* [lttng-dev] [RFC PATCH liburcu 1/2] Implement urcu workqueues internal API
2017-05-30 21:10 [lttng-dev] [RFC PATCH liburcu 0/2] Remove RCU requirements on hash table destroy Mathieu Desnoyers
@ 2017-05-30 21:10 ` Mathieu Desnoyers
2017-05-30 21:10 ` [lttng-dev] [RCU PATCH liburcu 2/2] Use workqueue in rculfhash Mathieu Desnoyers
1 sibling, 0 replies; 3+ messages in thread
From: Mathieu Desnoyers @ 2017-05-30 21:10 UTC (permalink / raw)
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
src/Makefile.am | 2 +-
src/workqueue.c | 507 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
src/workqueue.h | 104 ++++++++++++
3 files changed, 612 insertions(+), 1 deletion(-)
create mode 100644 src/workqueue.c
create mode 100644 src/workqueue.h
diff --git a/src/Makefile.am b/src/Makefile.am
index a801020..60b833d 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -54,7 +54,7 @@ liburcu_bp_la_SOURCES = urcu-bp.c urcu-pointer.c $(COMPAT)
liburcu_bp_la_LIBADD = liburcu-common.la
liburcu_cds_la_SOURCES = rculfqueue.c rculfstack.c lfstack.c \
- $(RCULFHASH) $(COMPAT)
+ workqueue.c workqueue.h $(RCULFHASH) $(COMPAT)
liburcu_cds_la_LIBADD = liburcu-common.la
pkgconfigdir = $(libdir)/pkgconfig
diff --git a/src/workqueue.c b/src/workqueue.c
new file mode 100644
index 0000000..891a8fc
--- /dev/null
+++ b/src/workqueue.c
@@ -0,0 +1,507 @@
+/*
+ * workqueue.c
+ *
+ * Userspace RCU library - Userspace workqeues
+ *
+ * Copyright (c) 2010 Paul E. McKenney <paulmck at linux.vnet.ibm.com>
+ * Copyright (c) 2017 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#define _LGPL_SOURCE
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <poll.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <sched.h>
+
+#include "compat-getcpu.h"
+#include "urcu/wfcqueue.h"
+#include "urcu-call-rcu.h"
+#include "urcu-pointer.h"
+#include "urcu/list.h"
+#include "urcu/futex.h"
+#include "urcu/tls-compat.h"
+#include "urcu/ref.h"
+#include "urcu-die.h"
+
+#include "workqueue.h"
+
+#define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
+#define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
+
+/* Data structure that identifies a workqueue. */
+
+struct urcu_workqueue {
+ /*
+ * We do not align head on a different cache-line than tail
+ * mainly because call_rcu callback-invocation threads use
+ * batching ("splice") to get an entire list of callbacks, which
+ * effectively empties the queue, and requires to touch the tail
+ * anyway.
+ */
+ struct cds_wfcq_tail cbs_tail;
+ struct cds_wfcq_head cbs_head;
+ unsigned long flags;
+ int32_t futex;
+ unsigned long qlen; /* maintained for debugging. */
+ pthread_t tid;
+ int cpu_affinity;
+ unsigned long loop_count;
+ void *priv;
+ void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv);
+ void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv);
+} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
+
+struct urcu_workqueue_completion {
+ int barrier_count;
+ int32_t futex;
+ struct urcu_ref ref;
+};
+
+struct urcu_workqueue_completion_work {
+ struct urcu_work work;
+ struct urcu_workqueue_completion *completion;
+};
+
+/*
+ * Periodically retry setting CPU affinity if we migrate.
+ * Losing affinity can be caused by CPU hotunplug/hotplug, or by
+ * cpuset(7).
