[PATCH tip/core/rcu 20/30] refperf: Add read-side delay module parameter

paulmck
2020-06-23T00:31:19Z

This commit adds a refperf.readdelay module parameter that controls the
duration of each critical section. This parameter allows gathering data
showing how the performance differences between the various primitives
vary with critical-section length.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/refperf.c | 108 ++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 89 insertions(+), 19 deletions(-)

diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c
index 7839237..57a750b 100644
--- a/kernel/rcu/refperf.c
+++ b/kernel/rcu/refperf.c
@@ -66,8 +66,8 @@ torture_param(long, loops, 10000000, "Number of loops per experiment.");
torture_param(int, nreaders, -1, "Number of readers, -1 for 75% of CPUs.");
// Number of runs.
torture_param(int, nruns, 30, "Number of experiments to run.");
-// Reader delay in nanoseconds, 0 for no delay.
-torture_param(int, readdelay, 0, "Read-side delay in nanoseconds.");
+// Reader delay in microseconds, 0 for no delay.
+torture_param(int, readdelay, 0, "Read-side delay in microseconds.");

#ifdef MODULE
# define REFPERF_SHUTDOWN 0
@@ -111,6 +111,7 @@ struct ref_perf_ops {
void (*init)(void);
void (*cleanup)(void);
void (*readsection)(const int nloops);
+ void (*delaysection)(const int nloops, const int ndelay);
const char *name;
};

@@ -126,6 +127,17 @@ static void ref_rcu_read_section(const int nloops)
}
}

+static void ref_rcu_delay_section(const int nloops, const int ndelay)
+{
+ int i;
+
+ for (i = nloops; i >= 0; i--) {
+ rcu_read_lock();
+ udelay(ndelay);
+ rcu_read_unlock();
+ }
+}
+
static void rcu_sync_perf_init(void)
{
}
@@ -133,6 +145,7 @@ static void rcu_sync_perf_init(void)
static struct ref_perf_ops rcu_ops = {
.init = rcu_sync_perf_init,
.readsection = ref_rcu_read_section,
+ .delaysection = ref_rcu_delay_section,
.name = "rcu"
};

@@ -141,7 +154,7 @@ static struct ref_perf_ops rcu_ops = {
DEFINE_STATIC_SRCU(srcu_refctl_perf);
static struct srcu_struct *srcu_ctlp = &srcu_refctl_perf;

-static void srcu_ref_perf_read_section(int nloops)
+static void srcu_ref_perf_read_section(const int nloops)
{
int i;
int idx;
@@ -152,16 +165,29 @@ static void srcu_ref_perf_read_section(int nloops)
}
}

+static void srcu_ref_perf_delay_section(const int nloops, const int ndelay)
+{
+ int i;
+ int idx;
+
+ for (i = nloops; i >= 0; i--) {
+ idx = srcu_read_lock(srcu_ctlp);
+ udelay(ndelay);
+ srcu_read_unlock(srcu_ctlp, idx);
+ }
+}
+
static struct ref_perf_ops srcu_ops = {
.init = rcu_sync_perf_init,
.readsection = srcu_ref_perf_read_section,
+ .delaysection = srcu_ref_perf_delay_section,
.name = "srcu"
};

// Definitions for reference count
static atomic_t refcnt;

-static void ref_perf_refcnt_section(const int nloops)
+static void ref_refcnt_section(const int nloops)
{
int i;

@@ -171,45 +197,69 @@ static void ref_perf_refcnt_section(const int nloops)
}
}

+static void ref_refcnt_delay_section(const int nloops, const int ndelay)
+{
+ int i;
+
+ for (i = nloops; i >= 0; i--) {
+ atomic_inc(&refcnt);
+ udelay(ndelay);
+ atomic_dec(&refcnt);
+ }
+}
+
static struct ref_perf_ops refcnt_ops = {
.init = rcu_sync_perf_init,
- .readsection = ref_perf_refcnt_section,
+ .readsection = ref_refcnt_section,
+ .delaysection = ref_refcnt_delay_section,
.name = "refcnt"
};

// Definitions for rwlock
static rwlock_t test_rwlock;

