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// SPDX-License-Identifier: GPL-2.0+
//
// Scalability test comparing RCU vs other mechanisms
// for acquiring references on objects.
//
// Copyright (C) Google, 2020.
//
// Author: Joel Fernandes <joel@joelfernandes.org>
#define pr_fmt(fmt) fmt
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/completion.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kthread.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/notifier.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/rcupdate_trace.h>
#include <linux/reboot.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/stat.h>
#include <linux/srcu.h>
#include <linux/slab.h>
#include <linux/torture.h>
#include <linux/types.h>
#include "rcu.h"
#define SCALE_FLAG "-ref-scale: "
#define SCALEOUT(s, x...) \
pr_alert("%s" SCALE_FLAG s, scale_type, ## x)
#define VERBOSE_SCALEOUT(s, x...) \
do { if (verbose) pr_alert("%s" SCALE_FLAG s, scale_type, ## x); } while (0)
#define VERBOSE_SCALEOUT_ERRSTRING(s, x...) \
do { if (verbose) pr_alert("%s" SCALE_FLAG "!!! " s, scale_type, ## x); } while (0)
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joel Fernandes (Google) <joel@joelfernandes.org>");
static char *scale_type = "rcu";
module_param(scale_type, charp, 0444);
MODULE_PARM_DESC(scale_type, "Type of test (rcu, srcu, refcnt, rwsem, rwlock.");
torture_param(int, verbose, 0, "Enable verbose debugging printk()s");
// Wait until there are multiple CPUs before starting test.
torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0,
"Holdoff time before test start (s)");
// Number of loops per experiment, all readers execute operations concurrently.
torture_param(long, loops, 10000, "Number of loops per experiment.");
// Number of readers, with -1 defaulting to about 75% of the CPUs.
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.");
#ifdef MODULE
# define REFSCALE_SHUTDOWN 0
#else
# define REFSCALE_SHUTDOWN 1
#endif
torture_param(bool, shutdown, REFSCALE_SHUTDOWN,
"Shutdown at end of scalability tests.");
struct reader_task {
struct task_struct *task;
int start_reader;
wait_queue_head_t wq;
u64 last_duration_ns;
};
static struct task_struct *shutdown_task;
static wait_queue_head_t shutdown_wq;
static struct task_struct *main_task;
static wait_queue_head_t main_wq;
static int shutdown_start;
static struct reader_task *reader_tasks;
// Number of readers that are part of the current experiment.
static atomic_t nreaders_exp;
// Use to wait for all threads to start.
static atomic_t n_init;
static atomic_t n_started;
static atomic_t n_warmedup;
static atomic_t n_cooleddown;
// Track which experiment is currently running.
static int exp_idx;
// Operations vector for selecting different types of tests.
struct ref_scale_ops {
void (*init)(void);
void (*cleanup)(void);
void (*readsection)(const int nloops);
void (*delaysection)(const int nloops, const int udl, const int ndl);
const char *name;
};
static struct ref_scale_ops *cur_ops;
static void un_delay(const int udl, const int ndl)
{
if (udl)
udelay(udl);
if (ndl)
ndelay(ndl);
}
static void ref_rcu_read_section(const int nloops)
{
int i;
for (i = nloops; i >= 0; i--) {
rcu_read_lock();
rcu_read_unlock();
}
}
static void ref_rcu_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--) {
rcu_read_lock();
un_delay(udl, ndl);
rcu_read_unlock();
}
}
static void rcu_sync_scale_init(void)
{
}
static struct ref_scale_ops rcu_ops = {
.init = rcu_sync_scale_init,
.readsection = ref_rcu_read_section,
.delaysection = ref_rcu_delay_section,
.name = "rcu"
};
// Definitions for SRCU ref scale testing.
DEFINE_STATIC_SRCU(srcu_refctl_scale);
static struct srcu_struct *srcu_ctlp = &srcu_refctl_scale;
static void srcu_ref_scale_read_section(const int nloops)
{
int i;
int idx;
for (i = nloops; i >= 0; i--) {
idx = srcu_read_lock(srcu_ctlp);
srcu_read_unlock(srcu_ctlp, idx);
}
}
static void srcu_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
int idx;
for (i = nloops; i >= 0; i--) {
idx = srcu_read_lock(srcu_ctlp);
un_delay(udl, ndl);
srcu_read_unlock(srcu_ctlp, idx);
}
}
static struct ref_scale_ops srcu_ops = {
.init = rcu_sync_scale_init,
.readsection = srcu_ref_scale_read_section,
.delaysection = srcu_ref_scale_delay_section,
.name = "srcu"
};
// Definitions for RCU Tasks ref scale testing: Empty read markers.