+ */
+#if HAVE_SCHED_SETAFFINITY
+static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue)
+{
+ cpu_set_t mask;
+ int ret;
+
+ if (workqueue->cpu_affinity < 0)
+ return 0;
+ if (++workqueue->loop_count & SET_AFFINITY_CHECK_PERIOD_MASK)
+ return 0;
+ if (urcu_sched_getcpu() == workqueue->cpu_affinity)
+ return 0;
+
+ CPU_ZERO(&mask);
+ CPU_SET(workqueue->cpu_affinity, &mask);
+#if SCHED_SETAFFINITY_ARGS == 2
+ ret = sched_setaffinity(0, &mask);
+#else
+ ret = sched_setaffinity(0, sizeof(mask), &mask);
+#endif
+ /*
+ * EINVAL is fine: can be caused by hotunplugged CPUs, or by
+ * cpuset(7). This is why we should always retry if we detect
+ * migration.
+ */
+ if (ret && errno == EINVAL) {
+ ret = 0;
+ errno = 0;
+ }
+ return ret;
+}
+#else
+static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue)
+{
+ return 0;
+}
+#endif
+
+static void workqueue_wait(struct urcu_workqueue *workqueue)
+{
+ /* Read workqueue before read futex */
+ cmm_smp_mb();
+ if (uatomic_read(&workqueue->futex) != -1)
+ return;
+ while (futex_async(&workqueue->futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ return;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
+}
+
+static void workqueue_wake_up(struct urcu_workqueue *workqueue)
+{
+ /* Write to workqueue before reading/writing futex */
+ cmm_smp_mb();
+ if (caa_unlikely(uatomic_read(&workqueue->futex) == -1)) {
+ uatomic_set(&workqueue->futex, 0);
+ if (futex_async(&workqueue->futex, FUTEX_WAKE, 1,
+ NULL, NULL, 0) < 0)
+ urcu_die(errno);
+ }
+}
+
+static void __urcu_workqueue_wait_completion(struct urcu_workqueue_completion *completion)
+{
+ /* Read completion barrier count before read futex */
+ cmm_smp_mb();
+ if (uatomic_read(&completion->futex) != -1)
+ return;
+ while (futex_async(&completion->futex, FUTEX_WAIT, -1,
+ NULL, NULL, 0)) {
+ switch (errno) {
+ case EWOULDBLOCK:
+ /* Value already changed. */
+ return;
+ case EINTR:
+ /* Retry if interrupted by signal. */
+ break; /* Get out of switch. */
+ default:
+ /* Unexpected error. */
+ urcu_die(errno);
+ }
+ }
+}
+
+static void urcu_workqueue_completion_wake_up(struct urcu_workqueue_completion *completion)
+{
+ /* Write to completion barrier count before reading/writing futex */
+ cmm_smp_mb();
+ if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
+ uatomic_set(&completion->futex, 0);
+ if (futex_async(&completion->futex, FUTEX_WAKE, 1,
+ NULL, NULL, 0) < 0)
+ urcu_die(errno);
+ }
+}
+
+/* This is the code run by each worker thread. */
+
+static void *workqueue_thread(void *arg)
+{
+ unsigned long cbcount;
+ struct urcu_workqueue *workqueue = (struct urcu_workqueue *) arg;
+ int rt = !!(uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_RT);
+
+ if (set_thread_cpu_affinity(workqueue))
+ urcu_die(errno);
+
+ if (workqueue->initialize_worker_fct)
+ workqueue->initialize_worker_fct(workqueue, workqueue->priv);
+
+ if (!rt) {
+ uatomic_dec(&workqueue->futex);
+ /* Decrement futex before reading workqueue */
+ cmm_smp_mb();
+ }
+ for (;;) {
+ struct cds_wfcq_head cbs_tmp_head;
+ struct cds_wfcq_tail cbs_tmp_tail;
+ struct cds_wfcq_node *cbs, *cbs_tmp_n;
+ enum cds_wfcq_ret splice_ret;
+
+ if (set_thread_cpu_affinity(workqueue))
+ urcu_die(errno);
+
+ if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) {
+ /*
+ * Pause requested. Become quiescent: remove
+ * ourself from all global lists, and don't
+ * process any callback. The callback lists may
+ * still be non-empty though.
