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[Qemu-devel] [RFC PATCH] Introduce RCU-enabled DQs (v2)
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From: |
Mike Day |
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Subject: |
[Qemu-devel] [RFC PATCH] Introduce RCU-enabled DQs (v2) |
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Date: |
Sat, 24 Aug 2013 15:06:49 -0400 |
Add RCU-enabled variants on the existing bsd DQ facility. Each Q
operation has the same interface as the existing (non-RCU)
version. Also, each operation is implemented as macro for now.
Using the RCU-enabled DQ, existing DQ users will be able to convert to
RCU without using a different list interface.
This version (2) adds a macro to walk a Q in reverse:
QLIST_FOREACH_REVERSE_RCU(el, head, field)
Accordingly the reader threads in the test program walk the Q in
reverse in addition to walking forward.
To accompany the RCU-enabled DQ, there is also a test file that uses
concurrent readers to contend with a single updater.
This patchset builds on top of Paolo Bonzini's rcu tree:
https://github.com/bonzini/qemu/tree/rcu
Signed-off-by: Mike Day <address@hidden>
---
docs/rcu.txt | 2 +-
include/qemu/queue.h | 11 --
include/qemu/rcu_queue.h | 145 ++++++++++++++++++++++++
tests/Makefile | 6 +-
tests/rcuq_test.c | 290 +++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 440 insertions(+), 14 deletions(-)
create mode 100644 include/qemu/rcu_queue.h
create mode 100644 tests/rcuq_test.c
diff --git a/docs/rcu.txt b/docs/rcu.txt
index b3c593c..de59896 100644
--- a/docs/rcu.txt
+++ b/docs/rcu.txt
@@ -106,7 +106,7 @@ The core RCU API is small:
so that the reclaimer function can fetch the struct foo address
and free it:
- call_rcu1(foo_reclaim, &foo.rcu);
+ call_rcu1(&foo.rcu, foo_reclaim);
void foo_reclaim(struct rcu_head *rp)
{
diff --git a/include/qemu/queue.h b/include/qemu/queue.h
index 847ddd1..f6f0636 100644
--- a/include/qemu/queue.h
+++ b/include/qemu/queue.h
@@ -139,17 +139,6 @@ struct {
\
(elm)->field.le_prev = &(head)->lh_first; \
} while (/*CONSTCOND*/0)
-#define QLIST_INSERT_HEAD_RCU(head, elm, field) do { \
- (elm)->field.le_prev = &(head)->lh_first; \
- (elm)->field.le_next = (head)->lh_first; \
- smp_wmb(); /* fill elm before linking it */ \
- if ((head)->lh_first != NULL) { \
- (head)->lh_first->field.le_prev = &(elm)->field.le_next; \
- } \
- (head)->lh_first = (elm); \
- smp_wmb(); \
-} while (/* CONSTCOND*/0)
-
#define QLIST_REMOVE(elm, field) do { \
if ((elm)->field.le_next != NULL) \
(elm)->field.le_next->field.le_prev = \
diff --git a/include/qemu/rcu_queue.h b/include/qemu/rcu_queue.h
new file mode 100644
index 0000000..198a87d
--- /dev/null
+++ b/include/qemu/rcu_queue.h
@@ -0,0 +1,145 @@
+#ifndef QEMU_RCU_SYS_QUEUE_H
+#define QEMU_RCU_SYS_QUEUE_H
+
+/*
+ * rc_queue.h
+ *
+ * Userspace RCU QSBR header.
+ *
+ * LGPL-compatible code should include this header with :
+ *
+ * #define _LGPL_SOURCE
+ * #include <urcu.h>
+ *
+ * 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
+ *
+ * Copyright (c) 2013 Mike D. Day, IBM Corporation.
+ *
+ * IBM's contributions to this file may be relicensed under LGPLv2 or later.
+ */
+
+#include "qemu/rcu.h" /* rcu.h includes qemu/queue.h and qemu/atomic.h */
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * List functions.
+ */
+
+
+/*
+ * The difference between atomic_read/set and atomic_rcu_read/set
+ * is in the including of a read/write memory barrier to the volatile
+ * access. atomic_rcu_* macros include the memory barrier, the
+ * plain atomic macros do not. Therefore, it should be correct to
+ * issue a series of reads or writes to the same element using only
+ * the atomic_* macro, until the last read or write, which should be
+ * atomic_rcu_* to introduce a read or write memory barrier as
+ * appropriate.
+ */
+
+/* Upon publication of the listelm->next value, list readers
+ * will see the new node when following next pointers from
+ * antecedent nodes, but may not see the new node when following
+ * prev pointers from subsequent nodes until after the rcu grace
+ * period expires.
