drm/rockchip: vop2: Support 32x8 superblock afbc

[drm/drm-misc.git] / kernel / rcu / refscale.c

// 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/seq_buf.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 "\n", scale_type, ## x); \
        } while (0)

static atomic_t verbose_batch_ctr;

#define VERBOSE_SCALEOUT_BATCH(s, x...)                                                 \
do {                                                                                    \
        if (verbose &&                                                                  \
            (verbose_batched <= 0 ||                                                    \
             !(atomic_inc_return(&verbose_batch_ctr) % verbose_batched))) {             \
                schedule_timeout_uninterruptible(1);                                    \
                pr_alert("%s" SCALE_FLAG s "\n", scale_type, ## x);                     \
        }                                                                               \
} while (0)

#define SCALEOUT_ERRSTRING(s, x...) pr_alert("%s" SCALE_FLAG "!!! " s "\n", scale_type, ## x)

MODULE_DESCRIPTION("Scalability test for object reference mechanisms");
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");
torture_param(int, verbose_batched, 0, "Batch verbose debugging printk()s");

// Number of seconds to extend warm-up and cool-down for multiple guest OSes
torture_param(long, guest_os_delay, 0,
              "Number of seconds to extend warm-up/cool-down for multiple guest OSes.");
// 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 typesafe_lookup structures, that is, the degree of concurrency.
torture_param(long, lookup_instances, 0, "Number of typesafe_lookup structures.");
// 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 {
        bool (*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 const 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 bool rcu_sync_scale_init(void)
{
        return true;
}

static const 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 const 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"
};

static void srcu_lite_ref_scale_read_section(const int nloops)
{
        int i;
        int idx;

        for (i = nloops; i >= 0; i--) {
                idx = srcu_read_lock_lite(srcu_ctlp);
                srcu_read_unlock_lite(srcu_ctlp, idx);
        }
}

static void srcu_lite_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_lite(srcu_ctlp);
                un_delay(udl, ndl);
                srcu_read_unlock_lite(srcu_ctlp, idx);
        }
}

static const struct ref_scale_ops srcu_lite_ops = {
        .init           = rcu_sync_scale_init,
        .readsection    = srcu_lite_ref_scale_read_section,
        .delaysection   = srcu_lite_ref_scale_delay_section,
        .name           = "srcu-lite"
};

#ifdef CONFIG_TASKS_RCU

// 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 const 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"
};

#define RCU_TASKS_OPS &rcu_tasks_ops,

#else // #ifdef CONFIG_TASKS_RCU

#define RCU_TASKS_OPS

#endif // #else // #ifdef CONFIG_TASKS_RCU

#ifdef CONFIG_TASKS_TRACE_RCU

// 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 const 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"
};

#define RCU_TRACE_OPS &rcu_trace_ops,

#else // #ifdef CONFIG_TASKS_TRACE_RCU

#define RCU_TRACE_OPS

#endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU

// 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 const 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 bool ref_rwlock_init(void)
{
        rwlock_init(&test_rwlock);
        return true;
}

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 const 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 bool ref_rwsem_init(void)
{
        init_rwsem(&test_rwsem);
        return true;
}

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 const struct ref_scale_ops rwsem_ops = {
        .init           = ref_rwsem_init,
        .readsection    = ref_rwsem_section,
        .delaysection   = ref_rwsem_delay_section,
        .name           = "rwsem"
};

// Definitions for global spinlock
static DEFINE_RAW_SPINLOCK(test_lock);

static void ref_lock_section(const int nloops)
{
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                raw_spin_lock(&test_lock);
                raw_spin_unlock(&test_lock);
        }
        preempt_enable();
}

static void ref_lock_delay_section(const int nloops, const int udl, const int ndl)
{
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                raw_spin_lock(&test_lock);
                un_delay(udl, ndl);
                raw_spin_unlock(&test_lock);
        }
        preempt_enable();
}

static const struct ref_scale_ops lock_ops = {
        .readsection    = ref_lock_section,
        .delaysection   = ref_lock_delay_section,
        .name           = "lock"
};

