[ltt-dev] [rp] [PATCH RFC] v2 call_rcu() interface for userspace-rcu
Paul E. McKenney
paulmck at linux.vnet.ibm.com
Sat Feb 12 01:12:57 EST 2011
On Fri, Feb 11, 2011 at 08:46:44PM -0500, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> > Adds call_rcu(), with RCU threads to invoke the callbacks. By default,
> > there will be one such RCU thread per process, created the first time
> > that call_rcu() is invoked. On systems supporting sched_getcpu(), it
> > is possible to create one RCU thread per CPU by calling
> > create_all_cpu_call_rcu_data().
> >
> > This version includes feedback from Mathieu Desnoyers and forward-ports
> > to the new cds naming scheme. Note that v1 was posted on October 29th.
>
> Hi Paul,
>
> The interfaces have improved a lot, thanks ! Here are a few comments,
>
> >
> > Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> >
> > diff --git a/Makefile.am b/Makefile.am
> > index 79a7152..64bb299 100644
> > --- a/Makefile.am
> > +++ b/Makefile.am
> > @@ -29,8 +29,8 @@ COMPAT+=compat_futex.c
> > endif
> >
> > lib_LTLIBRARIES = liburcu.la liburcu-qsbr.la liburcu-mb.la liburcu-signal.la \
> > - liburcu-bp.la liburcu-defer.la libwfqueue.la libwfstack.la \
> > - librculfqueue.la librculfstack.la
> > + liburcu-bp.la liburcu-defer.la liburcu-call.la \
> > + libwfqueue.la libwfstack.la librculfqueue.la librculfstack.la
> >
> > liburcu_la_SOURCES = urcu.c urcu-pointer.c $(COMPAT)
> >
> > @@ -44,6 +44,7 @@ liburcu_signal_la_CFLAGS = -DRCU_SIGNAL
> >
> > liburcu_bp_la_SOURCES = urcu-bp.c urcu-pointer.c $(COMPAT)
> >
> > +liburcu_call_la_SOURCES = urcu-call-rcu.c $(COMPAT)
> > liburcu_defer_la_SOURCES = urcu-defer.c $(COMPAT)
> >
> > libwfqueue_la_SOURCES = wfqueue.c $(COMPAT)
> > diff --git a/configure.ac b/configure.ac
> > index 02780e7..88771d4 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -34,7 +34,7 @@ AC_TYPE_SIZE_T
> > # Checks for library functions.
> > AC_FUNC_MALLOC
> > AC_FUNC_MMAP
> > -AC_CHECK_FUNCS([bzero gettimeofday munmap strtoul])
> > +AC_CHECK_FUNCS([bzero gettimeofday munmap sched_getcpu strtoul sysconf])
> > # Find arch type
> > case $host_cpu in
> > diff --git a/tests/Makefile.am b/tests/Makefile.am
> > index a43dd75..3c025a4 100644
> > --- a/tests/Makefile.am
> > +++ b/tests/Makefile.am
> > @@ -1,5 +1,5 @@
> > AM_LDFLAGS=-lpthread
> > -AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir)
> > +AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir) -g
>
> It makes me think: I noticed this week that -Wall is missing from the top level
> build options. We should really add it.
Fair enough. It did find a nasty uninitialized variable, so worth it in
this case. The ignored return values from write() I leave to you. ;-)
Ditto the "warning: value computed is not used" in rculfqueue-static.h.