// These definitions also work for RCU Rude readers.
static void rcu_tasks_ref_scale_read_section(const int nloops)
{
int i;
for (i = nloops; i >= 0; i--)
continue;
}
static void rcu_tasks_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--)
un_delay(udl, ndl);
}
static struct ref_scale_ops rcu_tasks_ops = {
.init = rcu_sync_scale_init,
.readsection = rcu_tasks_ref_scale_read_section,
.delaysection = rcu_tasks_ref_scale_delay_section,
.name = "rcu-tasks"
};
// Definitions for RCU Tasks Trace ref scale testing.
static void rcu_trace_ref_scale_read_section(const int nloops)
{
int i;
for (i = nloops; i >= 0; i--) {
rcu_read_lock_trace();
rcu_read_unlock_trace();
}
}
static void rcu_trace_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--) {
rcu_read_lock_trace();
un_delay(udl, ndl);
rcu_read_unlock_trace();
}
}
static struct ref_scale_ops rcu_trace_ops = {
.init = rcu_sync_scale_init,
.readsection = rcu_trace_ref_scale_read_section,
.delaysection = rcu_trace_ref_scale_delay_section,
.name = "rcu-trace"
};
// Definitions for reference count
static atomic_t refcnt;
static void ref_refcnt_section(const int nloops)
{
int i;
for (i = nloops; i >= 0; i--) {
atomic_inc(&refcnt);
atomic_dec(&refcnt);
}
}
static void ref_refcnt_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--) {
atomic_inc(&refcnt);
un_delay(udl, ndl);
atomic_dec(&refcnt);
}
}
static struct ref_scale_ops refcnt_ops = {
.init = rcu_sync_scale_init,
.readsection = ref_refcnt_section,
.delaysection = ref_refcnt_delay_section,
.name = "refcnt"
};
// Definitions for rwlock
static rwlock_t test_rwlock;
static void ref_rwlock_init(void)
{
rwlock_init(&test_rwlock);
}
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 udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--) {
read_lock(&test_rwlock);
un_delay(udl, ndl);
read_unlock(&test_rwlock);
}
}
static struct ref_scale_ops rwlock_ops = {
.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_rwsem_init(void)
{
init_rwsem(&test_rwsem);
}
static void ref_rwsem_section(const int nloops)
{
int i;
for (i = nloops; i >= 0; i--) {
down_read(&test_rwsem);
up_read(&test_rwsem);
}
}
static void ref_rwsem_delay_section(const int nloops, const int udl, const int ndl)
{
int i;
for (i = nloops; i >= 0; i--) {
down_read(&test_rwsem);
un_delay(udl, ndl);
up_read(&test_rwsem);
}
}
static struct ref_scale_ops rwsem_ops = {
.init = ref_rwsem_init,
.readsection = ref_rwsem_section,
.delaysection = ref_rwsem_delay_section,
.name = "rwsem"
};
static void rcu_scale_one_reader(void)
{
if (readdelay <= 0)
cur_ops->readsection(loops);
else
cur_ops->delaysection(loops, readdelay / 1000, readdelay % 1000);
}
// Reader kthread. Repeatedly does empty RCU read-side
// critical section, minimizing update-side interference.
static int
ref_scale_reader(void *arg)
{
unsigned long flags;
long me = (long)arg;
struct reader_task *rt = &(reader_tasks[me]);
u64 start;
s64 duration;
VERBOSE_SCALEOUT("ref_scale_reader %ld: task started", me);
set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
set_user_nice(current, MAX_NICE);
atomic_inc(&n_init);
if (holdoff)
schedule_timeout_interruptible(holdoff * HZ);
repeat:
VERBOSE_SCALEOUT("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id());
// Wait for signal that this reader can start.
wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) ||
torture_must_stop());
if (torture_must_stop())
goto end;
// Make sure that the CPU is affinitized appropriately during testing.