// Definitions for global irq-save spinlock

static void ref_lock_irq_section(const int nloops)
{
        unsigned long flags;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                raw_spin_lock_irqsave(&test_lock, flags);
                raw_spin_unlock_irqrestore(&test_lock, flags);
        }
        preempt_enable();
}

static void ref_lock_irq_delay_section(const int nloops, const int udl, const int ndl)
{
        unsigned long flags;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                raw_spin_lock_irqsave(&test_lock, flags);
                un_delay(udl, ndl);
                raw_spin_unlock_irqrestore(&test_lock, flags);
        }
        preempt_enable();
}

static const struct ref_scale_ops lock_irq_ops = {
        .readsection    = ref_lock_irq_section,
        .delaysection   = ref_lock_irq_delay_section,
        .name           = "lock-irq"
};

// Definitions acquire-release.
static DEFINE_PER_CPU(unsigned long, test_acqrel);

static void ref_acqrel_section(const int nloops)
{
        unsigned long x;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                x = smp_load_acquire(this_cpu_ptr(&test_acqrel));
                smp_store_release(this_cpu_ptr(&test_acqrel), x + 1);
        }
        preempt_enable();
}

static void ref_acqrel_delay_section(const int nloops, const int udl, const int ndl)
{
        unsigned long x;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                x = smp_load_acquire(this_cpu_ptr(&test_acqrel));
                un_delay(udl, ndl);
                smp_store_release(this_cpu_ptr(&test_acqrel), x + 1);
        }
        preempt_enable();
}

static const struct ref_scale_ops acqrel_ops = {
        .readsection    = ref_acqrel_section,
        .delaysection   = ref_acqrel_delay_section,
        .name           = "acqrel"
};

static volatile u64 stopopts;

static void ref_clock_section(const int nloops)
{
        u64 x = 0;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--)
                x += ktime_get_real_fast_ns();
        preempt_enable();
        stopopts = x;
}

static void ref_clock_delay_section(const int nloops, const int udl, const int ndl)
{
        u64 x = 0;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                x += ktime_get_real_fast_ns();
                un_delay(udl, ndl);
        }
        preempt_enable();
        stopopts = x;
}

static const struct ref_scale_ops clock_ops = {
        .readsection    = ref_clock_section,
        .delaysection   = ref_clock_delay_section,
        .name           = "clock"
};

static void ref_jiffies_section(const int nloops)
{
        u64 x = 0;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--)
                x += jiffies;
        preempt_enable();
        stopopts = x;
}

static void ref_jiffies_delay_section(const int nloops, const int udl, const int ndl)
{
        u64 x = 0;
        int i;

        preempt_disable();
        for (i = nloops; i >= 0; i--) {
                x += jiffies;
                un_delay(udl, ndl);
        }
        preempt_enable();
        stopopts = x;
}

static const struct ref_scale_ops jiffies_ops = {
        .readsection    = ref_jiffies_section,
        .delaysection   = ref_jiffies_delay_section,
        .name           = "jiffies"
};

////////////////////////////////////////////////////////////////////////
//
// Methods leveraging SLAB_TYPESAFE_BY_RCU.
//

// Item to look up in a typesafe manner.  Array of pointers to these.
struct refscale_typesafe {
        atomic_t rts_refctr;  // Used by all flavors
        spinlock_t rts_lock;
        seqlock_t rts_seqlock;
        unsigned int a;
        unsigned int b;
};

static struct kmem_cache *typesafe_kmem_cachep;
static struct refscale_typesafe **rtsarray;
static long rtsarray_size;
static DEFINE_TORTURE_RANDOM_PERCPU(refscale_rand);
static bool (*rts_acquire)(struct refscale_typesafe *rtsp, unsigned int *start);
static bool (*rts_release)(struct refscale_typesafe *rtsp, unsigned int start);

// Conditionally acquire an explicit in-structure reference count.
static bool typesafe_ref_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
{
        return atomic_inc_not_zero(&rtsp->rts_refctr);
}