> > noinst_PROGRAMS = test_urcu test_urcu_dynamic_link test_urcu_timing \
> > test_urcu_signal test_urcu_signal_dynamic_link test_urcu_signal_timing \
> > @@ -28,20 +28,21 @@ if COMPAT_FUTEX
> > COMPAT+=$(top_srcdir)/compat_futex.c
> > endif
> >
> > -URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > -URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > +URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > +URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > # URCU_MB uses urcu.c but -DRCU_MB must be defined
> > -URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > +URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > # URCU_SIGNAL uses urcu.c but -DRCU_SIGNAL must be defined
> > -URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > -URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > -URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-defer.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > +URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > +URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > +URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-defer.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> >
> > URCU_LIB=$(top_builddir)/liburcu.la
> > URCU_QSBR_LIB=$(top_builddir)/liburcu-qsbr.la
> > URCU_MB_LIB=$(top_builddir)/liburcu-mb.la
> > URCU_SIGNAL_LIB=$(top_builddir)/liburcu-signal.la
> > URCU_BP_LIB=$(top_builddir)/liburcu-bp.la
> > +URCU_CALL_LIB=$(top_builddir)/liburcu-call.la
> > WFQUEUE_LIB=$(top_builddir)/libwfqueue.la
> > WFSTACK_LIB=$(top_builddir)/libwfstack.la
> > RCULFQUEUE_LIB=$(top_builddir)/librculfqueue.la
> > @@ -95,23 +96,23 @@ test_perthreadlock_SOURCES = test_perthreadlock.c $(URCU_SIGNAL)
> >
> > rcutorture_urcu_SOURCES = urcutorture.c
> > rcutorture_urcu_CFLAGS = -DTORTURE_URCU $(AM_CFLAGS)
> > -rcutorture_urcu_LDADD = $(URCU)
> > +rcutorture_urcu_LDADD = $(URCU) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> >
> > rcutorture_urcu_mb_SOURCES = urcutorture.c
> > rcutorture_urcu_mb_CFLAGS = -DTORTURE_URCU_MB $(AM_CFLAGS)
> > -rcutorture_urcu_mb_LDADD = $(URCU_MB_LIB)
> > +rcutorture_urcu_mb_LDADD = $(URCU_MB_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> >
> > rcutorture_qsbr_SOURCES = urcutorture.c
> > rcutorture_qsbr_CFLAGS = -DTORTURE_QSBR $(AM_CFLAGS)
> > -rcutorture_qsbr_LDADD = $(URCU_QSBR_LIB)
> > +rcutorture_qsbr_LDADD = $(URCU_QSBR_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> >
> > rcutorture_urcu_signal_SOURCES = urcutorture.c
> > rcutorture_urcu_signal_CFLAGS = -DTORTURE_URCU_SIGNAL $(AM_CFLAGS)
> > -rcutorture_urcu_signal_LDADD = $(URCU_SIGNAL_LIB)
> > +rcutorture_urcu_signal_LDADD = $(URCU_SIGNAL_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> >
> > rcutorture_urcu_bp_SOURCES = urcutorture.c
> > rcutorture_urcu_bp_CFLAGS = -DTORTURE_URCU_BP $(AM_CFLAGS)
> > -rcutorture_urcu_bp_LDADD = $(URCU_BP_LIB)
> > +rcutorture_urcu_bp_LDADD = $(URCU_BP_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> >
> > test_mutex_SOURCES = test_mutex.c $(URCU)
> >
> > diff --git a/tests/rcutorture.h b/tests/rcutorture.h
> > index 4dac2f2..207d9f8 100644
> > --- a/tests/rcutorture.h
> > +++ b/tests/rcutorture.h
> > @@ -65,6 +65,8 @@
> > * Test variables.