-static void ref_perf_rwlock_init(void)
+static void ref_rwlock_init(void)
{
rwlock_init(&test_rwlock);
}

-static void ref_perf_rwlock_section(const int nloops)
+static void ref_rwlock_section(const int nloops)
+{
+ int i;
+
+ for (i = nloops; i >= 0; i--) {
+ read_lock(&test_rwlock);
+ read_unlock(&test_rwlock);
+ }
+}
+
+static void ref_rwlock_delay_section(const int nloops, const int ndelay)
{
int i;

for (i = nloops; i >= 0; i--) {
read_lock(&test_rwlock);
+ udelay(ndelay);
read_unlock(&test_rwlock);
}
}

static struct ref_perf_ops rwlock_ops = {
- .init = ref_perf_rwlock_init,
- .readsection = ref_perf_rwlock_section,
+ .init = ref_rwlock_init,
+ .readsection = ref_rwlock_section,
+ .delaysection = ref_rwlock_delay_section,
.name = "rwlock"
};

// Definitions for rwsem
static struct rw_semaphore test_rwsem;

-static void ref_perf_rwsem_init(void)
+static void ref_rwsem_init(void)
{
init_rwsem(&test_rwsem);
}

-static void ref_perf_rwsem_section(const int nloops)
+static void ref_rwsem_section(const int nloops)
{
int i;

@@ -219,12 +269,32 @@ static void ref_perf_rwsem_section(const int nloops)
}
}

+static void ref_rwsem_delay_section(const int nloops, const int ndelay)
+{
+ int i;
+
+ for (i = nloops; i >= 0; i--) {
+ down_read(&test_rwsem);
+ udelay(ndelay);
+ up_read(&test_rwsem);
+ }
+}
+
static struct ref_perf_ops rwsem_ops = {
- .init = ref_perf_rwsem_init,
- .readsection = ref_perf_rwsem_section,
+ .init = ref_rwsem_init,
+ .readsection = ref_rwsem_section,
+ .delaysection = ref_rwsem_delay_section,
.name = "rwsem"
};

+static void rcu_perf_one_reader(void)
+{
+ if (readdelay <= 0)
+ cur_ops->readsection(loops);
+ else
+ cur_ops->delaysection(loops, readdelay);
+}
+
// Reader kthread. Repeatedly does empty RCU read-side
// critical section, minimizing update-side interference.
static int
@@ -265,16 +335,16 @@ ref_perf_reader(void *arg)

// To reduce noise, do an initial cache-warming invocation, check
// in, and then keep warming until everyone has checked in.
- cur_ops->readsection(loops);
+ rcu_perf_one_reader();
if (!atomic_dec_return(&n_warmedup))
while (atomic_read_acquire(&n_warmedup))
- cur_ops->readsection(loops);
+ rcu_perf_one_reader();
// Also keep interrupts disabled. This also has the effect
// of preventing entries into slow path for rcu_read_unlock().
local_irq_save(flags);
start = ktime_get_mono_fast_ns();

- cur_ops->readsection(loops);
+ rcu_perf_one_reader();

duration = ktime_get_mono_fast_ns() - start;
local_irq_restore(flags);
@@ -284,7 +354,7 @@ ref_perf_reader(void *arg)
// everyone is done.
if (!atomic_dec_return(&n_cooleddown))
while (atomic_read_acquire(&n_cooleddown))
- cur_ops->readsection(loops);
+ rcu_perf_one_reader();

if (atomic_dec_and_test(&nreaders_exp))
wake_up(&main_wq);
@@ -449,8 +519,8 @@ static void
ref_perf_print_module_parms(struct ref_perf_ops *cur_ops, const char *tag)
{
pr_alert("%s" PERF_FLAG
- "--- %s: verbose=%d shutdown=%d holdoff=%d loops=%ld nreaders=%d nruns=%d\n", perf_type, tag,
- verbose, shutdown, holdoff, loops, nreaders, nruns);
+ "--- %s: verbose=%d shutdown=%d holdoff=%d loops=%ld nreaders=%d nruns=%d readdelay=%d\n", perf_type, tag,
+ verbose, shutdown, holdoff, loops, nreaders, nruns, readdelay);
}

static void
--
2.9.5