// Unconditionally release an explicit in-structure reference count.
static bool typesafe_ref_release(struct refscale_typesafe *rtsp, unsigned int start)
{
        if (!atomic_dec_return(&rtsp->rts_refctr)) {
                WRITE_ONCE(rtsp->a, rtsp->a + 1);
                kmem_cache_free(typesafe_kmem_cachep, rtsp);
        }
        return true;
}

// Unconditionally acquire an explicit in-structure spinlock.
static bool typesafe_lock_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
{
        spin_lock(&rtsp->rts_lock);
        return true;
}

// Unconditionally release an explicit in-structure spinlock.
static bool typesafe_lock_release(struct refscale_typesafe *rtsp, unsigned int start)
{
        spin_unlock(&rtsp->rts_lock);
        return true;
}

// Unconditionally acquire an explicit in-structure sequence lock.
static bool typesafe_seqlock_acquire(struct refscale_typesafe *rtsp, unsigned int *start)
{
        *start = read_seqbegin(&rtsp->rts_seqlock);
        return true;
}

// Conditionally release an explicit in-structure sequence lock.  Return
// true if this release was successful, that is, if no retry is required.
static bool typesafe_seqlock_release(struct refscale_typesafe *rtsp, unsigned int start)
{
        return !read_seqretry(&rtsp->rts_seqlock, start);
}

// Do a read-side critical section with the specified delay in
// microseconds and nanoseconds inserted so as to increase probability
// of failure.
static void typesafe_delay_section(const int nloops, const int udl, const int ndl)
{
        unsigned int a;
        unsigned int b;
        int i;
        long idx;
        struct refscale_typesafe *rtsp;
        unsigned int start;

        for (i = nloops; i >= 0; i--) {
                preempt_disable();
                idx = torture_random(this_cpu_ptr(&refscale_rand)) % rtsarray_size;
                preempt_enable();
retry:
                rcu_read_lock();
                rtsp = rcu_dereference(rtsarray[idx]);
                a = READ_ONCE(rtsp->a);
                if (!rts_acquire(rtsp, &start)) {
                        rcu_read_unlock();
                        goto retry;
                }
                if (a != READ_ONCE(rtsp->a)) {
                        (void)rts_release(rtsp, start);
                        rcu_read_unlock();
                        goto retry;
                }
                un_delay(udl, ndl);
                b = READ_ONCE(rtsp->a);
                // Remember, seqlock read-side release can fail.
                if (!rts_release(rtsp, start)) {
                        rcu_read_unlock();
                        goto retry;
                }
                WARN_ONCE(a != b, "Re-read of ->a changed from %u to %u.\n", a, b);
                b = rtsp->b;
                rcu_read_unlock();
                WARN_ON_ONCE(a * a != b);
        }
}

// Because the acquisition and release methods are expensive, there
// is no point in optimizing away the un_delay() function's two checks.
// Thus simply define typesafe_read_section() as a simple wrapper around
// typesafe_delay_section().
static void typesafe_read_section(const int nloops)
{
        typesafe_delay_section(nloops, 0, 0);
}

// Allocate and initialize one refscale_typesafe structure.
static struct refscale_typesafe *typesafe_alloc_one(void)
{
        struct refscale_typesafe *rtsp;

        rtsp = kmem_cache_alloc(typesafe_kmem_cachep, GFP_KERNEL);
        if (!rtsp)
                return NULL;
        atomic_set(&rtsp->rts_refctr, 1);
        WRITE_ONCE(rtsp->a, rtsp->a + 1);
        WRITE_ONCE(rtsp->b, rtsp->a * rtsp->a);
        return rtsp;
}

// Slab-allocator constructor for refscale_typesafe structures created
// out of a new slab of system memory.
static void refscale_typesafe_ctor(void *rtsp_in)
{
        struct refscale_typesafe *rtsp = rtsp_in;

        spin_lock_init(&rtsp->rts_lock);
        seqlock_init(&rtsp->rts_seqlock);
        preempt_disable();
        rtsp->a = torture_random(this_cpu_ptr(&refscale_rand));
        preempt_enable();
}

static const struct ref_scale_ops typesafe_ref_ops;
static const struct ref_scale_ops typesafe_lock_ops;
static const struct ref_scale_ops typesafe_seqlock_ops;