+ */
+ if (workqueue->worker_before_pause_fct)
+ workqueue->worker_before_pause_fct(workqueue, workqueue->priv);
+ cmm_smp_mb__before_uatomic_or();
+ uatomic_or(&workqueue->flags, URCU_WORKQUEUE_PAUSED);
+ while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSE) != 0)
+ (void) poll(NULL, 0, 1);
+ uatomic_and(&workqueue->flags, ~URCU_WORKQUEUE_PAUSED);
+ cmm_smp_mb__after_uatomic_and();
+ if (workqueue->worker_after_resume_fct)
+ workqueue->worker_after_resume_fct(workqueue, workqueue->priv);
+ }
+
+ cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
+ splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
+ &cbs_tmp_tail, &workqueue->cbs_head, &workqueue->cbs_tail);
+ assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
+ assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
+ if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
+ if (workqueue->grace_period_fct)
+ workqueue->grace_period_fct(workqueue, workqueue->priv);
+ cbcount = 0;
+ __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
+ &cbs_tmp_tail, cbs, cbs_tmp_n) {
+ struct rcu_head *rhp;
+
+ rhp = caa_container_of(cbs,
+ struct rcu_head, next);
+ rhp->func(rhp);
+ cbcount++;
+ }
+ uatomic_sub(&workqueue->qlen, cbcount);
+ }
+ if (uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_STOP)
+ break;
+ if (workqueue->worker_before_wait_fct)
+ workqueue->worker_before_wait_fct(workqueue, workqueue->priv);
+ if (!rt) {
+ if (cds_wfcq_empty(&workqueue->cbs_head,
+ &workqueue->cbs_tail)) {
+ workqueue_wait(workqueue);
+ (void) poll(NULL, 0, 10);
+ uatomic_dec(&workqueue->futex);
+ /*
+ * Decrement futex before reading
+ * call_rcu list.
+ */
+ cmm_smp_mb();
+ } else {
+ (void) poll(NULL, 0, 10);
+ }
+ } else {
+ (void) poll(NULL, 0, 10);
+ }
+ if (workqueue->worker_after_wake_up_fct)
+ workqueue->worker_after_wake_up_fct(workqueue, workqueue->priv);
+ }
+ if (!rt) {
+ /*
+ * Read call_rcu list before write futex.
+ */
+ cmm_smp_mb();
+ uatomic_set(&workqueue->futex, 0);
+ }
+ if (workqueue->finalize_worker_fct)
+ workqueue->finalize_worker_fct(workqueue, workqueue->priv);
+ return NULL;
+}
+
+struct urcu_workqueue *urcu_workqueue_create(unsigned long flags,
+ int cpu_affinity, void *priv,
+ void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv))
+{
+ struct urcu_workqueue *workqueue;
+ int ret;
+
+ workqueue = malloc(sizeof(*workqueue));
+ if (workqueue == NULL)
+ urcu_die(errno);
+ memset(workqueue, '\0', sizeof(*workqueue));
+ cds_wfcq_init(&workqueue->cbs_head, &workqueue->cbs_tail);
+ workqueue->qlen = 0;
+ workqueue->futex = 0;
+ workqueue->flags = flags;
+ workqueue->priv = priv;
+ workqueue->grace_period_fct = grace_period_fct;
+ workqueue->initialize_worker_fct = initialize_worker_fct;
+ workqueue->finalize_worker_fct = finalize_worker_fct;
+ workqueue->worker_before_wait_fct = worker_before_wait_fct;
+ workqueue->worker_after_wake_up_fct = worker_after_wake_up_fct;
+ workqueue->worker_before_pause_fct = worker_before_pause_fct;
+ workqueue->worker_after_resume_fct = worker_after_resume_fct;
+ workqueue->cpu_affinity = cpu_affinity;
+ workqueue->loop_count = 0;
+ cmm_smp_mb(); /* Structure initialized before pointer is planted. */
+ ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue);
