ck_epoch *global __unused, ck_epoch_record_t *cr,
void *arg __unused)
{
epoch_record_t record;
struct thread *td, *owner, *curwaittd;
struct epoch_thread *tdwait;
struct turnstile *ts;
struct lock_object *lock;
int spincount, gen;
int locksheld __unused;
record = __containerof(cr, struct epoch_record, er_record);
td = curthread;
locksheld = td->td_locks;
spincount = 0;
counter_u64_add(block_count, 1);
if (record->er_cpuid != curcpu) {
/*
* If the head of the list is running, we can wait for it
* to remove itself from the list and thus save us the
* overhead of a migration
*/
if ((tdwait = TAILQ_FIRST(&record->er_tdlist)) != NULL &&
TD_IS_RUNNING(tdwait->et_td)) {
gen = record->er_gen;
thread_unlock(td);
do {
cpu_spinwait();
} while (tdwait == TAILQ_FIRST(&record->er_tdlist) &&
gen == record->er_gen && TD_IS_RUNNING(tdwait->et_td) &&
spincount++ < MAX_ADAPTIVE_SPIN);
thread_lock(td);
return;
}
/*
* Being on the same CPU as that of the record on which
* we need to wait allows us access to the thread
* list associated with that CPU. We can then examine the
* oldest thread in the queue and wait on its turnstile
* until it resumes and so on until a grace period
* elapses.
*
*/
counter_u64_add(migrate_count, 1);
sched_bind(td, record->er_cpuid);
/*
* At this point we need to return to the ck code
* to scan to see if a grace period has elapsed.
* We can't move on to check the thread list, because
* in the meantime new threads may have arrived that
* in fact belong to a different epoch.
*/
return;
}
/*
* Try to find a thread in an epoch section on this CPU
* waiting on a turnstile. Otherwise find the lowest
* priority thread (highest prio value) and drop our priority
* to match to allow it to run.
*/
TAILQ_FOREACH(tdwait, &record->er_tdlist, et_link) {
/*
* Propagate our priority to any other waiters to prevent us
* from starving them. They will have their original priority
* restore on exit from epoch_wait().
*/
curwaittd = tdwait->et_td;
if (!TD_IS_INHIBITED(curwaittd) && curwaittd->td_priority > td->td_priority) {
critical_enter();
thread_unlock(td);
thread_lock(curwaittd);
sched_prio(curwaittd, td->td_priority);
thread_unlock(curwaittd);
thread_lock(td);
critical_exit();
}
if (TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd) &&
((ts = curwaittd->td_blocked) != NULL)) {
/*
* We unlock td to allow turnstile_wait to reacquire the
* the thread lock. Before unlocking it we enter a critical
* section to prevent preemption after we reenable interrupts
* by dropping the thread lock in order to prevent curwaittd
* from getting to run.
*/
critical_enter();
thread_unlock(td);
owner = turnstile_lock(ts, &lock);
/*
* The owner pointer indicates that the lock succeeded. Only
* in case we hold the lock and the turnstile we locked is still
* the one that curwaittd is blocked on can we continue. Otherwise
* The turnstile pointer has been changed out from underneath
* us, as in the case where the lock holder has signalled curwaittd,
* and we need to continue.
*/
if (owner != NULL && ts == curwaittd->td_blocked) {
MPASS(TD_IS_INHIBITED(curwaittd) && TD_ON_LOCK(curwaittd));
critical_exit();
turnstile_wait(ts, owner, curwaittd->td_tsqueue);
counter_u64_add(turnstile_count, 1);
thread_lock(td);
return;
} else if (owner != NULL)
turnstile_unlock(ts, lock);
thread_lock(td);
critical_exit();
KASSERT(td->td_locks == locksheld,
("%d extra locks held", td->td_locks - locksheld));
}
}
/*
* We didn't find any threads actually blocked on a lock
* so we have nothing to do except context switch away.
