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rmd256.c

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  • latencytop.c 7.88 KiB
    /*
     * latencytop.c: Latency display infrastructure
     *
     * (C) Copyright 2008 Intel Corporation
     * Author: Arjan van de Ven <arjan@linux.intel.com>
     *
     * 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; version 2
     * of the License.
     */
    
    /*
     * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
     * used by the "latencytop" userspace tool. The latency that is tracked is not
     * the 'traditional' interrupt latency (which is primarily caused by something
     * else consuming CPU), but instead, it is the latency an application encounters
     * because the kernel sleeps on its behalf for various reasons.
     *
     * This code tracks 2 levels of statistics:
     * 1) System level latency
     * 2) Per process latency
     *
     * The latency is stored in fixed sized data structures in an accumulated form;
     * if the "same" latency cause is hit twice, this will be tracked as one entry
     * in the data structure. Both the count, total accumulated latency and maximum
     * latency are tracked in this data structure. When the fixed size structure is
     * full, no new causes are tracked until the buffer is flushed by writing to
     * the /proc file; the userspace tool does this on a regular basis.
     *
     * A latency cause is identified by a stringified backtrace at the point that
     * the scheduler gets invoked. The userland tool will use this string to
     * identify the cause of the latency in human readable form.
     *
     * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
     * These files look like this:
     *
     * Latency Top version : v0.1
     * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
     * |    |    |    |
     * |    |    |    +----> the stringified backtrace
     * |    |    +---------> The maximum latency for this entry in microseconds
     * |    +--------------> The accumulated latency for this entry (microseconds)
     * +-------------------> The number of times this entry is hit
     *
     * (note: the average latency is the accumulated latency divided by the number
     * of times)
     */
    
    #include <linux/kallsyms.h>
    #include <linux/seq_file.h>
    #include <linux/notifier.h>
    #include <linux/spinlock.h>
    #include <linux/proc_fs.h>
    #include <linux/latencytop.h>
    #include <linux/export.h>
    #include <linux/sched.h>
    #include <linux/sched/debug.h>
    #include <linux/sched/stat.h>
    #include <linux/list.h>
    #include <linux/stacktrace.h>
    
    static DEFINE_RAW_SPINLOCK(latency_lock);
    
    #define MAXLR 128
    static struct latency_record latency_record[MAXLR];
    
    int latencytop_enabled;
    
    void clear_all_latency_tracing(struct task_struct *p)
    {
    	unsigned long flags;
    
    	if (!latencytop_enabled)
    		return;
    
    	raw_spin_lock_irqsave(&latency_lock, flags);
    	memset(&p->latency_record, 0, sizeof(p->latency_record));
    	p->latency_record_count = 0;
    	raw_spin_unlock_irqrestore(&latency_lock, flags);
    }
    
    static void clear_global_latency_tracing(void)
    {
    	unsigned long flags;
    
    	raw_spin_lock_irqsave(&latency_lock, flags);
    	memset(&latency_record, 0, sizeof(latency_record));
    	raw_spin_unlock_irqrestore(&latency_lock, flags);
    }
    
    static void __sched
    account_global_scheduler_latency(struct task_struct *tsk,
    				 struct latency_record *lat)
    {
    	int firstnonnull = MAXLR + 1;
    	int i;
    
    	if (!latencytop_enabled)
    		return;
    
    	/* skip kernel threads for now */
    	if (!tsk->mm)
    		return;
    
    	for (i = 0; i < MAXLR; i++) {
    		int q, same = 1;
    
    		/* Nothing stored: */
    		if (!latency_record[i].backtrace[0]) {
    			if (firstnonnull > i)
    				firstnonnull = i;
    			continue;
    		}
    		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
    			unsigned long record = lat->backtrace[q];
    
    			if (latency_record[i].backtrace[q] != record) {
    				same = 0;
    				break;
    			}
    
    			/* 0 and ULONG_MAX entries mean end of backtrace: */
    			if (record == 0 || record == ULONG_MAX)
    				break;
    		}
    		if (same) {
    			latency_record[i].count++;
    			latency_record[i].time += lat->time;
    			if (lat->time > latency_record[i].max)
    				latency_record[i].max = lat->time;
    			return;
    		}
    	}
    
    	i = firstnonnull;
    	if (i >= MAXLR - 1)
    		return;
    
    	/* Allocted a new one: */
    	memcpy(&latency_record[i], lat, sizeof(struct latency_record));
    }
    