+ if (ret) {
+ urcu_die(ret);
+ }
+ return workqueue;
+}
+
+static void wake_worker_thread(struct urcu_workqueue *workqueue)
+{
+ if (!(_CMM_LOAD_SHARED(workqueue->flags) & URCU_CALL_RCU_RT))
+ workqueue_wake_up(workqueue);
+}
+
+static int urcu_workqueue_destroy_worker(struct urcu_workqueue *workqueue)
+{
+ int ret;
+ void *retval;
+
+ uatomic_or(&workqueue->flags, URCU_WORKQUEUE_STOP);
+ wake_worker_thread(workqueue);
+
+ ret = pthread_join(workqueue->tid, &retval);
+ if (ret) {
+ urcu_die(ret);
+ }
+ if (retval != NULL) {
+ urcu_die(EINVAL);
+ }
+ workqueue->flags &= ~URCU_WORKQUEUE_STOP;
+ workqueue->tid = 0;
+ return 0;
+}
+
+void urcu_workqueue_destroy(struct urcu_workqueue *workqueue)
+{
+ if (workqueue == NULL) {
+ return;
+ }
+ if (urcu_workqueue_destroy_worker(workqueue)) {
+ urcu_die(errno);
+ }
+ assert(cds_wfcq_empty(&workqueue->cbs_head, &workqueue->cbs_tail));
+ free(workqueue);
+}
+
+void urcu_workqueue_queue_work(struct urcu_workqueue *workqueue,
+ struct urcu_work *work,
+ void (*func)(struct urcu_work *work))
+{
+ cds_wfcq_node_init(&work->next);
+ work->func = func;
+ cds_wfcq_enqueue(&workqueue->cbs_head, &workqueue->cbs_tail, &work->next);
+ uatomic_inc(&workqueue->qlen);
+ wake_worker_thread(workqueue);
+}
+
+static
+void free_completion(struct urcu_ref *ref)
+{
+ struct urcu_workqueue_completion *completion;
+
+ completion = caa_container_of(ref, struct urcu_workqueue_completion, ref);
+ free(completion);
+}
+
+static
+void _urcu_workqueue_wait_complete(struct urcu_work *work)
+{
+ struct urcu_workqueue_completion_work *completion_work;
+ struct urcu_workqueue_completion *completion;
+
+ completion_work = caa_container_of(work, struct urcu_workqueue_completion_work, work);
+ completion = completion_work->completion;
+ if (!uatomic_sub_return(&completion->barrier_count, 1))
+ urcu_workqueue_completion_wake_up(completion);
+ urcu_ref_put(&completion->ref, free_completion);
+ free(completion_work);
+}
+
+struct urcu_workqueue_completion *urcu_workqueue_create_completion(void)
+{
+ struct urcu_workqueue_completion *completion;
+
+ completion = calloc(sizeof(*completion), 1);
+ if (!completion)
+ urcu_die(errno);
+ urcu_ref_set(&completion->ref, 1);
+ completion->barrier_count = 0;
+ return completion;
+}
+
+void urcu_workqueue_destroy_completion(struct urcu_workqueue_completion *completion)
+{
+ urcu_ref_put(&completion->ref, free_completion);
+}
+
+void urcu_workqueue_wait_completion(struct urcu_workqueue_completion *completion)
+{
+ /* Wait for them */
+ for (;;) {
+ uatomic_dec(&completion->futex);
+ /* Decrement futex before reading barrier_count */
+ cmm_smp_mb();
+ if (!uatomic_read(&completion->barrier_count))
+ break;
+ __urcu_workqueue_wait_completion(completion);
+ }
+}
+
+void urcu_workqueue_queue_completion(struct urcu_workqueue *workqueue,
+ struct urcu_workqueue_completion *completion)
+{
+ struct urcu_workqueue_completion_work *work;
+
+ work = calloc(sizeof(*work), 1);
+ if (!work)
+ urcu_die(errno);
+ work->completion = completion;
+ urcu_ref_get(&completion->ref);
+ uatomic_inc(&completion->barrier_count);
+ urcu_workqueue_queue_work(workqueue, &work->work, _urcu_workqueue_wait_complete);
+}
+
+/*
+ * Wait for all in-flight work to complete execution.
