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rcu: introduce RCU-enabled QLIST 

Add RCU-enabled variants on the existing bsd DQ facility. Each
operation has the same interface as the existing (non-RCU)
version. Also, each operation is implemented as macro.

Using the RCU-enabled QLIST, existing QLIST users will be able to
convert to RCU without using a different list interface.

Signed-off-by: Mike Day <ncmike@ncultra.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Mike Day 2013-08-27 11:38:45 -04:00 committed by Paolo Bonzini
parent 79e2b9aecc
commit 341774fe6c
5 changed files with 445 additions and 13 deletions
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2
hw/9pfs/virtio-9p-synth.c
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@ -18,7 +18,7 @@
#include "fsdev/qemu-fsdev.h"
#include "virtio-9p-synth.h"
#include "qemu/rcu.h"
#include "qemu/rcu_queue.h"
#include <sys/stat.h>
/* Root node for synth file system */

11
include/qemu/queue.h
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@ -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 = \

134
include/qemu/rcu_queue.h Normal file
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@ -0,0 +1,134 @@
#ifndef QEMU_RCU_QUEUE_H
#define QEMU_RCU_QUEUE_H
/*
* rcu_queue.h
*
* RCU-friendly versions of the queue.h primitives.
*
* 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/queue.h"
#include "qemu/atomic.h"
#ifdef __cplusplus
extern "C" {
#endif
/*
* List access methods.
*/
#define QLIST_EMPTY_RCU(head) (atomic_rcu_read(&(head)->lh_first) == NULL)
#define QLIST_FIRST_RCU(head) (atomic_rcu_read(&(head)->lh_first))
#define QLIST_NEXT_RCU(elm, field) (atomic_rcu_read(&(elm)->field.le_next))
/*
* 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; \
} \
*(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) = atomic_rcu_read(&(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) = atomic_rcu_read(&(var)->field.le_next), 1); \
(var) = (next_var))
#ifdef __cplusplus
}
#endif
#endif /* QEMU_RCU_QUEUE.H */

5
tests/Makefile
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@ -62,6 +62,8 @@ check-unit-y += tests/test-int128$(EXESUF)
gcov-files-test-int128-y =
check-unit-y += tests/rcutorture$(EXESUF)
gcov-files-rcutorture-y = util/rcu.c
check-unit-y += tests/test-rcu-list$(EXESUF)
gcov-files-test-rcu-list-y = util/rcu.c
check-unit-y += tests/test-bitops$(EXESUF)
check-unit-$(CONFIG_HAS_GLIB_SUBPROCESS_TESTS) += tests/test-qdev-global-props$(EXESUF)
check-unit-y += tests/check-qom-interface$(EXESUF)
@ -226,7 +228,7 @@ test-obj-y = tests/check-qint.o tests/check-qstring.o tests/check-qdict.o \
tests/test-qmp-commands.o tests/test-visitor-serialization.o \
tests/test-x86-cpuid.o tests/test-mul64.o tests/test-int128.o \
tests/test-opts-visitor.o tests/test-qmp-event.o \
tests/rcutorture.o
tests/rcutorture.o tests/test-rcu-list.o
test-qapi-obj-y = tests/test-qapi-visit.o tests/test-qapi-types.o \
tests/test-qapi-event.o
@ -256,6 +258,7 @@ tests/test-xbzrle$(EXESUF): tests/test-xbzrle.o migration/xbzrle.o page_cache.o
tests/test-cutils$(EXESUF): tests/test-cutils.o util/cutils.o
tests/test-int128$(EXESUF): tests/test-int128.o
tests/rcutorture$(EXESUF): tests/rcutorture.o libqemuutil.a libqemustub.a
tests/test-rcu-list$(EXESUF): tests/test-rcu-list.o libqemuutil.a libqemustub.a
tests/test-qdev-global-props$(EXESUF): tests/test-qdev-global-props.o \
hw/core/qdev.o hw/core/qdev-properties.o hw/core/hotplug.o\

306
tests/test-rcu-list.c Normal file
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@ -0,0 +1,306 @@
/*
* 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.
*/
#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/osdep.h"
#include "qemu/thread.h"
#include "qemu/rcu_queue.h"
/*
* Test variables.
*/
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 g_test_in_charge = 0;
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], "test", 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;
*(struct rcu_reader_data **)arg = &rcu_reader;
atomic_inc(&nthreadsrunning);
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
rcu_read_lock();
QLIST_FOREACH_RCU(el, &Q_list_head, entry) {
j = atomic_read(&el->val);
(void)j;
n_reads_local++;
if (goflag == GOFLAG_STOP) {
break;
}
}
rcu_read_unlock();
g_usleep(100);
}
atomic_add(&n_reads, n_reads_local);
return NULL;
}
static void *rcu_q_updater(void *arg)
{
int 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 = &rcu_reader;
atomic_inc(&nthreadsrunning);
while (goflag == GOFLAG_INIT) {
g_usleep(1000);
}
while (goflag == GOFLAG_RUN) {
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();
}
synchronize_rcu();
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);
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);
synchronize_rcu();
while (n_nodes_removed > n_reclaims) {
g_usleep(100);
synchronize_rcu();
}
if (g_test_in_charge) {
g_assert_cmpint(n_nodes_removed, ==, n_reclaims);
} else {
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);
}
static int gtest_seconds;
static void gtest_rcuq_one(void)
{
rcu_qtest("rcuqtest", gtest_seconds / 4, 1);
}
static void gtest_rcuq_few(void)
{
rcu_qtest("rcuqtest", gtest_seconds / 4, 5);
}
static void gtest_rcuq_many(void)
{
rcu_qtest("rcuqtest", gtest_seconds / 2, 20);
}
int main(int argc, char *argv[])
{
int duration = 0, readers = 0;
if (argc >= 2) {
if (argv[1][0] == '-') {
g_test_init(&argc, &argv, NULL);
if (g_test_quick()) {
gtest_seconds = 4;
} else {
gtest_seconds = 20;
}
g_test_add_func("/rcu/qlist/single-threaded", gtest_rcuq_one);
g_test_add_func("/rcu/qlist/short-few", gtest_rcuq_few);
g_test_add_func("/rcu/qlist/long-many", gtest_rcuq_many);
g_test_in_charge = 1;
return g_test_run();
}
duration = strtoul(argv[1], NULL, 0);
}
if (argc >= 3) {
readers = strtoul(argv[2], NULL, 0);
}
if (duration && readers) {
rcu_qtest(argv[0], duration, readers);
return 0;
}
usage(argc, argv);
return -1;
}