> > */
> >
> > +#include "../urcu-call-rcu.h"
> > +
> > DEFINE_PER_THREAD(long long, n_reads_pt);
> > DEFINE_PER_THREAD(long long, n_updates_pt);
> >
> > @@ -296,10 +298,30 @@ void *rcu_read_stress_test(void *arg)
> > return (NULL);
> > }
> >
> > +static pthread_mutex_t call_rcu_test_mutex = PTHREAD_MUTEX_INITIALIZER;
> > +static pthread_cond_t call_rcu_test_cond = PTHREAD_COND_INITIALIZER;
> > +
> > +void rcu_update_stress_test_rcu(struct rcu_head *head)
> > +{
> > + if (pthread_mutex_lock(&call_rcu_test_mutex) != 0) {
> > + perror("pthread_mutex_lock");
> > + exit(-1);
> > + }
> > + if (pthread_cond_signal(&call_rcu_test_cond) != 0) {
> > + perror("pthread_cond_signal");
> > + exit(-1);
> > + }
> > + if (pthread_mutex_unlock(&call_rcu_test_mutex) != 0) {
> > + perror("pthread_mutex_unlock");
> > + exit(-1);
> > + }
> > +}
> > +
> > void *rcu_update_stress_test(void *arg)
> > {
> > int i;
> > struct rcu_stress *p;
> > + struct rcu_head rh;
> >
> > while (goflag == GOFLAG_INIT)
> > poll(NULL, 0, 1);
> > @@ -317,7 +339,24 @@ void *rcu_update_stress_test(void *arg)
> > for (i = 0; i < RCU_STRESS_PIPE_LEN; i++)
> > if (i != rcu_stress_idx)
> > rcu_stress_array[i].pipe_count++;
> > - synchronize_rcu();
> > + if (n_updates & 0x1)
> > + synchronize_rcu();
> > + else {
> > + if (pthread_mutex_lock(&call_rcu_test_mutex) != 0) {
> > + perror("pthread_mutex_lock");
> > + exit(-1);
> > + }
> > + call_rcu(&rh, rcu_update_stress_test_rcu);
> > + if (pthread_cond_wait(&call_rcu_test_cond,
> > + &call_rcu_test_mutex) != 0) {
> > + perror("pthread_cond_wait");
> > + exit(-1);
> > + }
> > + if (pthread_mutex_unlock(&call_rcu_test_mutex) != 0) {
> > + perror("pthread_mutex_unlock");
> > + exit(-1);
> > + }
> > + }
> > n_updates++;
> > }
> > return NULL;
> > diff --git a/urcu-call-rcu.c b/urcu-call-rcu.c
> > new file mode 100644
> > index 0000000..d59a2d7
> > --- /dev/null
> > +++ b/urcu-call-rcu.c
> > @@ -0,0 +1,405 @@
> > +/*
> > + * urcu-call-rcu.c
> > + *
> > + * Userspace RCU library - batch memory reclamation with kernel API
> > + *
> > + * Copyright (c) 2010 Paul E. McKenney <paulmck at linux.vnet.ibm.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
> > + */
> > +
> > +#include <stdio.h>
> > +#include <pthread.h>
> > +#include <signal.h>
> > +#include <assert.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <errno.h>
> > +#include <poll.h>
> > +#include <sys/time.h>
> > +#include <syscall.h>
> > +#include <unistd.h>
> > +
> > +#include "config.h"
> > +#include "urcu/wfqueue.h"
> > +#include "urcu-call-rcu.h"
> > +#include "urcu-pointer.h"
> > +
> > +/* Data structure that identifies a call_rcu thread. */
> > +
> > +struct call_rcu_data {
> > + struct cds_wfq_queue cbs;
> > + unsigned long flags;
> > + pthread_mutex_t mtx;
> > + pthread_cond_t cond;
> > + unsigned long qlen;
> > + pthread_t tid;
> > +} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
> > +
> > +/* Link a thread using call_rcu() to its call_rcu thread. */
> > +
> > +static __thread struct call_rcu_data *thread_call_rcu_data;
> > +
> > +/* Guard call_rcu thread creation. */
> > +
> > +static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
> > +
> > +/* If a given thread does not have its own call_rcu thread, this is default. */
> > +
> > +static struct call_rcu_data *default_call_rcu_data;
> > +
> > +extern void synchronize_rcu(void);
> > +
> > +/*
> > + * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
> > + * available, then we can have call_rcu threads assigned to individual
> > + * CPUs rather than only to specific threads.
> > + */
> > +
> > +#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
> > +
> > +/*
> > + * Pointer to array of pointers to per-CPU call_rcu_data structures
> > + * and # CPUs.