+ * see linux/include/rculist.h __list_add_rcu(new, prev, next)
+ */
+#define QLIST_INSERT_AFTER_RCU(listelm, elm, field) do { \
+ (elm)->field.le_next = (listelm)->field.le_next; \
+ (elm)->field.le_prev = &(listelm)->field.le_next; \
+ atomic_rcu_set(&(listelm)->field.le_next, (elm)); \
+ if ((elm)->field.le_next != NULL) { \
+ (elm)->field.le_next->field.le_prev = \
+ &(elm)->field.le_next; \
+ } \
+} while (/*CONSTCOND*/0)
+
+/* Upon publication of the listelm->prev->next value, list
+ * readers will see the new element when following prev pointers
+ * from subsequent elements, but may not see the new element
+ * when following next pointers from antecedent elements
+ * until after the rcu grace period expires.
+ */
+
+#define QLIST_INSERT_BEFORE_RCU(listelm, elm, field) do { \
+ (elm)->field.le_prev = (listelm)->field.le_prev; \
+ (elm)->field.le_next = (listelm); \
+ atomic_rcu_set((listelm)->field.le_prev, (elm)); \
+ (listelm)->field.le_prev = &(elm)->field.le_next; \
+} while (/*CONSTCOND*/0)
+
+
+/* Upon publication of the head->first value, list readers
+ * will see the new element when following the head, but may
+ * not see the new element when following prev pointers from
+ * subsequent elements until after the rcu grace period has
+ * expired.
+ */
+
+#define QLIST_INSERT_HEAD_RCU(head, elm, field) do { \
+ (elm)->field.le_prev = &(head)->lh_first; \
+ (elm)->field.le_next = (head)->lh_first; \
+ atomic_rcu_set((&(head)->lh_first), (elm)); \
+ if ((elm)->field.le_next != NULL) { \
+ (elm)->field.le_next->field.le_prev = \
+ &(elm)->field.le_next; \
+ } \
+} while (/*CONSTCOND*/0)
+
+
+/* prior to publication of the elm->prev->next value, some list
+ * readers may still see the removed element when following
+ * the antecedent's next pointer.
+ */
+
+#define QLIST_REMOVE_RCU(elm, field) do { \
+ if ((elm)->field.le_next != NULL) { \
+ (elm)->field.le_next->field.le_prev = \
+ (elm)->field.le_prev; \
+ } \
+ atomic_rcu_set((elm)->field.le_prev, (elm)->field.le_next); \
+} while (/*CONSTCOND*/0)
+
+/* list traversal must occur within an rcu critical section.
+ */
+
+#define QLIST_FOREACH_RCU(var, head, field) \
+ for ((var) = atomic_rcu_read(&(head)->lh_first); \
+ (var); \
+ (var) = ((var)->field.le_next))
+
+/* list traversal must occur within an rcu critical section.
+ */
+#define QLIST_FOREACH_SAFE_RCU(var, head, field, next_var) \
+ for ((var) = (atomic_rcu_read(&(head)->lh_first)); \
+ (var) && ((next_var) = (var)->field.le_next, 1); \
+ (var) = (next_var))
+
+/* QLIST_ENTRY MUST be the first element of (var)
+ */
+#define QLIST_FOREACH_REVERSE_RCU(var, head, field) \
+ for ( ; \
+ (var) && (var) != (head)->lh_first; \
+ (var) = (typeof(var))atomic_rcu_read(&(var)->field.le_prev))
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* QEMU_RCU_SYS_QUEUE.H */
diff --git a/tests/Makefile b/tests/Makefile
index 136b7a4..98674f9 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -53,7 +53,8 @@ gcov-files-test-int128-y =
check-unit-y += tests/test-bitops$(EXESUF)
check-unit-y += tests/rcutorture$(EXESUF)
gcov-files-rcutorture-y = util/rcu.c
-
+check-unit-y += tests/rcuq_test$(EXESUF)
+gcov-files-rcuq_test-y = util/rcu.c
check-block-$(CONFIG_POSIX) += tests/qemu-iotests-quick.sh
# All QTests for now are POSIX-only, but the dependencies are
@@ -105,7 +106,7 @@ test-obj-y = tests/check-qint.o tests/check-qstring.o
tests/check-qdict.o \
tests/test-qmp-input-visitor.o tests/test-qmp-input-strict.o \
tests/test-qmp-commands.o tests/test-visitor-serialization.o \
tests/test-x86-cpuid.o tests/test-mul64.o tests/test-int128.o \
- tests/test-tls.o tests/rcutorture.o
+ tests/test-tls.o tests/rcutorture.o tests/rcuq_test.o
test-qapi-obj-y = tests/test-qapi-visit.o tests/test-qapi-types.o
@@ -131,6 +132,7 @@ tests/test-cutils$(EXESUF): tests/test-cutils.o
util/cutils.o
tests/test-int128$(EXESUF): tests/test-int128.o
tests/test-tls$(EXESUF): tests/test-tls.o libqemuutil.a
tests/rcutorture$(EXESUF): tests/rcutorture.o libqemuutil.a
+tests/rcuq_test$(EXESUF): tests/rcuq_test.o libqemuutil.a
tests/test-qapi-types.c tests/test-qapi-types.h :\
$(SRC_PATH)/tests/qapi-schema/qapi-schema-test.json
$(SRC_PATH)/scripts/qapi-types.py
diff --git a/tests/rcuq_test.c b/tests/rcuq_test.c
new file mode 100644
index 0000000..4f62143
--- /dev/null
+++ b/tests/rcuq_test.c
@@ -0,0 +1,290 @@
+/*
+ * rcuq_test.c
+ *
+ * usage: rcuq_test <readers> <duration>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (c) 2013 Mike D. Day, IBM Corporation.
