[lttng-dev] [URCU PATCH 3/3] call_rcu: use wfcqueue, eliminate false-sharing
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Tue Oct 2 10:16:38 EDT 2012
Eliminate false-sharing between call_rcu (enqueuer) and worker threads
on the queue head and tail.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 81718bb..c92bbe6 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -30,14 +30,14 @@ if COMPAT_FUTEX
COMPAT+=$(top_srcdir)/compat_futex.c
endif
-URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
-URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
+URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
+URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
# URCU_MB uses urcu.c but -DRCU_MB must be defined
-URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
+URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
# URCU_SIGNAL uses urcu.c but -DRCU_SIGNAL must be defined
-URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
-URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
-URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT)
+URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
+URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
+URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfcqueue.c $(COMPAT)
URCU_COMMON_LIB=$(top_builddir)/liburcu-common.la
URCU_LIB=$(top_builddir)/liburcu.la
diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
index 13b24ff..cf65992 100644
--- a/urcu-call-rcu-impl.h
+++ b/urcu-call-rcu-impl.h
@@ -21,6 +21,7 @@
*/
#define _GNU_SOURCE
+#define _LGPL_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
@@ -35,7 +36,7 @@
#include <sched.h>
#include "config.h"
-#include "urcu/wfqueue.h"
+#include "urcu/wfcqueue.h"
#include "urcu-call-rcu.h"
#include "urcu-pointer.h"
#include "urcu/list.h"
@@ -46,7 +47,14 @@
/* Data structure that identifies a call_rcu thread. */
struct call_rcu_data {
- struct cds_wfq_queue cbs;
+ /*
+ * Align the tail on cache line size to eliminate false-sharing
+ * with head.
+ */
+ struct cds_wfcq_tail __attribute__((aligned(CAA_CACHE_LINE_SIZE))) cbs_tail;
+ /* Alignment on cache line size will add padding here */
+
+ struct cds_wfcq_head cbs_head;
unsigned long flags;
int32_t futex;
unsigned long qlen; /* maintained for debugging. */
@@ -220,10 +228,7 @@ static void call_rcu_wake_up(struct call_rcu_data *crdp)
static void *call_rcu_thread(void *arg)
{
unsigned long cbcount;
- struct cds_wfq_node *cbs;
- struct cds_wfq_node **cbs_tail;
- struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
- struct rcu_head *rhp;
+ struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
int ret;
@@ -243,35 +248,33 @@ static void *call_rcu_thread(void *arg)
cmm_smp_mb();
}
for (;;) {
- if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
- while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
- poll(NULL, 0, 1);
- _CMM_STORE_SHARED(crdp->cbs.head, NULL);
- cbs_tail = (struct cds_wfq_node **)
- uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
+ struct cds_wfcq_head cbs_tmp_head;
+ struct cds_wfcq_tail cbs_tmp_tail;
+ struct cds_wfcq_node *cbs, *cbs_tmp_n;
+
+ cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
+ __cds_wfcq_splice_blocking(&cbs_tmp_head, &cbs_tmp_tail,
+ &crdp->cbs_head, &crdp->cbs_tail);
+ if (!cds_wfcq_empty(&cbs_tmp_head, &cbs_tmp_tail)) {
synchronize_rcu();
cbcount = 0;
- do {
- while (cbs->next == NULL &&
- &cbs->next != cbs_tail)
- poll(NULL, 0, 1);
- if (cbs == &crdp->cbs.dummy) {
- cbs = cbs->next;
- continue;
- }
- rhp = (struct rcu_head *)cbs;
- cbs = cbs->next;
+ __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++;
- } while (cbs != NULL);
+ }
uatomic_sub(&crdp->qlen, cbcount);
}
if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
break;
rcu_thread_offline();
if (!rt) {
- if (&crdp->cbs.head
- == _CMM_LOAD_SHARED(crdp->cbs.tail)) {
+ if (cds_wfcq_empty(&crdp->cbs_head,
+ &crdp->cbs_tail)) {
call_rcu_wait(crdp);
poll(NULL, 0, 10);
uatomic_dec(&crdp->futex);
@@ -317,7 +320,7 @@ static void call_rcu_data_init(struct call_rcu_data **crdpp,
if (crdp == NULL)
urcu_die(errno);
memset(crdp, '\0', sizeof(*crdp));
- cds_wfq_init(&crdp->cbs);
+ cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
crdp->qlen = 0;
crdp->futex = 0;
crdp->flags = flags;
@@ -590,12 +593,12 @@ void call_rcu(struct rcu_head *head,
{
struct call_rcu_data *crdp;
- cds_wfq_node_init(&head->next);
+ cds_wfcq_node_init(&head->next);
head->func = func;
/* Holding rcu read-side lock across use of per-cpu crdp */
rcu_read_lock();
crdp = get_call_rcu_data();
- cds_wfq_enqueue(&crdp->cbs, &head->next);
+ cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
uatomic_inc(&crdp->qlen);
wake_call_rcu_thread(crdp);
rcu_read_unlock();
@@ -625,10 +628,6 @@ void call_rcu(struct rcu_head *head,
*/
void call_rcu_data_free(struct call_rcu_data *crdp)
{
- struct cds_wfq_node *cbs;
- struct cds_wfq_node **cbs_tail;
- struct cds_wfq_node **cbs_endprev;
-
if (crdp == NULL || crdp == default_call_rcu_data) {
return;
}
@@ -638,17 +637,12 @@ void call_rcu_data_free(struct call_rcu_data *crdp)
while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
poll(NULL, 0, 1);
}
- if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
- while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
- poll(NULL, 0, 1);
- _CMM_STORE_SHARED(crdp->cbs.head, NULL);
- cbs_tail = (struct cds_wfq_node **)
- uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
+ if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
/* Create default call rcu data if need be */
(void) get_default_call_rcu_data();
- cbs_endprev = (struct cds_wfq_node **)
- uatomic_xchg(&default_call_rcu_data, cbs_tail);
- *cbs_endprev = cbs;
+ __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
+ &default_call_rcu_data->cbs_tail,
+ &crdp->cbs_head, &crdp->cbs_tail);
uatomic_add(&default_call_rcu_data->qlen,
uatomic_read(&crdp->qlen));
wake_call_rcu_thread(default_call_rcu_data);
diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
index f7eac8d..1dad0e2 100644
--- a/urcu-call-rcu.h
+++ b/urcu-call-rcu.h
@@ -32,7 +32,7 @@
#include <stdlib.h>
#include <pthread.h>
-#include <urcu/wfqueue.h>
+#include <urcu/wfcqueue.h>
#ifdef __cplusplus
extern "C" {
@@ -55,7 +55,7 @@ struct call_rcu_data;
*/
struct rcu_head {
- struct cds_wfq_node next;
+ struct cds_wfcq_node next;
void (*func)(struct rcu_head *head);
};
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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