> > + */
> > +
> > +static struct call_rcu_data **per_cpu_call_rcu_data;
> > +static long maxcpus;
> > +
> > +/* Allocate the array if it has not already been allocated. */
> > +
> > +static void alloc_cpu_call_rcu_data(void)
> > +{
> > + struct call_rcu_data **p;
> > +
> > + if (maxcpus != 0)
> > + return;
> > + maxcpus = sysconf(_SC_NPROCESSORS_CONF);
>
> I noticed an odd sysconf behavior inside a chroot jail where /proc was not
> mounted: it returns 1 single CPU for _SC_NPROCESSORS_CONF, which would be
> catastrophic here because the array would be too small to match the index
> returned by sched_getcpu. Any thought on how we should deal with this ?
> Maybe doing an extra value sanity check in our own wrapper over sched_getcpu
> would be appropriate ?
Good catch, we do need a range check in get_call_rcu_data(), which I
I have added. That is the only sched_getcpu() in the call_rcu() code,
so that should cover it. If the CPU is out of range, we fall back to
the default global CPU.
> > + if (maxcpus == -1)
> > + return;
> > + p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
>
> Shouldn't we yell or something if p is null ? :-)
If p is NULL, it will just force use of the global call_rcu() thread.
The data for this thread is static, so always there.
But what form of yelling did you have in mind?
> > + if (p != NULL)
> > + memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
> > +}
> > +
> > +#else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> > +
> > +static const struct call_rcu_data **per_cpu_call_rcu_data = NULL;
> > +static const long maxcpus = -1;
> > +
> > +static void alloc_cpu_call_rcu_data(void)
> > +{
> > +}
> > +
> > +static int sched_getcpu(void)
> > +{
> > + return -1;
> > +}
> > +
> > +#endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> > +
> > +/* Acquire the specified pthread mutex. */
> > +
> > +static void call_rcu_lock(pthread_mutex_t *pmp)
> > +{
> > + if (pthread_mutex_lock(pmp) != 0) {
> > + perror("pthread_mutex_lock");
> > + exit(-1);
> > + }
> > +}
> > +
> > +/* Release the specified pthread mutex. */
> > +
> > +static void call_rcu_unlock(pthread_mutex_t *pmp)
> > +{
> > + if (pthread_mutex_unlock(pmp) != 0) {
> > + perror("pthread_mutex_unlock");
> > + exit(-1);
> > + }
> > +}
> > +
> > +/* This is the code run by each call_rcu thread. */
> > +
> > +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;
> > +
> > + thread_call_rcu_data = crdp;
> > + 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);
> > + 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;
> > + rhp->func(rhp);
> > + cbcount++;
> > + } while (cbs != NULL);
> > + uatomic_sub(&crdp->qlen, cbcount);
> > + }
> > + if (crdp->flags & URCU_CALL_RCU_RT)
> > + poll(NULL, 0, 10);
> > + else {
> > + call_rcu_lock(&crdp->mtx);
> > + _CMM_STORE_SHARED(crdp->flags,
> > + crdp->flags & ~URCU_CALL_RCU_RUNNING);
> > + if (&cbs->next != crdp->cbs.tail &&
> > + pthread_cond_wait(&crdp->cond, &crdp->mtx) != 0) {
> > + perror("pthread_cond_wait");
> > + exit(-1);
> > + }
> > + _CMM_STORE_SHARED(crdp->flags,
> > + crdp->flags | URCU_CALL_RCU_RUNNING);
> > + poll(NULL, 0, 10);
> > + call_rcu_unlock(&crdp->mtx);
> > + }
> > + }
> > + return NULL; /* NOTREACHED */
>
> I'm not sure how this thread is supposed to clean up properly at process exit ?
Given that all it has is in-memory data structures, when exit() makes
the address space vanish, that will implicity clean things up for this
thread.
Or am I missing your point?
> > +}
> > +
> > +/*
> > + * Create both a call_rcu thread and the corresponding call_rcu_data
> > + * structure, linking the structure in as specified.
