diff options
Diffstat (limited to 'kernel/rcu/refscale.c')
| -rw-r--r-- | kernel/rcu/refscale.c | 717 |
1 files changed, 717 insertions, 0 deletions
diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c new file mode 100644 index 000000000000..d9291f883b54 --- /dev/null +++ b/kernel/rcu/refscale.c @@ -0,0 +1,717 @@ +// 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"); + + 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); |