WARN_ON_ONCE(smp_processor_id() != me);
WRITE_ONCE(rt->start_reader, 0);
if (!atomic_dec_return(&n_started))
while (atomic_read_acquire(&n_started))
cpu_relax();
VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d started", me, exp_idx);
// To reduce noise, do an initial cache-warming invocation, check
// in, and then keep warming until everyone has checked in.
rcu_scale_one_reader();
if (!atomic_dec_return(&n_warmedup))
while (atomic_read_acquire(&n_warmedup))
rcu_scale_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();
rcu_scale_one_reader();
duration = ktime_get_mono_fast_ns() - start;
local_irq_restore(flags);
rt->last_duration_ns = WARN_ON_ONCE(duration < 0) ? 0 : duration;
// To reduce runtime-skew noise, do maintain-load invocations until
// everyone is done.
if (!atomic_dec_return(&n_cooleddown))
while (atomic_read_acquire(&n_cooleddown))
rcu_scale_one_reader();
if (atomic_dec_and_test(&nreaders_exp))
wake_up(&main_wq);
VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)",
me, exp_idx, atomic_read(&nreaders_exp));
if (!torture_must_stop())
goto repeat;
end:
torture_kthread_stopping("ref_scale_reader");
return 0;
}
static void reset_readers(void)
{
int i;
struct reader_task *rt;
for (i = 0; i < nreaders; i++) {
rt = &(reader_tasks[i]);
rt->last_duration_ns = 0;
}
}
// Print the results of each reader and return the sum of all their durations.
static u64 process_durations(int n)
{
int i;
struct reader_task *rt;
char buf1[64];
char *buf;
u64 sum = 0;
buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
if (!buf)
return 0;
buf[0] = 0;
sprintf(buf, "Experiment #%d (Format: <THREAD-NUM>:<Total loop time in ns>)",
exp_idx);
for (i = 0; i < n && !torture_must_stop(); i++) {
rt = &(reader_tasks[i]);
sprintf(buf1, "%d: %llu\t", i, rt->last_duration_ns);
if (i % 5 == 0)
strcat(buf, "\n");
strcat(buf, buf1);
sum += rt->last_duration_ns;
}
strcat(buf, "\n");
SCALEOUT("%s\n", buf);
kfree(buf);
return sum;
}
// The main_func is the main orchestrator, it performs a bunch of
// experiments. For every experiment, it orders all the readers
// involved to start and waits for them to finish the experiment. It
// then reads their timestamps and starts the next experiment. Each
// experiment progresses from 1 concurrent reader to N of them at which
// point all the timestamps are printed.
static int main_func(void *arg)
{
bool errexit = false;
int exp, r;
char buf1[64];
char *buf;
u64 *result_avg;
set_cpus_allowed_ptr(current, cpumask_of(nreaders % nr_cpu_ids));
set_user_nice(current, MAX_NICE);
VERBOSE_SCALEOUT("main_func task started");
result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
if (!result_avg || !buf) {
VERBOSE_SCALEOUT_ERRSTRING("out of memory");
errexit = true;
}
if (holdoff)
schedule_timeout_interruptible(holdoff * HZ);
// Wait for all threads to start.
atomic_inc(&n_init);
while (atomic_read(&n_init) < nreaders + 1)
schedule_timeout_uninterruptible(1);
// Start exp readers up per experiment
for (exp = 0; exp < nruns && !torture_must_stop(); exp++) {
if (errexit)
break;
if (torture_must_stop())
goto end;
reset_readers();
atomic_set(&nreaders_exp, nreaders);
atomic_set(&n_started, nreaders);
atomic_set(&n_warmedup, nreaders);
atomic_set(&n_cooleddown, nreaders);
exp_idx = exp;
for (r = 0; r < nreaders; r++) {
smp_store_release(&reader_tasks[r].start_reader, 1);
wake_up(&reader_tasks[r].wq);
}
VERBOSE_SCALEOUT("main_func: experiment started, waiting for %d readers",
nreaders);
wait_event(main_wq,
!atomic_read(&nreaders_exp) || torture_must_stop());
VERBOSE_SCALEOUT("main_func: experiment ended");
if (torture_must_stop())
goto end;
result_avg[exp] = div_u64(1000 * process_durations(nreaders), nreaders * loops);
}
// Print the average of all experiments
SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n");
if (!errexit) {
buf[0] = 0;
strcat(buf, "\n");
strcat(buf, "Runs\tTime(ns)\n");
}
for (exp = 0; exp < nruns; exp++) {
u64 avg;
u32 rem;
if (errexit)
break;
avg = div_u64_rem(result_avg[exp], 1000, &rem);
sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
strcat(buf, buf1);
}
if (!errexit)
SCALEOUT("%s", buf);
// This will shutdown everything including us.
