/* * 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_slowpath	- # of locking operations via the slowpath *   pv_lock_stealing	- # of lock stealing operations *   pv_spurious_wakeup	- # of spurious wakeups in non-head vCPUs *   pv_wait_again	- # of wait's after a queue head 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_slowpath,	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/sched/clock.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_slowpath]   = "pv_lock_slowpath",	[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	 */	counter = (long)file_inode(file)->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 = 0; 		if (kicks) {			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)) {			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 ((long)file_inode(file)->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);	}	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)		goto out; 	/*	 * 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++)		if (!debugfs_create_file(qstat_names[i], 0400, d_qstat,					 (void *)(long)i, &fops_qstat))			goto fail_undo; 	if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,				 (void *)(long)qstat_reset_cnts, &fops_qstat))		goto fail_undo; 	return 0;fail_undo:	debugfs_remove_recursive(d_qstat);out:	pr_warn("Could not create 'qlockstat' debugfs entries\n");	return -ENOMEM;}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) #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 */