// Initialize for a typesafe test.
static bool typesafe_init(void)
{
        long idx;
        long si = lookup_instances;

        typesafe_kmem_cachep = kmem_cache_create("refscale_typesafe",
                                                 sizeof(struct refscale_typesafe), sizeof(void *),
                                                 SLAB_TYPESAFE_BY_RCU, refscale_typesafe_ctor);
        if (!typesafe_kmem_cachep)
                return false;
        if (si < 0)
                si = -si * nr_cpu_ids;
        else if (si == 0)
                si = nr_cpu_ids;
        rtsarray_size = si;
        rtsarray = kcalloc(si, sizeof(*rtsarray), GFP_KERNEL);
        if (!rtsarray)
                return false;
        for (idx = 0; idx < rtsarray_size; idx++) {
                rtsarray[idx] = typesafe_alloc_one();
                if (!rtsarray[idx])
                        return false;
        }
        if (cur_ops == &typesafe_ref_ops) {
                rts_acquire = typesafe_ref_acquire;
                rts_release = typesafe_ref_release;
        } else if (cur_ops == &typesafe_lock_ops) {
                rts_acquire = typesafe_lock_acquire;
                rts_release = typesafe_lock_release;
        } else if (cur_ops == &typesafe_seqlock_ops) {
                rts_acquire = typesafe_seqlock_acquire;
                rts_release = typesafe_seqlock_release;
        } else {
                WARN_ON_ONCE(1);
                return false;
        }
        return true;
}

// Clean up after a typesafe test.
static void typesafe_cleanup(void)
{
        long idx;

        if (rtsarray) {
                for (idx = 0; idx < rtsarray_size; idx++)
                        kmem_cache_free(typesafe_kmem_cachep, rtsarray[idx]);
                kfree(rtsarray);
                rtsarray = NULL;
                rtsarray_size = 0;
        }
        kmem_cache_destroy(typesafe_kmem_cachep);
        typesafe_kmem_cachep = NULL;
        rts_acquire = NULL;
        rts_release = NULL;
}

// The typesafe_init() function distinguishes these structures by address.
static const struct ref_scale_ops typesafe_ref_ops = {
        .init           = typesafe_init,
        .cleanup        = typesafe_cleanup,
        .readsection    = typesafe_read_section,
        .delaysection   = typesafe_delay_section,
        .name           = "typesafe_ref"
};

static const struct ref_scale_ops typesafe_lock_ops = {
        .init           = typesafe_init,
        .cleanup        = typesafe_cleanup,
        .readsection    = typesafe_read_section,
        .delaysection   = typesafe_delay_section,
        .name           = "typesafe_lock"
};

static const struct ref_scale_ops typesafe_seqlock_ops = {
        .init           = typesafe_init,
        .cleanup        = typesafe_cleanup,
        .readsection    = typesafe_read_section,
        .delaysection   = typesafe_delay_section,
        .name           = "typesafe_seqlock"
};

static void rcu_scale_one_reader(void)
{
        if (readdelay <= 0)
                cur_ops->readsection(loops);
        else
                cur_ops->delaysection(loops, readdelay / 1000, readdelay % 1000);
}

// Warm up cache, or, if needed run a series of rcu_scale_one_reader()
// to allow multiple rcuscale guest OSes to collect mutually valid data.
static void rcu_scale_warm_cool(void)
{
        unsigned long jdone = jiffies + (guest_os_delay > 0 ? guest_os_delay * HZ : -1);

        do {
                rcu_scale_one_reader();
                cond_resched();
        } while (time_before(jiffies, jdone));
}

// 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_BATCH("ref_scale_reader %ld: task started", me);
        WARN_ON_ONCE(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_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, raw_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(raw_smp_processor_id() != me % nr_cpu_ids);

        WRITE_ONCE(rt->start_reader, 0);
        if (!atomic_dec_return(&n_started))
                while (atomic_read_acquire(&n_started))
                        cpu_relax();

