Re: [Qemu-devel] [PATCH 4/9] rcu: introduce RCU-enabled QLIST

[Fam Zheng]

On Tue, 02/03 13:52, Paolo Bonzini wrote:
> From: Mike Day <address@hidden>
> 
> 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 <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  hw/9pfs/virtio-9p-synth.c |   2 +-
>  include/qemu/queue.h      |  11 --
>  include/qemu/rcu_queue.h  | 134 ++++++++++++++++++++
>  tests/Makefile            |   5 +-
>  tests/test-rcu-list.c     | 306 
> ++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 445 insertions(+), 13 deletions(-)
>  create mode 100644 include/qemu/rcu_queue.h
>  create mode 100644 tests/test-rcu-list.c
> 
> diff --git a/hw/9pfs/virtio-9p-synth.c b/hw/9pfs/virtio-9p-synth.c
> index e75aa87..a0ab9a8 100644
> --- a/hw/9pfs/virtio-9p-synth.c
> +++ b/hw/9pfs/virtio-9p-synth.c
> @@ -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 */
> diff --git a/include/qemu/queue.h b/include/qemu/queue.h
> index c602797..8094150 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..3aca7a5
> --- /dev/null
> +++ b/include/qemu/rcu_queue.h
> @@ -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 */
> diff --git a/tests/Makefile b/tests/Makefile
> index db5b3c3..ef8d589 100644
> --- a/tests/Makefile
> +++ b/tests/Makefile
> @@ -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$(EXESUF): tests/rcutorture.o libqemuutil.a
> +tests/test-rcu-list$(EXESUF): tests/test-rcu-list.o libqemuutil.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\
> diff --git a/tests/test-rcu-list.c b/tests/test-rcu-list.c
> new file mode 100644
> index 0000000..5ce55e9
> --- /dev/null
> +++ b/tests/test-rcu-list.c
> @@ -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.
> + */
> +
> +/*
> + * Test variables.
> + */

Move below the includes?

> +
> +#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"
> +
> +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();

Is one of two synchronize_rcu's superfluous? Otherwise looks good:

Reviewed-by: Fam Zheng <address@hidden>

> +    atomic_add(&n_updates, n_updates_local);
> +    atomic_add(&n_nodes_removed, n_removed_local);
> +    return NULL;
> +}

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