> > + */
> > +
> > +void call_rcu_data_init(struct call_rcu_data **crdpp, unsigned long flags)
> > +{
> > + struct call_rcu_data *crdp;
> > +
> > + crdp = malloc(sizeof(*crdp));
> > + if (crdp == NULL) {
> > + fprintf(stderr, "Out of memory.\n");
> > + exit(-1);
> > + }
> > + memset(crdp, '\0', sizeof(*crdp));
> > + cds_wfq_init(&crdp->cbs);
> > + crdp->qlen = 0;
> > + if (pthread_mutex_init(&crdp->mtx, NULL) != 0) {
> > + perror("pthread_mutex_init");
> > + exit(-1);
> > + }
> > + if (pthread_cond_init(&crdp->cond, NULL) != 0) {
> > + perror("pthread_cond_init");
> > + exit(-1);
> > + }
> > + crdp->flags = flags | URCU_CALL_RCU_RUNNING;
> > + cmm_smp_mb(); /* Structure initialized before pointer is planted. */
> > + *crdpp = crdp;
> > + if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
> > + perror("pthread_create");
> > + exit(-1);
> > + }
> > +}
> > +
> > +/*
> > + * Return a pointer to the call_rcu_data structure for the specified
> > + * CPU, returning NULL if there is none. We cannot automnatically
>
> automnatically -> automatically
Good eyes, fixed.
But wouldn't you really prefer automaniacally? ;-)
> > + * created it because the platform we are running on might not define
> > + * sched_getcpu().
> > + */
> > +
> > +struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
> > +{
> > + if (per_cpu_call_rcu_data == NULL)
> > + return NULL;
> > + if (cpu < 0 || maxcpus <= cpu)
> > + return NULL;
>
> Ah! I think this is where is would make sense to validate that "cpu" is not out
> of bounds. If it is, then we could fallback on the default call_rcu thread, or
> yell about lack of /proc.
You lost me here -- we are validating that the "cpu" is not out of bounds
with respect to the array bounds. The caller sees the NULL pointer and
acts accordingly.
I did need to add a check to get_call_rcu_data() down below, which I did.
> > + return per_cpu_call_rcu_data[cpu];
> > +}
> > +
> > +/*
> > + * Return the tid corresponding to the call_rcu thread whose
> > + * call_rcu_data structure is specified.
> > + */
> > +
> > +pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
> > +{
> > + return crdp->tid;
> > +}
> > +
> > +/*
> > + * Create a call_rcu_data structure (with thread) and return a pointer.
> > + */
> > +
> > +struct call_rcu_data *create_call_rcu_data(unsigned long flags)
> > +{
> > + struct call_rcu_data *crdp;
> > +
> > + call_rcu_data_init(&crdp, flags);
> > + return crdp;
> > +}
> > +
> > +/*
> > + * Set the specified CPU to use the specified call_rcu_data structure.
> > + */
> > +
> > +int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
> > +{
> > + call_rcu_lock(&call_rcu_mutex);
> > + alloc_cpu_call_rcu_data();
> > + call_rcu_unlock(&call_rcu_mutex);
> > + if (cpu < 0 || maxcpus <= cpu || per_cpu_call_rcu_data == NULL)
> > + return 0;
> > + per_cpu_call_rcu_data[cpu] = crdp;
>
> another point where we chould validate that cpu is not out of bound.
The validation is already there: "cpu < 0 || maxcpus <= cpu".
What am I missing here?
> > + return 1;
> > +}
> > +
> > +/*
> > + * Return a pointer to the default call_rcu_data structure, creating
> > + * one if need be. Because we never free call_rcu_data structures,
> > + * we don't need to be in an RCU read-side critical section.