+ */
+
+/*
+ * Test variables.
+ */
+
+#include <glib.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include "qemu/atomic.h"
+#include "qemu/rcu.h"
+#include "qemu/compiler.h"
+#include "qemu/thread.h"
+#include "qemu/rcu_queue.h"
+
+long long n_reads = 0LL;
+long long n_updates = 0LL;
+long long n_reclaims = 0LL;
+long long n_nodes_removed = 0LL;
+long long n_nodes = 0LL;
+
+
+int nthreadsrunning;
+
+char argsbuf[64];
+
+#define GOFLAG_INIT 0
+#define GOFLAG_RUN 1
+#define GOFLAG_STOP 2
+
+static volatile int goflag = GOFLAG_INIT;
+
+#define RCU_READ_RUN 1000
+#define RCU_UPDATE_RUN 10
+#define NR_THREADS 100
+#define RCU_Q_LEN 100
+
+static QemuThread threads[NR_THREADS];
+static struct rcu_reader_data *data[NR_THREADS];
+static int n_threads;
+
+static int select_random_el(int max)
+{
+ return (rand() % max);
+}
+
+
+static void create_thread(void *(*func)(void *))
+{
+ if (n_threads >= NR_THREADS) {
+ fprintf(stderr, "Thread limit of %d exceeded!\n", NR_THREADS);
+ exit(-1);
+ }
+ qemu_thread_create(&threads[n_threads], func, &data[n_threads],
+ QEMU_THREAD_JOINABLE);
+ n_threads++;
+}
+
+static void wait_all_threads(void)
+{
+ int i;
+
+ for (i = 0; i < n_threads; i++) {
+ qemu_thread_join(&threads[i]);
+ }
+ n_threads = 0;
+}
+
+
+struct list_element {
+ QLIST_ENTRY(list_element) entry;
+ struct rcu_head rcu;
+ long long val;
+};
+
+static void reclaim_list_el(struct rcu_head *prcu)
+{
+ struct list_element *el = container_of(prcu, struct list_element, rcu);
+ g_free(el);
+ atomic_add(&n_reclaims, 1);
+}
+
+static QLIST_HEAD(q_list_head, list_element) Q_list_head;
+
+static void *rcu_q_reader(void *arg)
+{
+ long long j, n_reads_local = 0;
+ struct list_element *el, *prev_el = NULL;
+
+ *(struct rcu_reader_data **)arg = tls_get_rcu_reader();
+ atomic_inc(&nthreadsrunning);
+ rcu_thread_offline();
+ while (goflag == GOFLAG_INIT) {
+ g_usleep(1000);
+ }
+
+ rcu_thread_online();
+ while (goflag == GOFLAG_RUN) {
+ rcu_read_lock();
+ QLIST_FOREACH_RCU(el, &Q_list_head, entry) {
+ prev_el = el;
+ j = el->val;
+ if (j){;}
+ n_reads_local++;
+ if (goflag == GOFLAG_STOP)
+ break;
+ }
+ rcu_read_unlock();
+
+ rcu_quiescent_state();
+ g_usleep(100);
+ rcu_read_lock();
+ QLIST_FOREACH_REVERSE_RCU(prev_el, &Q_list_head, entry) {
+ el = prev_el;
+ j = el->val;
+ if (j){;}
+ n_reads_local++;
+ if (goflag != GOFLAG_RUN)
+ break;
+ }
+ rcu_read_unlock();
+
+ rcu_quiescent_state();
+ g_usleep(100);
+ }
+ rcu_thread_offline();
+ atomic_add(&n_reads, n_reads_local);
+ return NULL;
+}
+
+
+static void *rcu_q_updater(void *arg)
+{
+ int i, j, target_el;
+ long long n_updates_local = 0;
+ long long n_removed_local = 0;
+ struct list_element *el, *prev_el;
+
+ *(struct rcu_reader_data **)arg = tls_get_rcu_reader();
+ atomic_inc(&nthreadsrunning);
+ while (goflag == GOFLAG_INIT) {
+ g_usleep(1000);
+ }
+
+ while (goflag == GOFLAG_RUN) {
+ for (i = 0; i < RCU_UPDATE_RUN && goflag == GOFLAG_RUN; i++) {