+ */
+void urcu_workqueue_flush_queued_work(struct urcu_workqueue *workqueue)
+{
+ struct urcu_workqueue_completion *completion;
+
+ completion = urcu_workqueue_create_completion();
+ if (!completion)
+ urcu_die(ENOMEM);
+ urcu_workqueue_queue_completion(workqueue, completion);
+ urcu_workqueue_wait_completion(completion);
+ urcu_workqueue_destroy_completion(completion);
+}
+
+/* To be used in before fork handler. */
+void urcu_workqueue_pause_worker(struct urcu_workqueue *workqueue)
+{
+ uatomic_or(&workqueue->flags, URCU_WORKQUEUE_PAUSE);
+ cmm_smp_mb__after_uatomic_or();
+ wake_worker_thread(workqueue);
+
+ while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSED) == 0)
+ (void) poll(NULL, 0, 1);
+}
+
+/* To be used in after fork parent handler. */
+void urcu_workqueue_resume_worker(struct urcu_workqueue *workqueue)
+{
+ uatomic_and(&workqueue->flags, ~URCU_WORKQUEUE_PAUSE);
+ while ((uatomic_read(&workqueue->flags) & URCU_WORKQUEUE_PAUSED) != 0)
+ (void) poll(NULL, 0, 1);
+}
+
+void urcu_workqueue_create_worker(struct urcu_workqueue *workqueue)
+{
+ int ret;
+
+ /* Clear workqueue state from parent. */
+ workqueue->flags &= ~URCU_WORKQUEUE_PAUSED;
+ workqueue->flags &= ~URCU_WORKQUEUE_PAUSE;
+ workqueue->tid = 0;
+ ret = pthread_create(&workqueue->tid, NULL, workqueue_thread, workqueue);
+ if (ret) {
+ urcu_die(ret);
+ }
+}
diff --git a/src/workqueue.h b/src/workqueue.h
new file mode 100644
index 0000000..52b6973
--- /dev/null
+++ b/src/workqueue.h
@@ -0,0 +1,104 @@
+#ifndef _URCU_WORKQUEUE_H
+#define _URCU_WORKQUEUE_H
+
+/*
+ * workqueue.h
+ *
+ * Userspace RCU header - Userspace workqueues
+ *
+ * Copyright (c) 2009,2017 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
+ * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include <pthread.h>
+
+#include <urcu/wfcqueue.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Note that struct urcu_workqueue is opaque to callers. */
+
+struct urcu_workqueue;
+struct urcu_workqueue_completion;
+
+/* Flag values. */
+
+#define URCU_WORKQUEUE_RT (1U << 0)
+#define URCU_WORKQUEUE_STOP (1U << 1)
+#define URCU_WORKQUEUE_PAUSE (1U << 2)
+#define URCU_WORKQUEUE_PAUSED (1U << 3)
+
+/*
+ * The urcu_work data structure is placed in the structure to be acted
+ * upon via urcu_workqueue_queue_work().
+ */
+
+struct urcu_work {
+ struct cds_wfcq_node next;
+ void (*func)(struct urcu_work *head);
+};
+
+/*
+ * Exported functions
+ */
+
+struct urcu_workqueue *urcu_workqueue_create(unsigned long flags,
+ int cpu_affinity, void *priv,
+ void (*grace_period_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*initialize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*finalize_worker_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_before_wait_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_after_wake_up_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_before_pause_fct)(struct urcu_workqueue *workqueue, void *priv),
+ void (*worker_after_resume_fct)(struct urcu_workqueue *workqueue, void *priv));
+void urcu_workqueue_destroy(struct urcu_workqueue *workqueue);
+
+/*
+ * Never fails. Should not be used to enqueue work from worker threads
+ * after the application invokes urcu_workqueue_free.
+ */
+void urcu_workqueue_queue_work(struct urcu_workqueue *workqueue,
+ struct urcu_work *work,
+ void (*func)(struct urcu_work *work));
+
+struct urcu_workqueue_completion *urcu_workqueue_create_completion(void);
+void urcu_workqueue_destroy_completion(struct urcu_workqueue_completion *completion);
+
+void urcu_workqueue_queue_completion(struct urcu_workqueue *workqueue,
+ struct urcu_workqueue_completion *completion);
+void urcu_workqueue_wait_completion(struct urcu_workqueue_completion *completion);
+
+void urcu_workqueue_flush_queued_work(struct urcu_workqueue *workqueue);
+
+/*
+ * pause/resume/create worker threads. Can be used to pause worker
+ * threads across fork/clone while keeping the workqueue in place.