> > + */
> > +
> > +struct call_rcu_data *get_default_call_rcu_data(void)
> > +{
> > + if (default_call_rcu_data != NULL)
> > + return rcu_dereference(default_call_rcu_data);
> > + call_rcu_lock(&call_rcu_mutex);
> > + if (default_call_rcu_data != NULL) {
> > + call_rcu_unlock(&call_rcu_mutex);
> > + return default_call_rcu_data;
> > + }
> > + call_rcu_data_init(&default_call_rcu_data, 0);
> > + call_rcu_unlock(&call_rcu_mutex);
> > + return default_call_rcu_data;
> > +}
> > +
> > +/*
> > + * Return the call_rcu_data structure that applies to the currently
> > + * running thread. Any call_rcu_data structure assigned specifically
> > + * to this thread has first priority, followed by any call_rcu_data
> > + * structure assigned to the CPU on which the thread is running,
> > + * followed by the default call_rcu_data structure. If there is not
> > + * yet a default call_rcu_data structure, one will be created.
> > + */
> > +struct call_rcu_data *get_call_rcu_data(void)
> > +{
> > + int curcpu;
> > +
> > + if (thread_call_rcu_data != NULL)
> > + return thread_call_rcu_data;
> > + curcpu = sched_getcpu();
Now -here- we need validation. The following "if" becomes:
if (curcpu >= 0 && maxcpus > curcpu &&
per_cpu_call_rcu_data != NULL &&
per_cpu_call_rcu_data[curcpu] != NULL)
return per_cpu_call_rcu_data[curcpu];
> > + if (per_cpu_call_rcu_data != NULL &&
> > + per_cpu_call_rcu_data[curcpu] != NULL)
>
> Another array bounds validation here ?
Yep, see above.
> > + return per_cpu_call_rcu_data[curcpu];
> > + return get_default_call_rcu_data();
> > +}
> > +
> > +/*
> > + * Return a pointer to this task's call_rcu_data if there is one.
> > + */
> > +
> > +struct call_rcu_data *get_thread_call_rcu_data(void)
> > +{
> > + return thread_call_rcu_data;
> > +}
> > +
> > +/*
> > + * Set this task's call_rcu_data structure as specified, regardless
> > + * of whether or not this task already had one. (This allows switching
> > + * to and from real-time call_rcu threads, for example.)
> > + */
> > +
> > +void set_thread_call_rcu_data(struct call_rcu_data *crdp)
> > +{
> > + thread_call_rcu_data = crdp;
> > +}
> > +
> > +/*
> > + * Create a separate call_rcu thread for each CPU. This does not
> > + * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
> > + * function if you want that behavior.
> > + */
> > +
> > +int create_all_cpu_call_rcu_data(unsigned long flags)
> > +{
> > + int i;
> > + struct call_rcu_data *crdp;
> > +
> > + call_rcu_lock(&call_rcu_mutex);
> > + alloc_cpu_call_rcu_data();
> > + call_rcu_unlock(&call_rcu_mutex);
> > + if (maxcpus == -1 || per_cpu_call_rcu_data == NULL)
> > + return 0;
> > + for (i = 0; i < maxcpus; i++) {
> > + call_rcu_lock(&call_rcu_mutex);
> > + if (get_cpu_call_rcu_data(i)) {
> > + call_rcu_unlock(&call_rcu_mutex);
> > + continue;
> > + }
> > + crdp = create_call_rcu_data(flags);
>
> Hrm, just so we're clear: on a 8-way system with a kernel supporting up to 32
> possible cpus, this would create 32 threads per application. Is it really what
> we want ?
Only if the application invokes create_all_cpu_call_rcu_data().
If an application uses call_rcu() only rarely, then it should avoid
calling create_all_cpu_call_rcu_data(), instead relying on the single
default call_rcu() thread.
> For the non-RT case, we might want to investigate using sysconf get "online"
> cpus, and fixup dynamically within call_rcu() if we discover that
>
> 1) per-cpu rcu_data should be available
> 2) some data within our per-cpu rcu_data tells us that it has not been allocated
>
> So we could allocate the per-cpu rcu_data array for the number of possible cpus
> on the system, but only allocate more expensive ressources (e.g. create threads)
> for the number of online cpus, and dynamically spawn threads if needed.
>
> We could leave the code as is for the RT case (allocate threads for each
> possible cpus). Thoughts ?
