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Index: sys/kern/subr_epoch.c
===================================================================
--- sys/kern/subr_epoch.c
+++ sys/kern/subr_epoch.c
@@ -66,16 +66,18 @@
#define EPOCH_ALIGN CACHE_LINE_SIZE
#endif
-TAILQ_HEAD (epoch_tdlist, epoch_tracker);
+TAILQ_HEAD(epoch_tdlist, epoch_tracker);
typedef struct epoch_record {
ck_epoch_record_t er_record;
- struct epoch_context er_drain_ctx;
struct epoch *er_parent;
- volatile struct epoch_tdlist er_tdlist;
- volatile uint32_t er_gen;
+ struct epoch_tdlist er_tdlist;
+ struct thread *er_firsttd;
+ struct thread *er_blockedtd;
+ struct mtx er_lock;
+ struct lock_object er_lo;
uint32_t er_cpuid;
int er_drain_state;
-} __aligned(EPOCH_ALIGN) *epoch_record_t;
+} __aligned(EPOCH_ALIGN) *epoch_record_t;
#define EPOCH_DRAIN_START 2
#define EPOCH_DRAIN_RUNNING 1
@@ -91,8 +93,6 @@
const char *e_name;
};
-/* arbitrary --- needs benchmarking */
-#define MAX_ADAPTIVE_SPIN 100
#define MAX_EPOCHS 64
CTASSERT(sizeof(ck_epoch_entry_t) == sizeof(struct epoch_context));
@@ -101,33 +101,22 @@
SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW | CTLFLAG_MPSAFE, 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);
+static COUNTER_U64_DEFINE_EARLY(block_count);
+SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, blocked, CTLFLAG_RW,
+ &block_count,
+ "Number of times a thread was in an epoch when epoch_wait was called");
+static COUNTER_U64_DEFINE_EARLY(turnstile_count);
+SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, contended, CTLFLAG_RW,
+ &turnstile_count,
+ "Number of times a thread was blocked on a lock in an epoch during an epoch_wait");
+static COUNTER_U64_DEFINE_EARLY(call_count);
+SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, calls, CTLFLAG_RW,
+ &call_count,
+ "Number of times a callback was deferred");
+static COUNTER_U64_DEFINE_EARLY(call_task_count);
+SYSCTL_COUNTER_U64(_kern_epoch_stats, OID_AUTO, call_tasks, CTLFLAG_RW,
+ &call_task_count,
+ "Number of times a callback task was run");
CK_STACK_CONTAINER(struct ck_epoch_entry, stack_entry,
ck_epoch_entry_container)
@@ -186,7 +175,6 @@
va_list ap;
struct stackentry se, *new;
- stack_zero(&se.se_stack); /* XXX: is it really needed? */
stack_save(&se.se_stack);
/* Tree is never reduced - go lockless. */
@@ -265,13 +253,6 @@
{
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);
@@ -306,24 +287,39 @@
epoch_record_t er;
int cpu;
- epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK);
+ epoch->e_pcpu_record = uma_zalloc_pcpu(pcpu_zone_record, M_WAITOK |
+ M_ZERO);
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);
+ mtx_init(&er->er_lock, "epoch wait", NULL, MTX_DEF);
+ er->er_lo.lo_name = epoch->e_name;
+ TAILQ_INIT(&er->er_tdlist);
er->er_cpuid = cpu;
er->er_parent = epoch;
}
}
+/*
+ * Slow path for epoch_exit_preempt(): wake up blocked threads that have
+ * propagated their scheduling priority to us.