if (shutdown) {
shutdown_start = 1;
wake_up(&shutdown_wq);
}
// Wait for torture to stop us
while (!torture_must_stop())
schedule_timeout_uninterruptible(1);
end:
torture_kthread_stopping("main_func");
kfree(result_avg);
kfree(buf);
return 0;
}
static void
ref_scale_print_module_parms(struct ref_scale_ops *cur_ops, const char *tag)
{
pr_alert("%s" SCALE_FLAG
"--- %s: verbose=%d shutdown=%d holdoff=%d loops=%ld nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
verbose, shutdown, holdoff, loops, nreaders, nruns, readdelay);
}
static void
ref_scale_cleanup(void)
{
int i;
if (torture_cleanup_begin())
return;
if (!cur_ops) {
torture_cleanup_end();
return;
}
if (reader_tasks) {
for (i = 0; i < nreaders; i++)
torture_stop_kthread("ref_scale_reader",
reader_tasks[i].task);
}
kfree(reader_tasks);
torture_stop_kthread("main_task", main_task);
kfree(main_task);
// Do scale-type-specific cleanup operations.
if (cur_ops->cleanup != NULL)
cur_ops->cleanup();
torture_cleanup_end();
}
// Shutdown kthread. Just waits to be awakened, then shuts down system.
static int
ref_scale_shutdown(void *arg)
{
wait_event(shutdown_wq, shutdown_start);
smp_mb(); // Wake before output.
ref_scale_cleanup();
kernel_power_off();
return -EINVAL;
}
static int __init
ref_scale_init(void)
{
long i;
int firsterr = 0;
static struct ref_scale_ops *scale_ops[] = {
&rcu_ops, &srcu_ops, &rcu_trace_ops, &rcu_tasks_ops,
&refcnt_ops, &rwlock_ops, &rwsem_ops,
};
if (!torture_init_begin(scale_type, verbose))
return -EBUSY;
for (i = 0; i < ARRAY_SIZE(scale_ops); i++) {
cur_ops = scale_ops[i];
if (strcmp(scale_type, cur_ops->name) == 0)
break;
}
if (i == ARRAY_SIZE(scale_ops)) {
pr_alert("rcu-scale: invalid scale type: \"%s\"\n", scale_type);
pr_alert("rcu-scale types:");
for (i = 0; i < ARRAY_SIZE(scale_ops); i++)
pr_cont(" %s", scale_ops[i]->name);
pr_cont("\n");
WARN_ON(!IS_MODULE(CONFIG_RCU_REF_SCALE_TEST));
firsterr = -EINVAL;
cur_ops = NULL;
goto unwind;
}
if (cur_ops->init)
cur_ops->init();
ref_scale_print_module_parms(cur_ops, "Start of test");
// Shutdown task
if (shutdown) {
init_waitqueue_head(&shutdown_wq);
firsterr = torture_create_kthread(ref_scale_shutdown, NULL,
shutdown_task);
if (firsterr)
goto unwind;
schedule_timeout_uninterruptible(1);
}
// Reader tasks (default to ~75% of online CPUs).
if (nreaders < 0)
nreaders = (num_online_cpus() >> 1) + (num_online_cpus() >> 2);
reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]),
GFP_KERNEL);
if (!reader_tasks) {
VERBOSE_SCALEOUT_ERRSTRING("out of memory");
firsterr = -ENOMEM;
goto unwind;
}
VERBOSE_SCALEOUT("Starting %d reader threads\n", nreaders);
for (i = 0; i < nreaders; i++) {
firsterr = torture_create_kthread(ref_scale_reader, (void *)i,
reader_tasks[i].task);
if (firsterr)
goto unwind;
init_waitqueue_head(&(reader_tasks[i].wq));
}
// Main Task
init_waitqueue_head(&main_wq);
firsterr = torture_create_kthread(main_func, NULL, main_task);
if (firsterr)
goto unwind;
torture_init_end();
return 0;
unwind:
torture_init_end();
ref_scale_cleanup();
return firsterr;
}
module_init(ref_scale_init);
module_exit(ref_scale_cleanup);