+/*
+ * test-read-lock-speed.c
+ *
+ * Compare speed of :
+ * - spin lock irqsave / spin unlock irqrestore (close to rwlocks when
+ * uncontended)
+ * - using a sequence read lock (uncontended)
+ * - preempt disable/enable (RCU)
+ *
+ * Copyright 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Distributed under GPLv2
+ */
+
+#include <linux/jiffies.h>
+#include <linux/compiler.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/math64.h>
+#include <linux/spinlock.h>
+#include <linux/seqlock.h>
+#include <linux/cpumask.h>
+#include <asm/timex.h>
+#include <asm/system.h>
+
+#define NR_LOOPS 20000
+
+#ifndef CONFIG_PREEMPT
+#error "Your kernel should be build with preemption enabled"
+#endif
+
+#ifdef CONFIG_DEBUG_PREEMPT
+#error "Please disable CONFIG_DEBUG_PREEMPT"
+#endif
+
+#ifdef CONFIG_DEBUG_SPINLOCK
+#error "Please disable CONFIG_DEBUG_SPINLOCK"
+#endif
+
+#ifdef CONFIG_LOCKDEP
+#error "Please disable CONFIG_LOCKDEP"
+#endif
+
+int test_val;
+
+static void do_testbaseline(void)
+{
+ unsigned long flags;
+ unsigned int i;
+ cycles_t time1, time2, time;
+ u32 rem;
+
+ local_irq_save(flags);
+ preempt_disable();
+ time1 = get_cycles();
+ for (i = 0; i < NR_LOOPS; i++) {
+ asm volatile ("");
+ }
+ time2 = get_cycles();
+ local_irq_restore(flags);
+ preempt_enable();
+ time = time2 - time1;
+
+ printk(KERN_ALERT "test results: time for baseline\n");
+ printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
+ printk(KERN_ALERT "total time: %llu\n", time);
+ time = div_u64_rem(time, NR_LOOPS, &rem);
+ printk(KERN_ALERT "-> baseline takes %llu cycles\n", time);
+ printk(KERN_ALERT "test end\n");
+}
+
+static void do_test_spinlock(void)
+{
+ static DEFINE_SPINLOCK(mylock);
+ unsigned long flags;
+ unsigned int i;
+ cycles_t time1, time2, time;
+ u32 rem;
+
+ preempt_disable();
+ spin_lock_irqsave(&mylock, flags);
+ time1 = get_cycles();
+ for (i = 0; i < NR_LOOPS; i++) {
+ spin_unlock(&mylock);
+ spin_lock(&mylock);
+ }
+ time2 = get_cycles();
+ spin_unlock_irqrestore(&mylock, flags);
+ preempt_enable();
+ time = time2 - time1;
+
+ printk(KERN_ALERT "test results: time for spinlock\n");
+ printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
+ printk(KERN_ALERT "total time: %llu\n", time);
+ time = div_u64_rem(time, NR_LOOPS, &rem);
+ printk(KERN_ALERT "-> spinlock takes %llu cycles\n", time);
+ printk(KERN_ALERT "test end\n");
+}
+
+static void do_test_seqlock(void)
+{
+ static seqlock_t test_lock;
+ unsigned long seq;
+ unsigned long flags;
+ unsigned int i;
+ cycles_t time1, time2, time;
+ u32 rem;
+
+ local_irq_save(flags);
+ time1 = get_cycles();
+ for (i = 0; i < NR_LOOPS; i++) {
+ do {
+ seq = read_seqbegin(&test_lock);
+ } while (read_seqretry(&test_lock, seq));
+ }
+ time2 = get_cycles();
+ time = time2 - time1;
+ local_irq_restore(flags);
+
+ printk(KERN_ALERT "test results: time for seqlock\n");
+ printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
+ printk(KERN_ALERT "total time: %llu\n", time);
+ time = div_u64_rem(time, NR_LOOPS, &rem);
+ printk(KERN_ALERT "-> seqlock takes %llu cycles\n", time);
+ printk(KERN_ALERT "test end\n");
+}
+
+/*
+ * Note : This test _should_ trigger lockdep errors due to preemption
+ * disabling/enabling within irq off section. Given we are only interested in
+ * having the most precise measurement for preemption disable/enable, we don't
+ * care about this.
+ */
+static void do_test_preempt(void)
+{
+ unsigned long flags;
+ unsigned int i;
+ cycles_t time1, time2, time;
+ u32 rem;
+
+ local_irq_save(flags);
+ preempt_disable();
+ time1 = get_cycles();
+ for (i = 0; i < NR_LOOPS; i++) {
+ preempt_disable();
+ preempt_enable();
+ }
+ time2 = get_cycles();
+ preempt_enable();
+ time = time2 - time1;
+ local_irq_restore(flags);
+
+ printk(KERN_ALERT
+ "test results: time for preempt disable/enable pairs\n");
+ printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
+ printk(KERN_ALERT "total time: %llu\n", time);
+ time = div_u64_rem(time, NR_LOOPS, &rem);
+ printk(KERN_ALERT "-> preempt disable/enable pair takes %llu cycles\n",
+ time);
+ printk(KERN_ALERT "test end\n");
+}
+
+static int ltt_test_init(void)
+{
+ printk(KERN_ALERT "test init\n");
+
+ printk(KERN_ALERT "Number of active CPUs : %d\n", num_online_cpus());
+ do_testbaseline();
+ do_test_spinlock();
+ do_test_seqlock();
+ do_test_preempt();
+ return -EAGAIN; /* Fail will directly unload the module */
+}
+
+static void ltt_test_exit(void)
+{
+ printk(KERN_ALERT "test exit\n");
+}
+
+module_init(ltt_test_init)
+module_exit(ltt_test_exit)
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("Test read lock speed");