+ */
static void
-epoch_adjust_prio(struct thread *td, u_char prio)
+epoch_unblock(epoch_record_t er)
{
+ struct turnstile *ts;
- thread_lock(td);
- sched_prio(td, prio);
- thread_unlock(td);
+ KASSERT(er->er_blockedtd == curthread,
+ ("%s: unblocking from wrong thread", __func__));
+
+ mtx_lock(&er->er_lock);
+ turnstile_chain_lock(&er->er_lo);
+ ts = turnstile_lookup(&er->er_lo);
+ turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE);
+ turnstile_unpend(ts);
+ turnstile_chain_unlock(&er->er_lo);
+ er->er_blockedtd = NULL;
+ mtx_unlock(&er->er_lock);
}
epoch_t
@@ -391,9 +387,9 @@
THREAD_NO_SLEEPING();
critical_enter();
sched_pin();
- td->td_pre_epoch_prio = td->td_priority;
er = epoch_currecord(epoch);
TAILQ_INSERT_TAIL(&er->er_tdlist, et, et_link);
+ er->er_firsttd = TAILQ_FIRST(&er->er_tdlist)->et_td;
ck_epoch_begin(&er->er_record, &et->et_section);
critical_exit();
}
@@ -414,26 +410,27 @@
_epoch_exit_preempt(epoch_t epoch, epoch_tracker_t et EPOCH_FILE_LINE)
{
struct epoch_record *er;
+ struct epoch_tracker *fet;
struct thread *td;
INIT_CHECK(epoch);
td = curthread;
+ THREAD_SLEEPING_OK();
+
critical_enter();
sched_unpin();
- THREAD_SLEEPING_OK();
er = epoch_currecord(epoch);
+
MPASS(epoch->e_flags & EPOCH_PREEMPT);
- MPASS(et != NULL);
MPASS(et->et_td == td);
-#ifdef INVARIANTS
- et->et_td = (void*)0xDEADBEEF;
-#endif
+
ck_epoch_end(&er->er_record, &et->et_section);
TAILQ_REMOVE(&er->er_tdlist, et, et_link);
- er->er_gen++;
- if (__predict_false(td->td_pre_epoch_prio != td->td_priority))
- epoch_adjust_prio(td, td->td_pre_epoch_prio);
+ fet = TAILQ_FIRST(&er->er_tdlist);
+ er->er_firsttd = fet != NULL ? fet->et_td : NULL;
critical_exit();
+ if (__predict_false(er->er_blockedtd == td))
+ epoch_unblock(er);
#ifdef EPOCH_TRACE
epoch_trace_exit(td, epoch, et, file, line);
#endif
@@ -458,148 +455,61 @@
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_tracker *tdwait;
+ struct epoch_record *er;
+ struct thread *td;
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);
- /*
- * We lost a race and there's no longer any threads
- * on the CPU in an epoch section.
- */
- if (TAILQ_EMPTY(&record->er_tdlist))
- return;
- if (record->er_cpuid != curcpu) {
+ er = __containerof(cr, struct epoch_record, er_record);
+
+ td = er->er_firsttd;
+ if (td == NULL)
+ return;
+ if (TD_IS_RUNNING(td)) {
/*
- * 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
+ * There is nothing useful we can do until this thread exits the
+ * epoch.
*/
- gen = record->er_gen;
- thread_unlock(td);
+ cpu_spinwait();
+ return;
+ }
+
+ mtx_lock(&er->er_lock);
+ if (er->er_blockedtd == NULL) {
/*
- * We can't actually check if the waiting thread is running
- * so we simply poll for it to exit before giving up and
- * migrating.
+ * A thread in the target epoch is off-CPU. Prepare to make it
+ * the owner of this CPU's turnstile so that we can lend
+ * priority. Ensure that it will wake us up upon exiting the
+ * section, using the thread lock to ensure that it doesn't get
+ * scheduled and exit the section before we're ready.
*/
- do {
- cpu_spinwait();
- } while (!TAILQ_EMPTY(&record->er_tdlist) &&
- gen == record->er_gen &&
- spincount++ < MAX_ADAPTIVE_SPIN);
thread_lock(td);
- /*
- * If the generation has changed we can poll again
- * otherwise we need to migrate.
- */
- if (gen != record->er_gen)
+ if (TD_IS_RUNNING(td) || td != er->er_firsttd) {
+ thread_unlock(td);
+ mtx_unlock(&er->er_lock);
return;
+ }
+ er->er_blockedtd = td;
+ thread_unlock(td);
+ } else {
/*
- * 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.
+ * At least one other thread is blocked waiting for a thread to
+ * exit the target epoch. Join it.