        VERBOSE_SCALEOUT_BATCH("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_BATCH("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;
        struct seq_buf s;
        char *buf;
        u64 sum = 0;

        buf = kmalloc(800 + 64, GFP_KERNEL);
        if (!buf)
                return 0;
        seq_buf_init(&s, buf, 800 + 64);

        seq_buf_printf(&s, "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]);

                if (i % 5 == 0)
                        seq_buf_putc(&s, '\n');

                if (seq_buf_used(&s) >= 800) {
                        pr_alert("%s", seq_buf_str(&s));
                        seq_buf_clear(&s);
                }

                seq_buf_printf(&s, "%d: %llu\t", i, rt->last_duration_ns);

                sum += rt->last_duration_ns;
        }
        pr_alert("%s\n", seq_buf_str(&s));

        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)
{
        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(800 + 64, GFP_KERNEL);
        if (!result_avg || !buf) {
                SCALEOUT_ERRSTRING("out of memory");
                goto oom_exit;
        }
        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
        rcu_scale_warm_cool();
        for (exp = 0; exp < nruns && !torture_must_stop(); exp++) {
                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);
        }
        rcu_scale_warm_cool();

        // Print the average of all experiments
        SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n");

        pr_alert("Runs\tTime(ns)\n");
        for (exp = 0; exp < nruns; exp++) {
                u64 avg;
                u32 rem;

                avg = div_u64_rem(result_avg[exp], 1000, &rem);
                sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
                strcat(buf, buf1);
                if (strlen(buf) >= 800) {
                        pr_alert("%s", buf);
                        buf[0] = 0;
                }
        }

        pr_alert("%s", buf);

oom_exit:
        // 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(const struct ref_scale_ops *cur_ops, const char *tag)
{
        pr_alert("%s" SCALE_FLAG
                 "--- %s:  verbose=%d verbose_batched=%d shutdown=%d holdoff=%d lookup_instances=%ld loops=%ld nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
                 verbose, verbose_batched, shutdown, holdoff, lookup_instances, 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_idle(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 const struct ref_scale_ops *scale_ops[] = {
                &rcu_ops, &srcu_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
                &refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops,
                &clock_ops, &jiffies_ops, &typesafe_ref_ops, &typesafe_lock_ops,
                &typesafe_seqlock_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");
                firsterr = -EINVAL;
                cur_ops = NULL;
                goto unwind;
        }
        if (cur_ops->init)
                if (!cur_ops->init()) {
                        firsterr = -EUCLEAN;
                        goto unwind;
                }

        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 (torture_init_error(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);
        if (WARN_ONCE(loops <= 0, "%s: loops = %ld, adjusted to 1\n", __func__, loops))
                loops = 1;
        if (WARN_ONCE(nreaders <= 0, "%s: nreaders = %d, adjusted to 1\n", __func__, nreaders))
                nreaders = 1;
        if (WARN_ONCE(nruns <= 0, "%s: nruns = %d, adjusted to 1\n", __func__, nruns))
                nruns = 1;
        reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (!reader_tasks) {
                SCALEOUT_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }

        VERBOSE_SCALEOUT("Starting %d reader threads", nreaders);

        for (i = 0; i < nreaders; i++) {
                init_waitqueue_head(&reader_tasks[i].wq);
                firsterr = torture_create_kthread(ref_scale_reader, (void *)i,
                                                  reader_tasks[i].task);
                if (torture_init_error(firsterr))
                        goto unwind;
        }

        // Main Task
        init_waitqueue_head(&main_wq);
        firsterr = torture_create_kthread(main_func, NULL, main_task);
        if (torture_init_error(firsterr))
                goto unwind;

        torture_init_end();
        return 0;

unwind:
        torture_init_end();
        ref_scale_cleanup();
        if (shutdown) {
                WARN_ON(!IS_MODULE(CONFIG_RCU_REF_SCALE_TEST));
                kernel_power_off();
        }
        return firsterr;
}

module_init(ref_scale_init);
module_exit(ref_scale_cleanup);