1 files changed, 300 insertions, 0 deletions

diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
new file mode 100644
index 000000000000..640dcecdd1df
--- /dev/null
+++ b/kernel/locking/qspinlock_stat.h
@@ -0,0 +1,300 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Authors: Waiman Long <waiman.long@hpe.com>
+ */
+
+/*
+ * When queued spinlock statistical counters are enabled, the following
+ * debugfs files will be created for reporting the counter values:
+ *
+ * <debugfs>/qlockstat/
+ *   pv_hash_hops       - average # of hops per hashing operation
+ *   pv_kick_unlock     - # of vCPU kicks issued at unlock time
+ *   pv_kick_wake       - # of vCPU kicks used for computing pv_latency_wake
+ *   pv_latency_kick    - average latency (ns) of vCPU kick operation
+ *   pv_latency_wake    - average latency (ns) from vCPU kick to wakeup
+ *   pv_lock_stealing   - # of lock stealing operations
+ *   pv_spurious_wakeup - # of spurious wakeups
+ *   pv_wait_again      - # of vCPU wait's that happened after a vCPU kick
+ *   pv_wait_early      - # of early vCPU wait's
+ *   pv_wait_head       - # of vCPU wait's at the queue head
+ *   pv_wait_node       - # of vCPU wait's at a non-head queue node
+ *
+ * Writing to the "reset_counters" file will reset all the above counter
+ * values.
+ *
+ * These statistical counters are implemented as per-cpu variables which are
+ * summed and computed whenever the corresponding debugfs files are read. This
+ * minimizes added overhead making the counters usable even in a production
+ * environment.
+ *
+ * There may be slight difference between pv_kick_wake and pv_kick_unlock.
+ */
+enum qlock_stats {
+        qstat_pv_hash_hops,
+        qstat_pv_kick_unlock,
+        qstat_pv_kick_wake,
+        qstat_pv_latency_kick,
+        qstat_pv_latency_wake,
+        qstat_pv_lock_stealing,
+        qstat_pv_spurious_wakeup,
+        qstat_pv_wait_again,
+        qstat_pv_wait_early,
+        qstat_pv_wait_head,
+        qstat_pv_wait_node,
+        qstat_num,      /* Total number of statistical counters */
+        qstat_reset_cnts = qstat_num,
+};
+
+#ifdef CONFIG_QUEUED_LOCK_STAT
+/*
+ * Collect pvqspinlock statistics
+ */
+#include <linux/debugfs.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+
+static const char * const qstat_names[qstat_num + 1] = {
+        [qstat_pv_hash_hops]       = "pv_hash_hops",
+        [qstat_pv_kick_unlock]     = "pv_kick_unlock",
+        [qstat_pv_kick_wake]       = "pv_kick_wake",
+        [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup",
+        [qstat_pv_latency_kick]    = "pv_latency_kick",
+        [qstat_pv_latency_wake]    = "pv_latency_wake",
+        [qstat_pv_lock_stealing]   = "pv_lock_stealing",
+        [qstat_pv_wait_again]      = "pv_wait_again",
+        [qstat_pv_wait_early]      = "pv_wait_early",
+        [qstat_pv_wait_head]       = "pv_wait_head",
+        [qstat_pv_wait_node]       = "pv_wait_node",
+        [qstat_reset_cnts]         = "reset_counters",
+};
+
+/*
+ * Per-cpu counters
+ */
+static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]);
+static DEFINE_PER_CPU(u64, pv_kick_time);
+
+/*
+ * Function to read and return the qlock statistical counter values
+ *
+ * The following counters are handled specially:
+ * 1. qstat_pv_latency_kick
+ *    Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
+ * 2. qstat_pv_latency_wake
+ *    Average wake latency (ns) = pv_latency_wake/pv_kick_wake
+ * 3. qstat_pv_hash_hops
+ *    Average hops/hash = pv_hash_hops/pv_kick_unlock
+ */
+static ssize_t qstat_read(struct file *file, char __user *user_buf,
+                          size_t count, loff_t *ppos)
+{
+        char buf[64];
+        int cpu, counter, len;
+        u64 stat = 0, kicks = 0;
+
+        /*
+         * Get the counter ID stored in file->f_inode->i_private
+         */
+        if (!file->f_inode) {
+                WARN_ON_ONCE(1);
+                return -EBADF;
+        }
+        counter = (long)(file->f_inode->i_private);
+
+        if (counter >= qstat_num)
+                return -EBADF;
+
+        for_each_possible_cpu(cpu) {
+                stat += per_cpu(qstats[counter], cpu);
+                /*
+                 * Need to sum additional counter for some of them
+                 */
+                switch (counter) {
+
+                case qstat_pv_latency_kick:
+                case qstat_pv_hash_hops:
+                        kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
+                        break;
+
+                case qstat_pv_latency_wake:
+                        kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
+                        break;
+                }
+        }
+
+        if (counter == qstat_pv_hash_hops) {
+                u64 frac;
+
+                frac = 100ULL * do_div(stat, kicks);
+                frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
+
+                /*
+                 * Return a X.XX decimal number
+                 */
+                len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac);
+        } else {
+                /*
+                 * Round to the nearest ns
+                 */
+                if ((counter == qstat_pv_latency_kick) ||
+                    (counter == qstat_pv_latency_wake)) {
+                        stat = 0;
+                        if (kicks)
+                                stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
+                }
+                len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
+        }
+
+        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+
+/*
+ * Function to handle write request
+ *
+ * When counter = reset_cnts, reset all the counter values.
