Of late, the scheduler seems to have decided to make things too easy for
RCU -- on some configurations, all of the rcutorture tasks end up on the
same CPU, which doesn't do a very good job of torturing RCU. This patch
helps the scheduler spread these tasks out by forcing a 20-millisecond
burst of CPU-bound execution on each of rcutorture's tasks, which seems
to work reasonably well in practice.
My challenge for those working on the scheduler is to make this patch
unnecessary. ;-)
Signed-off-by: Paul E. McKenney <[email protected]>
---
rcutorture.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff -urpNa -X dontdiff linux-2.6.21.4-rt13/kernel/rcutorture.c linux-2.6.21.4-rt13-rcutorturespread/kernel/rcutorture.c
--- linux-2.6.21.4-rt13/kernel/rcutorture.c 2007-06-12 09:19:02.000000000 -0700
+++ linux-2.6.21.4-rt13-rcutorturespread/kernel/rcutorture.c 2007-06-12 21:05:05.000000000 -0700
@@ -102,6 +102,8 @@ struct rcu_torture {
};
static int fullstop = 0; /* stop generating callbacks at test end. */
+static int startwriters; /* force load-balancing of writers. */
+static int startreaders; /* force load-balancing of readers. */
static LIST_HEAD(rcu_torture_freelist);
static struct rcu_torture *rcu_torture_current = NULL;
static long rcu_torture_current_version = 0;
@@ -525,6 +527,8 @@ rcu_torture_writer(void *arg)
static DEFINE_RCU_RANDOM(rand);
VERBOSE_PRINTK_STRING("rcu_torture_writer task started");
+ while (!startwriters)
+ barrier(); /* Force scheduler to spread over CPUs. */
set_user_nice(current, 19);
current->flags |= PF_NOFREEZE;
@@ -565,6 +569,8 @@ rcu_torture_fakewriter(void *arg)
DEFINE_RCU_RANDOM(rand);
VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
+ while (!startwriters)
+ barrier(); /* Force scheduler to spread over CPUs. */
set_user_nice(current, 19);
current->flags |= PF_NOFREEZE;
@@ -596,6 +602,8 @@ rcu_torture_reader(void *arg)
int pipe_count;
VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
+ while (!startreaders)
+ barrier(); /* Force scheduler to spread over CPUs. */
set_user_nice(current, 19);
current->flags |= PF_NOFREEZE;
@@ -929,6 +937,8 @@ rcu_torture_init(void)
/* Start up the kthreads. */
+ startwriters = 0;
+ barrier();
VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
writer_task = kthread_run(rcu_torture_writer, NULL,
"rcu_torture_writer");
@@ -956,6 +966,12 @@ rcu_torture_init(void)
goto unwind;
}
}
+ barrier();
+ startwriters = 1;
+ schedule_timeout_interruptible(round_jiffies_relative(HZ/50));
+
+ startreaders = 0;
+ barrier();
reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
GFP_KERNEL);
if (reader_tasks == NULL) {
@@ -974,6 +990,10 @@ rcu_torture_init(void)
goto unwind;
}
}
+ schedule_timeout_interruptible(round_jiffies_relative(HZ/50));
+ barrier();
+ startreaders = 1;
+
if (stat_interval > 0) {
VERBOSE_PRINTK_STRING("Creating rcu_torture_stats task");
stats_task = kthread_run(rcu_torture_stats, NULL,
-
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