+ * Pause is used in parent pre-fork, resume in parent post-fork, create
+ * in child after-fork.
+ */
+void urcu_workqueue_pause_worker(struct urcu_workqueue *workqueue);
+void urcu_workqueue_resume_worker(struct urcu_workqueue *workqueue);
+void urcu_workqueue_create_worker(struct urcu_workqueue *workqueue);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_WORKQUEUE_H */
--
2.1.4
^ permalink raw reply [flat|nested] 3+ messages in thread* [lttng-dev] [RCU PATCH liburcu 2/2] Use workqueue in rculfhash
2017-05-30 21:10 [lttng-dev] [RFC PATCH liburcu 0/2] Remove RCU requirements on hash table destroy Mathieu Desnoyers
2017-05-30 21:10 ` [lttng-dev] [RFC PATCH liburcu 1/2] Implement urcu workqueues internal API Mathieu Desnoyers
@ 2017-05-30 21:10 ` Mathieu Desnoyers
1 sibling, 0 replies; 3+ messages in thread
From: Mathieu Desnoyers @ 2017-05-30 21:10 UTC (permalink / raw)
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
include/urcu/rculfhash.h | 15 ++++--
src/rculfhash-internal.h | 2 +-
src/rculfhash.c | 124 +++++++++++++++++++++++------------------------
3 files changed, 74 insertions(+), 67 deletions(-)
diff --git a/include/urcu/rculfhash.h b/include/urcu/rculfhash.h
index 9934422..0789aa5 100644
--- a/include/urcu/rculfhash.h
+++ b/include/urcu/rculfhash.h
@@ -176,10 +176,17 @@ struct cds_lfht *cds_lfht_new(unsigned long init_size,
* need to be informed of the value passed to cds_lfht_new().
*
* Return 0 on success, negative error value on error.
- * Threads calling this API need to be registered RCU read-side threads.
- * cds_lfht_destroy should *not* be called from a RCU read-side critical
- * section. It should *not* be called from a call_rcu thread context
- * neither.
+
+ * Prior to liburcu 0.10:
+ * - Threads calling this API need to be registered RCU read-side
+ * threads.
+ * - cds_lfht_destroy should *not* be called from a RCU read-side
+ * critical section. It should *not* be called from a call_rcu thread
+ * context neither.
+ *
+ * Starting from liburcu 0.10, rculfhash implements its own worker
+ * thread to handle resize operations, which removes RCU requirements on
+ * cds_lfht_destroy.
*/
extern
int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr);
diff --git a/src/rculfhash-internal.h b/src/rculfhash-internal.h
index d7cec95..0f8df97 100644
--- a/src/rculfhash-internal.h
+++ b/src/rculfhash-internal.h
@@ -82,7 +82,7 @@ struct cds_lfht {
*/
pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */
pthread_attr_t *resize_attr; /* Resize threads attributes */
- unsigned int in_progress_resize, in_progress_destroy;
+ unsigned int in_progress_destroy;
unsigned long resize_target;
int resize_initiated;
diff --git a/src/rculfhash.c b/src/rculfhash.c
index d7a1f23..b7b8f95 100644
--- a/src/rculfhash.c
+++ b/src/rculfhash.c
@@ -64,7 +64,7 @@
* - Split-counters are used to keep track of the number of
* nodes within the hash table for automatic resize triggering.
* - Resize operation initiated by long chain detection is executed by a
- * call_rcu thread, which keeps lock-freedom of add and remove.
+ * worker thread, which keeps lock-freedom of add and remove.
* - Resize operations are protected by a mutex.
* - The removal operation is split in two parts: first, a "removed"
* flag is set in the next pointer within the node to remove. Then,
@@ -276,6 +276,8 @@
#include <rculfhash-internal.h>
#include <stdio.h>
#include <pthread.h>
+#include "workqueue.h"
+#include "urcu-die.h"
/*
* Split-counters lazily update the global counter each 1024
@@ -335,11 +337,11 @@ struct ht_items_count {
} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
/*
- * rcu_resize_work: Contains arguments passed to RCU worker thread
+ * resize_work: Contains arguments passed to worker thread
* responsible for performing lazy resize.