*/
- return;
+ td = er->er_blockedtd;
}
- /*
- * 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 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);
+ ts = turnstile_trywait(&er->er_lo);
+ mtx_unlock(&er->er_lock);
- if (turnstile_lock(ts, &lock, &owner)) {
- if (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;
- }
- 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);
- /*
- * It is important the thread lock is dropped while yielding
- * to allow other threads to acquire the lock pointed to by
- * TDQ_LOCKPTR(td). Currently mi_switch() will unlock the
- * thread lock before returning. Else a deadlock like
- * situation might happen.
- */
- thread_lock(td);
+ counter_u64_add(turnstile_count, 1);
+ turnstile_wait(ts, td, TS_EXCLUSIVE_QUEUE);
}
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);
@@ -615,34 +525,10 @@
"of an epoch section of the same epoch"));
#endif
DROP_GIANT();
- thread_lock(td);
-
- 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));
@@ -731,8 +617,8 @@
*DPCPU_PTR(epoch_cb_count) -= total;
critical_exit();
- counter_u64_add(epoch_call_count, total);
- counter_u64_add(epoch_call_task_count, 1);
+ counter_u64_add(call_count, total);
+ counter_u64_add(call_task_count, 1);
head = ck_stack_batch_pop_npsc(&cb_stack);
for (cursor = head; cursor != NULL; cursor = next) {
Index: sys/kern/subr_turnstile.c
===================================================================
--- sys/kern/subr_turnstile.c
+++ sys/kern/subr_turnstile.c
@@ -590,41 +590,6 @@
return (ts);
}
-bool
-turnstile_lock(struct turnstile *ts, struct lock_object **lockp,
- struct thread **tdp)
-{
- struct turnstile_chain *tc;
- struct lock_object *lock;
-
- if ((lock = ts->ts_lockobj) == NULL)
- return (false);
- tc = TC_LOOKUP(lock);
- mtx_lock_spin(&tc->tc_lock);
- mtx_lock_spin(&ts->ts_lock);
- if (__predict_false(lock != ts->ts_lockobj)) {
- mtx_unlock_spin(&tc->tc_lock);
- mtx_unlock_spin(&ts->ts_lock);
- return (false);
- }
- *lockp = lock;
- *tdp = ts->ts_owner;
- return (true);
-}
-
-void
-turnstile_unlock(struct turnstile *ts, struct lock_object *lock)
-{
- struct turnstile_chain *tc;
-
- mtx_assert(&ts->ts_lock, MA_OWNED);
- mtx_unlock_spin(&ts->ts_lock);
- if (ts == curthread->td_turnstile)
- ts->ts_lockobj = NULL;
- tc = TC_LOOKUP(lock);
- mtx_unlock_spin(&tc->tc_lock);
-}
-
void
turnstile_assert(struct turnstile *ts)
{
Index: sys/sys/epoch.h
===================================================================
--- sys/sys/epoch.h
+++ sys/sys/epoch.h
@@ -61,7 +61,7 @@
const char *et_file;
int et_line;
#endif
-} __aligned(sizeof(void *));
+};
typedef struct epoch_tracker *epoch_tracker_t;
epoch_t epoch_alloc(const char *name, int flags);
Index: sys/sys/proc.h
===================================================================
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -316,7 +316,6 @@
u_char td_pri_class; /* (t) Scheduling class. */
u_char td_user_pri; /* (t) User pri from estcpu and nice. */
u_char td_base_user_pri; /* (t) Base user pri */
- u_char td_pre_epoch_prio; /* (k) User pri on entry to epoch */
uintptr_t td_rb_list; /* (k) Robust list head. */
uintptr_t td_rbp_list; /* (k) Robust priv list head. */
uintptr_t td_rb_inact; /* (k) Current in-action mutex loc. */
Index: sys/sys/turnstile.h
===================================================================
--- sys/sys/turnstile.h
+++ sys/sys/turnstile.h
@@ -99,9 +99,7 @@
struct turnstile *turnstile_trywait(struct lock_object *);
void turnstile_unpend(struct turnstile *);
void turnstile_wait(struct turnstile *, struct thread *, int);
-bool turnstile_lock(struct turnstile *, struct lock_object **,
- struct thread **);
-void turnstile_unlock(struct turnstile *, struct lock_object *);
void turnstile_assert(struct turnstile *);
+
#endif /* _KERNEL */
#endif /* _SYS_TURNSTILE_H_ */

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