I am for keeping it simple to begin with. On most modern systems,
I bet that the extra few tens of threads is not going to be a big deal.
> > + if (crdp == NULL) {
> > + call_rcu_unlock(&call_rcu_mutex);
> > + return 0;
> > + }
> > + if (!set_cpu_call_rcu_data(i, crdp)) {
> > + call_rcu_unlock(&call_rcu_mutex);
> > + return 0; /* should not happen, but... */
> > + }
> > + call_rcu_unlock(&call_rcu_mutex);
> > + }
> > + return 1;
> > +}
> > +
> > +/*
> > + * Schedule a function to be invoked after a following grace period.
> > + * This is the only function that must be called -- the others are
> > + * only present to allow applications to tune their use of RCU for
> > + * maximum performance.
> > + *
> > + * Note that unless a call_rcu thread has not already been created,
> > + * the first invocation of call_rcu() will create one. So, if you
> > + * need the first invocation of call_rcu() to be fast, make sure
> > + * to create a call_rcu thread first. One way to accomplish this is
> > + * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
> > + */
> > +
> > +void call_rcu(struct rcu_head *head,
> > + void (*func)(struct rcu_head *head))
> > +{
> > + struct call_rcu_data *crdp;
> > +
> > + cds_wfq_node_init(&head->next);
> > + head->func = func;
> > + crdp = get_call_rcu_data();
> > + cds_wfq_enqueue(&crdp->cbs, &head->next);
> > + uatomic_inc(&crdp->qlen);
> > + if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT)) {
> > + call_rcu_lock(&crdp->mtx);
> > + if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RUNNING)) {
> > + if (pthread_cond_signal(&crdp->cond) != 0) {
> > + perror("pthread_cond_signal");
> > + exit(-1);
> > + }
> > + }
> > + call_rcu_unlock(&crdp->mtx);
> > + }
> > +}
> > diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
> > new file mode 100644
> > index 0000000..b390b7e
> > --- /dev/null
> > +++ b/urcu-call-rcu.h
> > @@ -0,0 +1,80 @@
> > +#ifndef _URCU_CALL_RCU_H
> > +#define _URCU_CALL_RCU_H
> > +
> > +/*
> > + * urcu-defer.h
>
> urcu-call-rcu.h
Good catch, fixed.
> > + *
> > + * Userspace RCU header - deferred execution
> > + *
> > + * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
> > + *
> > + * LGPL-compatible code should include this header with :
> > + *
> > + * #define _LGPL_SOURCE
> > + * #include <urcu-defer.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
> > + */
> > +
> > +#include <stdlib.h>
> > +#include <pthread.h>
> > +
> > +#include "urcu/wfqueue.h"
>
> should this header be between < > instead ?
No idea, I was just copying the other examples using double quotes.
I fixed this one to use angle brackets, and leave the others to you.
> > +
> > +#ifdef __cplusplus
> > +extern "C" {
> > +#endif
> > +
> > +/* Note that struct call_rcu_data is opaque to callers. */
> > +
> > +struct call_rcu_data;
> > +
> > +/* Flag values. */
> > +
> > +#define URCU_CALL_RCU_RT 0x1
> > +#define URCU_CALL_RCU_RUNNING 0x2
> > +
> > +/*
> > + * The rcu_head data structure is placed in the structure to be freed
> > + * via call_rcu().
