[ltt-dev] [URCU RFC patch 1/3] call_rcu: use cpu affinity for per-cpu call_rcu threads
Paul E. McKenney
paulmck at linux.vnet.ibm.com
Mon Jun 6 15:44:14 EDT 2011
On Mon, Jun 06, 2011 at 01:45:59PM -0400, Mathieu Desnoyers wrote:
> I played a bit with the call_rcu() implementation alongside with my
> rbtree tests, and noticed the following:
>
> If I use per-cpu call_rcu threads with URCU_CALL_RCU_RT flag, with one
> updater thread only for my rbtree (no reader), I get 38365 updates/s.
> If I add cpu affinity to these per-cpu call_rcu threads (I have prepared
> a patch that does this), it jumps to 54219 updates/s. So it looks like
> keeping per-cpu affinity for the call_rcu thread is a good thing.
Makes sense to me!
Main comment is that API.h should also be updated.
Thanx, Paul
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
> API.txt | 7 +++++--
> tests/rcutorture.h | 4 ++--
> urcu-call-rcu-impl.h | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
> urcu-call-rcu.h | 3 ++-
> urcu-qsbr.c | 1 +
> urcu.c | 1 +
> 6 files changed, 55 insertions(+), 12 deletions(-)
>
> Index: userspace-rcu/API.txt
> ===================================================================
> --- userspace-rcu.orig/API.txt
> +++ userspace-rcu/API.txt
> @@ -59,12 +59,15 @@ void call_rcu(struct rcu_head *head,
>
> call_rcu(&p->rcu, func);
>
> -struct call_rcu_data *create_call_rcu_data(unsigned long flags);
> +struct call_rcu_data *create_call_rcu_data(unsigned long flags,
> + int cpu_affinity);
>
> Returns a handle that can be passed to the following
> primitives. The "flags" argument can be zero, or can be
> URCU_CALL_RCU_RT if the worker threads associated with the
> - new helper thread are to get real-time response.
> + new helper thread are to get real-time response. The argument
> + "cpu_affinity" specifies a cpu on which the call_rcu thread should
> + be affined to. It is ignored if negative.
>
> struct call_rcu_data *get_default_call_rcu_data(void);
>
> Index: userspace-rcu/tests/rcutorture.h
> ===================================================================
> --- userspace-rcu.orig/tests/rcutorture.h
> +++ userspace-rcu/tests/rcutorture.h
> @@ -156,7 +156,7 @@ void *rcu_update_perf_test(void *arg)
> if ((random() & 0xf00) == 0) {
> struct call_rcu_data *crdp;
>
> - crdp = create_call_rcu_data(0);
> + crdp = create_call_rcu_data(0, -1);
> if (crdp != NULL) {
> fprintf(stderr,
> "Using per-thread call_rcu() worker.\n");
> @@ -385,7 +385,7 @@ void *rcu_fake_update_stress_test(void *
> if ((random() & 0xf00) == 0) {
> struct call_rcu_data *crdp;
>
> - crdp = create_call_rcu_data(0);
> + crdp = create_call_rcu_data(0, -1);
> if (crdp != NULL) {
> fprintf(stderr,
> "Using per-thread call_rcu() worker.\n");
> Index: userspace-rcu/urcu-call-rcu-impl.h
> ===================================================================
> --- userspace-rcu.orig/urcu-call-rcu-impl.h
> +++ userspace-rcu/urcu-call-rcu-impl.h
> @@ -20,6 +20,7 @@
> * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> */
>
> +#define _GNU_SOURCE
> #include <stdio.h>
> #include <pthread.h>
> #include <signal.h>
> @@ -31,6 +32,7 @@
> #include <sys/time.h>
> #include <syscall.h>
> #include <unistd.h>
> +#include <sched.h>
>
> #include "config.h"
> #include "urcu/wfqueue.h"
> @@ -47,6 +49,7 @@ struct call_rcu_data {
> pthread_cond_t cond;
> unsigned long qlen;
> pthread_t tid;
> + int cpu_affinity;
> struct cds_list_head list;
> } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
>
> @@ -146,6 +149,31 @@ static void call_rcu_unlock(pthread_mute
> }
> }
>
> +#if HAVE_SCHED_SETAFFINITY
> +static
> +int set_thread_cpu_affinity(struct call_rcu_data *crdp)
> +{
> + cpu_set_t mask;
> +
> + if (crdp->cpu_affinity < 0)
> + return 0;
> +
> + CPU_ZERO(&mask);
> + CPU_SET(crdp->cpu_affinity, &mask);
> +#if SCHED_SETAFFINITY_ARGS == 2