+ target_el = select_random_el(RCU_Q_LEN);
+ j = 0;
+ /* FOREACH_RCU could work here but let's use both macros */
+ QLIST_FOREACH_SAFE_RCU(prev_el, &Q_list_head, entry, el) {
+ j++;
+ if (target_el == j) {
+ QLIST_REMOVE_RCU(prev_el, entry);
+ /* may be more than one updater in the future */
+ call_rcu1(&prev_el->rcu, reclaim_list_el);
+ n_removed_local++;
+ break;
+ }
+ }
+ if (goflag == GOFLAG_STOP)
+ break;
+ target_el = select_random_el(RCU_Q_LEN);
+ j = 0;
+ QLIST_FOREACH_RCU(el, &Q_list_head, entry) {
+ j++;
+ if (target_el == j) {
+ prev_el = g_new(struct list_element, 1);
+ atomic_add(&n_nodes, 1);
+ prev_el->val = atomic_read(&n_nodes);
+ QLIST_INSERT_BEFORE_RCU(el, prev_el, entry);
+ break;
+ }
+ }
+ }
+ n_updates_local += 2;
+ synchronize_rcu();
+ }
+ rcu_quiescent_state();
+ atomic_add(&n_updates, n_updates_local);
+ atomic_add(&n_nodes_removed, n_removed_local);
+ return NULL;
+}
+
+static void rcu_qtest_init(void)
+{
+ struct list_element *new_el;
+ int i;
+ nthreadsrunning = 0;
+ srand(time(0));
+ for (i = 0; i < RCU_Q_LEN; i++) {
+ new_el = g_new(struct list_element, 1);
+ new_el->val = i;
+ QLIST_INSERT_HEAD_RCU(&Q_list_head, new_el, entry);
+ }
+ atomic_add(&n_nodes, RCU_Q_LEN);
+}
+
+static void rcu_qtest_run(int duration, int nreaders)
+{
+ int nthreads = nreaders + 1;
+ while (atomic_read(&nthreadsrunning) < nthreads) {
+ g_usleep(1000);
+ }
+
+ goflag = GOFLAG_RUN;
+ sleep(duration);
+ goflag = GOFLAG_STOP;
+ wait_all_threads();
+}
+
+
+static void rcu_qtest(const char *test, int duration, int nreaders)
+{
+ int i;
+ long long n_removed_local=0;
+
+ struct list_element *el, *prev_el;
+
+ rcu_qtest_init();
+ for (i = 0; i < nreaders; i++) {
+ create_thread(rcu_q_reader);
+ }
+ create_thread(rcu_q_updater);
+ rcu_qtest_run(duration, nreaders);
+ rcu_thread_offline();
+
+ QLIST_FOREACH_SAFE_RCU(prev_el, &Q_list_head, entry, el) {
+ QLIST_REMOVE_RCU(prev_el, entry);
+ call_rcu1(&prev_el->rcu, reclaim_list_el);
+ n_removed_local++;
+ }
+ atomic_add(&n_nodes_removed, n_removed_local);
+ rcu_quiescent_state();
+ synchronize_rcu();
+ while (n_nodes_removed > n_reclaims){
+ rcu_quiescent_state();
+ g_usleep(100);
+ synchronize_rcu();
+ }
+ printf("%s: %d readers; 1 updater; nodes read: %lld, nodes removed: %lld;
nodes reclaimed: %lld\n",
+ test, nthreadsrunning -1, n_reads, n_nodes_removed, n_reclaims);
+ exit(0);
+}
+
+static void usage(int argc, char *argv[])
+{
+ fprintf(stderr, "Usage: %s duration nreaders\n", argv[0]);
+ exit(-1);
+}
+
+
+int main(int argc, char *argv[])
+{
+ int duration = 0, readers = 0;
+
+ if (argc >= 2) {
+ duration = strtoul(argv[1], NULL, 0);
+ }
+ if (argc >= 3) {
+ readers = strtoul(argv[2], NULL, 0);
+ }
+
+ /* This thread is not part of the test. */
+ rcu_thread_offline();
+ if (duration && readers)
+ rcu_qtest(argv[0], duration, readers);
+ usage(argc, argv);
+ return 0;
+}
--
1.8.3.1
- [Qemu-devel] [RFC PATCH] Introduce RCU-enabled DQs (v2),
Mike Day <=