    /*
     * Iterator to store a backtrace into a latency record entry
     */
    static inline void store_stacktrace(struct task_struct *tsk,
    					struct latency_record *lat)
    {
    	struct stack_trace trace;
    
    	memset(&trace, 0, sizeof(trace));
    	trace.max_entries = LT_BACKTRACEDEPTH;
    	trace.entries = &lat->backtrace[0];
    	save_stack_trace_tsk(tsk, &trace);
    }
    
    /**
     * __account_scheduler_latency - record an occurred latency
     * @tsk - the task struct of the task hitting the latency
     * @usecs - the duration of the latency in microseconds
     * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
     *
     * This function is the main entry point for recording latency entries
     * as called by the scheduler.
     *
     * This function has a few special cases to deal with normal 'non-latency'
     * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
     * since this usually is caused by waiting for events via select() and co.
     *
     * Negative latencies (caused by time going backwards) are also explicitly
     * skipped.
     */
    void __sched
    __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
    {
    	unsigned long flags;
    	int i, q;
    	struct latency_record lat;
    
    	/* Long interruptible waits are generally user requested... */
    	if (inter && usecs > 5000)
    		return;
    
    	/* Negative sleeps are time going backwards */
    	/* Zero-time sleeps are non-interesting */
    	if (usecs <= 0)
    		return;
    
    	memset(&lat, 0, sizeof(lat));
    	lat.count = 1;
    	lat.time = usecs;
    	lat.max = usecs;
    	store_stacktrace(tsk, &lat);
    
    	raw_spin_lock_irqsave(&latency_lock, flags);
    
    	account_global_scheduler_latency(tsk, &lat);
    
    	for (i = 0; i < tsk->latency_record_count; i++) {
    		struct latency_record *mylat;
    		int same = 1;
    
    		mylat = &tsk->latency_record[i];
    		for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
    			unsigned long record = lat.backtrace[q];
    
    			if (mylat->backtrace[q] != record) {
    				same = 0;
    				break;
    			}
    
    			/* 0 and ULONG_MAX entries mean end of backtrace: */
    			if (record == 0 || record == ULONG_MAX)
    				break;
    		}
    		if (same) {
    			mylat->count++;
    			mylat->time += lat.time;
    			if (lat.time > mylat->max)
    				mylat->max = lat.time;
    			goto out_unlock;
    		}
    	}
    
    	/*
    	 * short term hack; if we're > 32 we stop; future we recycle:
    	 */
    	if (tsk->latency_record_count >= LT_SAVECOUNT)
    		goto out_unlock;
    
    	/* Allocated a new one: */
    	i = tsk->latency_record_count++;
    	memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
    
    out_unlock:
    	raw_spin_unlock_irqrestore(&latency_lock, flags);
    }
    
    static int lstats_show(struct seq_file *m, void *v)
    {
    	int i;
    
    	seq_puts(m, "Latency Top version : v0.1\n");
    
    	for (i = 0; i < MAXLR; i++) {
    		struct latency_record *lr = &latency_record[i];
    
    		if (lr->backtrace[0]) {
    			int q;
    			seq_printf(m, "%i %lu %lu",
    				   lr->count, lr->time, lr->max);
    			for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
    				unsigned long bt = lr->backtrace[q];
    				if (!bt)
    					break;
    				if (bt == ULONG_MAX)
    					break;
    				seq_printf(m, " %ps", (void *)bt);
    			}
    			seq_puts(m, "\n");
    		}
    	}
    	return 0;
    }
    
    static ssize_t
    lstats_write(struct file *file, const char __user *buf, size_t count,
    	     loff_t *offs)
    {
    	clear_global_latency_tracing();
    
    	return count;
    }
    
    static int lstats_open(struct inode *inode, struct file *filp)
    {
    	return single_open(filp, lstats_show, NULL);
    }
    
    static const struct file_operations lstats_fops = {
    	.open		= lstats_open,
    	.read		= seq_read,
    	.write		= lstats_write,
    	.llseek		= seq_lseek,
    	.release	= single_release,
    };
    
    static int __init init_lstats_procfs(void)
    {
    	proc_create("latency_stats", 0644, NULL, &lstats_fops);
    	return 0;
    }
    
    int sysctl_latencytop(struct ctl_table *table, int write,
    			void __user *buffer, size_t *lenp, loff_t *ppos)
    {
    	int err;
    
    	err = proc_dointvec(table, write, buffer, lenp, ppos);
    	if (latencytop_enabled)
    		force_schedstat_enabled();
    
    	return err;
    }
    device_initcall(init_lstats_procfs);