> + return sched_setaffinity(0, &mask);
> +#else
> + return sched_setaffinity(0, sizeof(mask), &mask);
> +#endif
> +}
> +#else
> +static
> +int set_thread_cpu_affinity(struct call_rcu_data *crdp)
> +{
> + return 0;
> +}
> +#endif
> +
> /* This is the code run by each call_rcu thread. */
>
> static void *call_rcu_thread(void *arg)
> @@ -156,6 +184,11 @@ static void *call_rcu_thread(void *arg)
> struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
> struct rcu_head *rhp;
>
> + if (set_thread_cpu_affinity(crdp) != 0) {
> + perror("pthread_setaffinity_np");
> + exit(-1);
> + }
> +
> thread_call_rcu_data = crdp;
> for (;;) {
> if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
> @@ -214,7 +247,8 @@ static void *call_rcu_thread(void *arg)
> */
>
> static void call_rcu_data_init(struct call_rcu_data **crdpp,
> - unsigned long flags)
> + unsigned long flags,
> + int cpu_affinity)
> {
> struct call_rcu_data *crdp;
>
> @@ -236,6 +270,7 @@ static void call_rcu_data_init(struct ca
> }
> crdp->flags = flags | URCU_CALL_RCU_RUNNING;
> cds_list_add(&crdp->list, &call_rcu_data_list);
> + crdp->cpu_affinity = cpu_affinity;
> cmm_smp_mb(); /* Structure initialized before pointer is planted. */
> *crdpp = crdp;
> if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
> @@ -280,20 +315,22 @@ pthread_t get_call_rcu_thread(struct cal
> * Create a call_rcu_data structure (with thread) and return a pointer.
> */
>
> -static struct call_rcu_data *__create_call_rcu_data(unsigned long flags)
> +static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
> + int cpu_affinity)
> {
> struct call_rcu_data *crdp;
>
> - call_rcu_data_init(&crdp, flags);
> + call_rcu_data_init(&crdp, flags, cpu_affinity);
> return crdp;
> }
>
> -struct call_rcu_data *create_call_rcu_data(unsigned long flags)
> +struct call_rcu_data *create_call_rcu_data(unsigned long flags,
> + int cpu_affinity)
> {
> struct call_rcu_data *crdp;
>
> call_rcu_lock(&call_rcu_mutex);
> - crdp = __create_call_rcu_data(flags);
> + crdp = __create_call_rcu_data(flags, cpu_affinity);
> call_rcu_unlock(&call_rcu_mutex);
> return crdp;
> }
> @@ -346,7 +383,7 @@ struct call_rcu_data *get_default_call_r
> call_rcu_unlock(&call_rcu_mutex);
> return default_call_rcu_data;
> }
> - call_rcu_data_init(&default_call_rcu_data, 0);
> + call_rcu_data_init(&default_call_rcu_data, 0, -1);
> call_rcu_unlock(&call_rcu_mutex);
> return default_call_rcu_data;
> }
> @@ -434,7 +471,7 @@ int create_all_cpu_call_rcu_data(unsigne
> call_rcu_unlock(&call_rcu_mutex);
> continue;
> }
> - crdp = __create_call_rcu_data(flags);
> + crdp = __create_call_rcu_data(flags, i);
> if (crdp == NULL) {
> call_rcu_unlock(&call_rcu_mutex);
> errno = ENOMEM;
> Index: userspace-rcu/urcu-call-rcu.h
> ===================================================================
> --- userspace-rcu.orig/urcu-call-rcu.h
> +++ userspace-rcu/urcu-call-rcu.h
> @@ -64,7 +64,8 @@ struct rcu_head {
> */
> 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);
> +struct call_rcu_data *create_call_rcu_data(unsigned long flags,
> + int cpu_affinity);
> 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);
> Index: userspace-rcu/urcu-qsbr.c
> ===================================================================
> --- userspace-rcu.orig/urcu-qsbr.c
> +++ userspace-rcu/urcu-qsbr.c
> @@ -23,6 +23,7 @@
> * IBM's contributions to this file may be relicensed under LGPLv2 or later.
> */
>
> +#define _GNU_SOURCE
> #include <stdio.h>
> #include <pthread.h>
> #include <signal.h>
> Index: userspace-rcu/urcu.c
> ===================================================================
> --- userspace-rcu.orig/urcu.c
> +++ userspace-rcu/urcu.c
> @@ -24,6 +24,7 @@
> */
>
> #define _BSD_SOURCE
> +#define _GNU_SOURCE
> #include <stdio.h>
> #include <pthread.h>
> #include <signal.h>
>
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