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Message-ID: <20070129021126.GA8417@linux.vnet.ibm.com>
Date: Sun, 28 Jan 2007 18:11:26 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Josh Triplett <josh@...nel.org>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...uxtronix.de,
dipankar@...ibm.com, tytso@...ibm.com, dvhltc@...ibm.com,
oleg@...sign.ru, twoerner.k@...il.com, billh@...ppy.monkey.org,
nielsen.esben@...glemail.com, corbet@....net
Subject: Re: [RFC PATCH -rt 2/2] RCU priority boosting additions to rcutorture
On Thu, Jan 25, 2007 at 11:06:35AM -0800, Josh Triplett wrote:
> Paul E. McKenney wrote:
> > On Thu, Jan 25, 2007 at 12:47:04AM -0800, Josh Triplett wrote:
> >> One major item: this new test feature really needs a new module parameter to
> >> enable or disable it.
> >
> > CONFIG_PREEMPT_RCU_BOOST is the parameter -- if not set, then no test.
> > This parameter is provided by the accompanying RCU-boost patch.
>
> It seems useful for rcutorture to use or not use the preempting thread
> independently of CONFIG_PREEMPT_RCU_BOOST. That would bring you from two
> cases to four, and the two new cases both make sense:
>
> * CONFIG_PREEMPT_RCU_BOOST=n, but run rcutorture with the preempting thread.
> This configuration allows you to demonstrate the need for
> CONFIG_PREEMPT_RCU_BOOST, by showing what happens when you need it and don't
> have it.
>
> * CONFIG_PREEMPT_RCU_BOOST=y, but run rcutorture without the preempting
> thread. This configuration allows you to test with rcutorture while running
> a *real* real-time workload rather than the simple preempting thread, or
> just test basic RCU functionality.
>
> A simple boolean module_param would work here.
OK, am finally with you. See below for updated patch.
> At some point, we may want to add the ability to run multiple preempting
> threads, but that doesn't need to happen for this patch.
Or to make it bounce around onto multiple CPUs, I suppose. Leaving
these out for the moment. ;-)
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
rcutorture.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 76 insertions(+), 14 deletions(-)
diff -urpNa -X dontdiff linux-2.6.20-rc4-rt1/kernel/rcutorture.c linux-2.6.20-rc4-rt1-rcubtorture/kernel/rcutorture.c
--- linux-2.6.20-rc4-rt1/kernel/rcutorture.c 2007-01-09 10:59:54.000000000 -0800
+++ linux-2.6.20-rc4-rt1-rcubtorture/kernel/rcutorture.c 2007-01-26 22:16:13.000000000 -0800
@@ -58,6 +58,7 @@ static int stat_interval; /* Interval be
static int verbose; /* Print more debug info. */
static int test_no_idle_hz; /* Test RCU's support for tickless idle CPUs. */
static int shuffle_interval = 5; /* Interval between shuffles (in sec)*/
+static int preempt_torture = 0; /* Realtime task preempts torture readers. */
static char *torture_type = "rcu"; /* What RCU implementation to torture. */
module_param(nreaders, int, 0);
@@ -72,6 +73,8 @@ module_param(test_no_idle_hz, bool, 0);
MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
module_param(shuffle_interval, int, 0);
MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
+module_param(preempt_torture, bool, 0);
+MODULE_PARM_DESC(preempt_torture, "Enable realtime preemption torture");
module_param(torture_type, charp, 0);
MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)");
@@ -194,6 +197,8 @@ struct rcu_torture_ops {
int (*completed)(void);
void (*deferredfree)(struct rcu_torture *p);
void (*sync)(void);
+ long (*preemptstart)(void);
+ void (*preemptend)(void);
int (*stats)(char *page);
char *name;
};
@@ -258,16 +263,74 @@ static void rcu_torture_deferred_free(st
call_rcu(&p->rtort_rcu, rcu_torture_cb);
}
+static struct task_struct *rcu_preeempt_task;
+static unsigned long rcu_torture_preempt_errors = 0;
+
+static int rcu_torture_preempt(void *arg)
+{
+ int completedstart;
+ int err;
+ time_t gcstart;
+ struct sched_param sp;
+
+ sp.sched_priority = MAX_RT_PRIO - 1;
+ err = sched_setscheduler(current, SCHED_RR, &sp);
+ if (err != 0)
+ printk(KERN_ALERT "rcu_torture_preempt() priority err: %d\n",
+ err);
+ current->flags |= PF_NOFREEZE;
+
+ do {