+ * Since the counter updates aren't atomic, the resetting is done twice
+ * to make sure that the counters are very likely to be all cleared.
+ */
+static ssize_t qstat_write(struct file *file, const char __user *user_buf,
+                           size_t count, loff_t *ppos)
+{
+        int cpu;
+
+        /*
+         * Get the counter ID stored in file->f_inode->i_private
+         */
+        if (!file->f_inode) {
+                WARN_ON_ONCE(1);
+                return -EBADF;
+        }
+        if ((long)(file->f_inode->i_private) != qstat_reset_cnts)
+                return count;
+
+        for_each_possible_cpu(cpu) {
+                int i;
+                unsigned long *ptr = per_cpu_ptr(qstats, cpu);
+
+                for (i = 0 ; i < qstat_num; i++)
+                        WRITE_ONCE(ptr[i], 0);
+                for (i = 0 ; i < qstat_num; i++)
+                        WRITE_ONCE(ptr[i], 0);
+        }
+        return count;
+}
+
+/*
+ * Debugfs data structures
+ */
+static const struct file_operations fops_qstat = {
+        .read = qstat_read,
+        .write = qstat_write,
+        .llseek = default_llseek,
+};
+
+/*
+ * Initialize debugfs for the qspinlock statistical counters
+ */
+static int __init init_qspinlock_stat(void)
+{
+        struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
+        int i;
+
+        if (!d_qstat) {
+                pr_warn("Could not create 'qlockstat' debugfs directory\n");
+                return 0;
+        }
+
+        /*
+         * Create the debugfs files
+         *
+         * As reading from and writing to the stat files can be slow, only
+         * root is allowed to do the read/write to limit impact to system
+         * performance.
+         */
+        for (i = 0; i < qstat_num; i++)
+                debugfs_create_file(qstat_names[i], 0400, d_qstat,
+                                   (void *)(long)i, &fops_qstat);
+
+        debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
+                           (void *)(long)qstat_reset_cnts, &fops_qstat);
+        return 0;
+}
+fs_initcall(init_qspinlock_stat);
+
+/*
+ * Increment the PV qspinlock statistical counters
+ */
+static inline void qstat_inc(enum qlock_stats stat, bool cond)
+{
+        if (cond)
+                this_cpu_inc(qstats[stat]);
+}
+
+/*
+ * PV hash hop count
+ */
+static inline void qstat_hop(int hopcnt)
+{
+        this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt);
+}
+
+/*
+ * Replacement function for pv_kick()
+ */
+static inline void __pv_kick(int cpu)
+{
+        u64 start = sched_clock();
+
+        per_cpu(pv_kick_time, cpu) = start;
+        pv_kick(cpu);
+        this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start);
+}
+
+/*
+ * Replacement function for pv_wait()
+ */
+static inline void __pv_wait(u8 *ptr, u8 val)
+{
+        u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
+
+        *pkick_time = 0;
+        pv_wait(ptr, val);
+        if (*pkick_time) {
+                this_cpu_add(qstats[qstat_pv_latency_wake],
+                             sched_clock() - *pkick_time);
+                qstat_inc(qstat_pv_kick_wake, true);
+        }
+}
+
+#define pv_kick(c)      __pv_kick(c)
+#define pv_wait(p, v)   __pv_wait(p, v)
+
+/*
+ * PV unfair trylock count tracking function
+ */
+static inline int qstat_spin_steal_lock(struct qspinlock *lock)
+{
+        int ret = pv_queued_spin_steal_lock(lock);
+
+        qstat_inc(qstat_pv_lock_stealing, ret);
+        return ret;
+}
+#undef  queued_spin_trylock
+#define queued_spin_trylock(l)  qstat_spin_steal_lock(l)
+
+#else /* CONFIG_QUEUED_LOCK_STAT */
+
+static inline void qstat_inc(enum qlock_stats stat, bool cond)  { }
+static inline void qstat_hop(int hopcnt)                        { }
+
+#endif /* CONFIG_QUEUED_LOCK_STAT */