*/
counter_u64_add(switch_count, 1);
mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
/*
* Release the thread lock while yielding to
* allow other threads to acquire the lock
* pointed to by TDQ_LOCKPTR(td). Else a
* deadlock like situation might happen. (HPS)
*/
thread_unlock(td);
thread_lock(td);
}
void
epoch_wait_preempt(epoch_t epoch)
{
struct thread *td;
int was_bound;
int old_cpu;
int old_pinned;
u_char old_prio;
int locks __unused;
MPASS(cold || epoch != NULL);
INIT_CHECK(epoch);
td = curthread;
#ifdef INVARIANTS
locks = curthread->td_locks;
MPASS(epoch->e_flags & EPOCH_PREEMPT);
if ((epoch->e_flags & EPOCH_LOCKED) == 0)
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
"epoch_wait() can be long running");
KASSERT(!in_epoch(epoch),
("epoch_wait_preempt() called in the middle "
"of an epoch section of the same epoch"));
#endif
thread_lock(td);
DROP_GIANT();
old_cpu = PCPU_GET(cpuid);
old_pinned = td->td_pinned;
old_prio = td->td_priority;
was_bound = sched_is_bound(td);
sched_unbind(td);
td->td_pinned = 0;
sched_bind(td, old_cpu);
ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler_preempt, NULL);
/* restore CPU binding, if any */
if (was_bound != 0) {
sched_bind(td, old_cpu);
} else {
/* get thread back to initial CPU, if any */
if (old_pinned != 0)
sched_bind(td, old_cpu);
sched_unbind(td);
}
/* restore pinned after bind */
td->td_pinned = old_pinned;
/* restore thread priority */
sched_prio(td, old_prio);
thread_unlock(td);
PICKUP_GIANT();
KASSERT(td->td_locks == locks,
("%d residual locks held", td->td_locks - locks));
}
static void
epoch_block_handler(struct ck_epoch *g __unused, ck_epoch_record_t *c __unused,
void *arg __unused)
{
cpu_spinwait();
}
void
epoch_wait(epoch_t epoch)
{
MPASS(cold || epoch != NULL);
INIT_CHECK(epoch);
MPASS(epoch->e_flags == 0);
critical_enter();
ck_epoch_synchronize_wait(&epoch->e_epoch, epoch_block_handler, NULL);
critical_exit();
}
void
epoch_call(epoch_t epoch, epoch_context_t ctx, void (*callback) (epoch_context_t))
{
epoch_record_t er;
ck_epoch_entry_t *cb;
cb = (void *)ctx;
MPASS(callback);
/* too early in boot to have epoch set up */
if (__predict_false(epoch == NULL))
goto boottime;
#if !defined(EARLY_AP_STARTUP)
if (__predict_false(inited < 2))
goto boottime;
#endif
critical_enter();
*DPCPU_PTR(epoch_cb_count) += 1;
er = epoch_currecord(epoch);
ck_epoch_call(&er->er_record, cb, (ck_epoch_cb_t *)callback);
critical_exit();
return;
boottime:
callback(ctx);
}
static void
epoch_call_task(void *arg __unused)
{
ck_stack_entry_t *cursor, *head, *next;
ck_epoch_record_t *record;
epoch_record_t er;
epoch_t epoch;
ck_stack_t cb_stack;
int i, npending, total;
ck_stack_init(&cb_stack);
critical_enter();
epoch_enter(global_epoch);
for (total = i = 0; i < epoch_count; i++) {
if (__predict_false((epoch = allepochs[i]) == NULL))
continue;
er = epoch_currecord(epoch);
record = &er->er_record;
if ((npending = record->n_pending) == 0)
continue;
ck_epoch_poll_deferred(record, &cb_stack);
total += npending - record->n_pending;
}
epoch_exit(global_epoch);
*DPCPU_PTR(epoch_cb_count) -= total;
critical_exit();
counter_u64_add(epoch_call_count, total);
counter_u64_add(epoch_call_task_count, 1);
head = ck_stack_batch_pop_npsc(&cb_stack);
for (cursor = head; cursor != NULL; cursor = next) {
struct ck_epoch_entry *entry =
ck_epoch_entry_container(cursor);
next = CK_STACK_NEXT(cursor);
entry->function(entry);
}
}
int
in_epoch_verbose(epoch_t epoch, int dump_onfail)
{
struct epoch_thread *tdwait;
struct thread *td;
epoch_record_t er;
td = curthread;
if (td->td_epochnest == 0)
return (0);
if (__predict_false((epoch) == NULL))
return (0);
critical_enter();
er = epoch_currecord(epoch);
TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
if (tdwait->et_td == td) {
critical_exit();
return (1);
}
#ifdef INVARIANTS
if (dump_onfail) {
MPASS(td->td_pinned);
printf("cpu: %d id: %d\n", curcpu, td->td_tid);
TAILQ_FOREACH(tdwait, &er->er_tdlist, et_link)
printf("td_tid: %d ", tdwait->et_td->td_tid);
printf("\n");
}
#endif
critical_exit();
return (0);
}
int
in_epoch(epoch_t epoch)
{
return (in_epoch_verbose(epoch, 0));
}
void
epoch_adjust_prio(struct thread *td, u_char prio)
{
thread_lock(td);
sched_prio(td, prio);
thread_unlock(td);
}