+ completedstart = rcu_torture_completed();
+ gcstart = xtime.tv_sec;
+ while ((xtime.tv_sec - gcstart < 10) &&
+ (rcu_torture_completed() == completedstart))
+ cond_resched();
+ if (rcu_torture_completed() == completedstart)
+ rcu_torture_preempt_errors++;
+ schedule_timeout_interruptible(HZ);
+ } while (!kthread_should_stop());
+ return NULL;
+}
+
+static long rcu_preempt_start(void)
+{
+ long retval = 0;
+
+ rcu_preeempt_task = kthread_run(rcu_torture_preempt, NULL,
+ "rcu_torture_preempt");
+ if (IS_ERR(rcu_preeempt_task)) {
+ VERBOSE_PRINTK_ERRSTRING("Failed to create preempter");
+ retval = PTR_ERR(rcu_preeempt_task);
+ rcu_preeempt_task = NULL;
+ }
+ return retval;
+}
+
+static void rcu_preempt_end(void)
+{
+ if (rcu_preeempt_task != NULL) {
+ VERBOSE_PRINTK_STRING("Stopping rcu_preempt task");
+ kthread_stop(rcu_preeempt_task);
+ }
+ rcu_preeempt_task = NULL;
+}
+
+static int rcu_preempt_stats(char *page) {
+ return sprintf(page,
+ "Preemption stalls: %lu\n", rcu_torture_preempt_errors);
+}
+
static struct rcu_torture_ops rcu_ops = {
- .init = NULL,
- .cleanup = NULL,
.readlock = rcu_torture_read_lock,
.readdelay = rcu_read_delay,
.readunlock = rcu_torture_read_unlock,
.completed = rcu_torture_completed,
.deferredfree = rcu_torture_deferred_free,
.sync = synchronize_rcu,
- .stats = NULL,
+ .preemptstart = rcu_preempt_start,
+ .preemptend = rcu_preempt_end,
+ .stats = rcu_preempt_stats,
.name = "rcu"
};
@@ -299,14 +362,12 @@ static void rcu_sync_torture_init(void)
static struct rcu_torture_ops rcu_sync_ops = {
.init = rcu_sync_torture_init,
- .cleanup = NULL,
.readlock = rcu_torture_read_lock,
.readdelay = rcu_read_delay,
.readunlock = rcu_torture_read_unlock,
.completed = rcu_torture_completed,
.deferredfree = rcu_sync_torture_deferred_free,
.sync = synchronize_rcu,
- .stats = NULL,
.name = "rcu_sync"
};
@@ -362,28 +423,23 @@ static void rcu_bh_torture_synchronize(v
}
static struct rcu_torture_ops rcu_bh_ops = {
- .init = NULL,
- .cleanup = NULL,
.readlock = rcu_bh_torture_read_lock,
.readdelay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = rcu_bh_torture_read_unlock,
.completed = rcu_bh_torture_completed,
.deferredfree = rcu_bh_torture_deferred_free,
.sync = rcu_bh_torture_synchronize,
- .stats = NULL,
.name = "rcu_bh"
};
static struct rcu_torture_ops rcu_bh_sync_ops = {
.init = rcu_sync_torture_init,
- .cleanup = NULL,
.readlock = rcu_bh_torture_read_lock,
.readdelay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = rcu_bh_torture_read_unlock,
.completed = rcu_bh_torture_completed,
.deferredfree = rcu_sync_torture_deferred_free,
.sync = rcu_bh_torture_synchronize,
- .stats = NULL,
.name = "rcu_bh_sync"
};
@@ -495,14 +551,12 @@ static void sched_torture_synchronize(vo
static struct rcu_torture_ops sched_ops = {
.init = rcu_sync_torture_init,
- .cleanup = NULL,
.readlock = sched_torture_read_lock,
.readdelay = rcu_read_delay, /* just reuse rcu's version. */
.readunlock = sched_torture_read_unlock,
.completed = sched_torture_completed,
.deferredfree = rcu_sync_torture_deferred_free,
.sync = sched_torture_synchronize,
- .stats = NULL,
.name = "sched"
};
@@ -801,9 +855,10 @@ rcu_torture_print_module_parms(char *tag
printk(KERN_ALERT "%s" TORTURE_FLAG
"--- %s: nreaders=%d nfakewriters=%d "
"stat_interval=%d verbose=%d test_no_idle_hz=%d "
- "shuffle_interval = %d\n",
+ "shuffle_interval=%d preempt_torture=%d\n",
torture_type, tag, nrealreaders, nfakewriters,
- stat_interval, verbose, test_no_idle_hz, shuffle_interval);
+ stat_interval, verbose, test_no_idle_hz, shuffle_interval,
+ preempt_torture);
}
static void
@@ -856,6 +911,8 @@ rcu_torture_cleanup(void)
kthread_stop(stats_task);
}
stats_task = NULL;
+ if (preempt_torture && (cur_ops->preemptend != NULL))
+ cur_ops->preemptend();
/* Wait for all RCU callbacks to fire. */
rcu_barrier();
@@ -997,6 +1054,11 @@ rcu_torture_init(void)
goto unwind;
}
}
+ if (preempt_torture && (cur_ops->preemptstart != NULL)) {
+ firsterr = cur_ops->preemptstart();
+ if (firsterr != 0)
+ goto unwind;
+ }
return 0;
unwind:
-
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