*/
-struct rcu_resize_work {
- struct rcu_head head;
+struct resize_work {
+ struct urcu_work work;
struct cds_lfht *ht;
};
@@ -356,6 +358,8 @@ struct partition_resize_work {
unsigned long start, unsigned long len);
};
+static struct urcu_workqueue *cds_lfht_workqueue;
+
/*
* Algorithm to reverse bits in a word by lookup table, extended to
* 64-bit words.
@@ -1224,14 +1228,12 @@ void partition_resize_helper(struct cds_lfht *ht, unsigned long i,
if (start == 0 && nr_threads > 0)
return;
fallback:
- ht->flavor->thread_online();
fct(ht, i, start, len);
- ht->flavor->thread_offline();
}
/*
* Holding RCU read lock to protect _cds_lfht_add against memory
- * reclaim that could be performed by other call_rcu worker threads (ABA
+ * reclaim that could be performed by other worker threads (ABA
* problem).
*
* When we reach a certain length, we can split this population phase over
@@ -1308,7 +1310,7 @@ void init_table(struct cds_lfht *ht,
/*
* Holding RCU read lock to protect _cds_lfht_remove against memory
- * reclaim that could be performed by other call_rcu worker threads (ABA
+ * reclaim that could be performed by other worker threads (ABA
* problem).
* For a single level, we logically remove and garbage collect each node.
*
@@ -1320,8 +1322,9 @@ void init_table(struct cds_lfht *ht,
*
* Concurrent removal and add operations are helping us perform garbage
* collection of logically removed nodes. We guarantee that all logically
- * removed nodes have been garbage-collected (unlinked) before call_rcu is
- * invoked to free a hole level of bucket nodes (after a grace period).
+ * removed nodes have been garbage-collected (unlinked) before work
+ * enqueue is invoked to free a hole level of bucket nodes (after a
+ * grace period).
*
* Logical removal and garbage collection can therefore be done in batch
* or on a node-per-node basis, as long as the guarantee above holds.
@@ -1772,25 +1775,12 @@ int cds_lfht_delete_bucket(struct cds_lfht *ht)
*/
int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr)
{
- int ret, was_online;
+ int ret;
- /* Wait for in-flight resize operations to complete */
+ /* Cancel ongoing resize operations. */
_CMM_STORE_SHARED(ht->in_progress_destroy, 1);
- cmm_smp_mb(); /* Store destroy before load resize */
- was_online = ht->flavor->read_ongoing();
- if (was_online)
- ht->flavor->thread_offline();
- /* Calling with RCU read-side held is an error. */
- if (ht->flavor->read_ongoing()) {
- ret = -EINVAL;
- if (was_online)
- ht->flavor->thread_online();
- goto end;
- }
- while (uatomic_read(&ht->in_progress_resize))
- poll(NULL, 0, 100); /* wait for 100ms */
- if (was_online)
- ht->flavor->thread_online();
+ /* Wait for in-flight resize operations to complete */
+ urcu_workqueue_flush_queued_work(cds_lfht_workqueue);
ret = cds_lfht_delete_bucket(ht);
if (ret)
return ret;
@@ -1801,7 +1791,6 @@ int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr)
if (ret)
ret = -EBUSY;
poison_free(ht);
-end:
return ret;
}
@@ -1897,7 +1886,6 @@ void _do_cds_lfht_resize(struct cds_lfht *ht)
* Resize table, re-do if the target size has changed under us.