> > + */
> > +
> > +struct rcu_head {
> > + struct cds_wfq_node next;
> > + void (*func)(struct rcu_head *head);
> > +};
> > +
> > +/*
> > + * Exported functions
> > + */
> > +void call_rcu_data_init(struct call_rcu_data **crdpp, unsigned long flags);
> > +struct call_rcu_data *get_cpu_call_rcu_data(int cpu);
> > +pthread_t get_call_rcu_thread(struct call_rcu_data *crdp);
> > +struct call_rcu_data *create_call_rcu_data(unsigned long flags);
> > +int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp);
> > +struct call_rcu_data *get_default_call_rcu_data(void);
> > +struct call_rcu_data *get_call_rcu_data(void);
> > +struct call_rcu_data *get_thread_call_rcu_data(void);
> > +void set_thread_call_rcu_data(struct call_rcu_data *crdp);
> > +int create_all_cpu_call_rcu_data(unsigned long flags);
> > +void call_rcu(struct rcu_head *head,
> > + void (*func)(struct rcu_head *head));
> > +
> > +#ifdef __cplusplus
> > +}
> > +#endif
> > +
> > +#endif /* _URCU_CALL_RCU_H */
> > diff --git a/urcu-defer.h b/urcu-defer.h
> > index e161616..a64c75c 100644
> > --- a/urcu-defer.h
> > +++ b/urcu-defer.h
> > @@ -53,14 +53,6 @@ extern "C" {
> > extern void defer_rcu(void (*fct)(void *p), void *p);
> >
> > /*
> > - * call_rcu will eventually be implemented with an API similar to the Linux
> > - * kernel call_rcu(), which will allow its use within RCU read-side C.S.
> > - * Generate an error if used for now.
> > - */
> > -
> > -#define call_rcu __error_call_rcu_not_implemented_please_use_defer_rcu
> > -
> > -/*
> > * Thread registration for reclamation.
> > */
> > extern void rcu_defer_register_thread(void);
> > diff --git a/urcu/wfqueue-static.h b/urcu/wfqueue-static.h
> > index 30d6e96..a989f28 100644
> > --- a/urcu/wfqueue-static.h
> > +++ b/urcu/wfqueue-static.h
> > @@ -47,11 +47,17 @@ extern "C" {
> > #define WFQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
> > #define WFQ_WAIT 10 /* Wait 10 ms if being set */
> >
> > +#ifdef _LGPL_SOURCE
> > +static inline
> > +#endif /* #ifdef _LGPL_SOURCE */
>
> We should actually declare all these as "static inline" in every case, and
> create a little .c file in the urcu root to contain the wrapper stub library
> apps could link to. This would follow the same layout I've used for all the
> other code.
Let me make sure I understand what you are looking for here...
You want a urcu-call-rcu-static.h, which will contain the current
contents of urcu-call-rcu.c, but with all exported functions having
their names prefixed by "_". Then the new urcu-call-rcu.c has one
wrapper function per exported function, correct?
Thanx, Paul
> Thanks,
>
> Mathieu
>
> > void _cds_wfq_node_init(struct cds_wfq_node *node)
> > {
> > node->next = NULL;
> > }
> >
> > +#ifdef _LGPL_SOURCE
> > +static inline
> > +#endif /* #ifdef _LGPL_SOURCE */
> > void _cds_wfq_init(struct cds_wfq_queue *q)
> > {
> > int ret;
> > @@ -64,6 +70,9 @@ void _cds_wfq_init(struct cds_wfq_queue *q)
> > assert(!ret);
> > }
> >
> > +#ifdef _LGPL_SOURCE
> > +static inline
> > +#endif /* #ifdef _LGPL_SOURCE */
> > void _cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> > {
> > struct cds_wfq_node **old_tail;
> > @@ -90,6 +99,9 @@ void _cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> > * thread to be scheduled. The queue appears empty until tail->next is set by
> > * enqueue.
> > */
> > +#ifdef _LGPL_SOURCE
> > +static inline
> > +#endif /* #ifdef _LGPL_SOURCE */
> > struct cds_wfq_node *
> > ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > {
> > @@ -128,6 +140,9 @@ ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > return node;
> > }
> >
> > +#ifdef _LGPL_SOURCE
> > +static inline
> > +#endif /* #ifdef _LGPL_SOURCE */
> > struct cds_wfq_node *
> > _cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > {
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>
> _______________________________________________
> rp mailing list
> rp at svcs.cs.pdx.edu
> http://svcs.cs.pdx.edu/mailman/listinfo/rp
More information about the lttng-dev
mailing list