*/
do {
- assert(uatomic_read(&ht->in_progress_resize));
if (CMM_LOAD_SHARED(ht->in_progress_destroy))
break;
ht->resize_initiated = 1;
@@ -1930,71 +1918,47 @@ void resize_target_update_count(struct cds_lfht *ht,
void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size)
{
- int was_online;
-
- was_online = ht->flavor->read_ongoing();
- if (was_online)
- ht->flavor->thread_offline();
- /* Calling with RCU read-side held is an error. */
- if (ht->flavor->read_ongoing()) {
- static int print_once;
-
- if (!CMM_LOAD_SHARED(print_once))
- fprintf(stderr, "[error] rculfhash: cds_lfht_resize "
- "called with RCU read-side lock held.\n");
- CMM_STORE_SHARED(print_once, 1);
- assert(0);
- goto end;
- }
resize_target_update_count(ht, new_size);
CMM_STORE_SHARED(ht->resize_initiated, 1);
pthread_mutex_lock(&ht->resize_mutex);
_do_cds_lfht_resize(ht);
pthread_mutex_unlock(&ht->resize_mutex);
-end:
- if (was_online)
- ht->flavor->thread_online();
}
static
-void do_resize_cb(struct rcu_head *head)
+void do_resize_cb(struct urcu_work *work)
{
- struct rcu_resize_work *work =
- caa_container_of(head, struct rcu_resize_work, head);
- struct cds_lfht *ht = work->ht;
+ struct resize_work *resize_work =
+ caa_container_of(work, struct resize_work, work);
+ struct cds_lfht *ht = resize_work->ht;
- ht->flavor->thread_offline();
+ ht->flavor->register_thread();
pthread_mutex_lock(&ht->resize_mutex);
_do_cds_lfht_resize(ht);
pthread_mutex_unlock(&ht->resize_mutex);
- ht->flavor->thread_online();
+ ht->flavor->unregister_thread();
poison_free(work);
- cmm_smp_mb(); /* finish resize before decrement */
- uatomic_dec(&ht->in_progress_resize);
}
static
void __cds_lfht_resize_lazy_launch(struct cds_lfht *ht)
{
- struct rcu_resize_work *work;
+ struct resize_work *work;
/* Store resize_target before read resize_initiated */
cmm_smp_mb();
if (!CMM_LOAD_SHARED(ht->resize_initiated)) {
- uatomic_inc(&ht->in_progress_resize);
- cmm_smp_mb(); /* increment resize count before load destroy */
if (CMM_LOAD_SHARED(ht->in_progress_destroy)) {
- uatomic_dec(&ht->in_progress_resize);
return;
}
work = malloc(sizeof(*work));
if (work == NULL) {
dbg_printf("error allocating resize work, bailing out\n");
- uatomic_dec(&ht->in_progress_resize);
return;
}
work->ht = ht;
- ht->flavor->update_call_rcu(&work->head, do_resize_cb);
+ urcu_workqueue_queue_work(cds_lfht_workqueue,
+ &work->work, do_resize_cb);
CMM_STORE_SHARED(ht->resize_initiated, 1);
}
}
@@ -2045,3 +2009,39 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
}
__cds_lfht_resize_lazy_launch(ht);
}
+
+static void cds_lfht_fork_prepare(void)
+{
+ urcu_workqueue_pause_worker(cds_lfht_workqueue);
+}
+
+static void cds_lfht_fork_parent(void)
+{
+ urcu_workqueue_resume_worker(cds_lfht_workqueue);
+}
+
+static void cds_lfht_fork_child(void)
+{
+ urcu_workqueue_create_worker(cds_lfht_workqueue);
+}
+
+static void __attribute__((constructor)) cds_lfht_init_worker(void)
+{
+ int ret;
+
+ if (cds_lfht_workqueue)
+ return;
+ cds_lfht_workqueue = urcu_workqueue_create(0, -1, NULL,
+ NULL, NULL, NULL, NULL, NULL, NULL, NULL);
+ ret = pthread_atfork(cds_lfht_fork_prepare,
+ cds_lfht_fork_parent, cds_lfht_fork_child);
+ if (ret) {
+ urcu_die(ret);
+ }
+}
+
+static void __attribute__((destructor)) cds_lfht_fini_worker(void)
+{
+ urcu_workqueue_destroy(cds_lfht_workqueue);
+ cds_lfht_workqueue = NULL;
+}
--
2.1.4
^ permalink raw reply [flat|nested] 3+ messages in thread