path: root/fs/gfs2/lock_dlm.c

/*
 * Copyright (C) Sistina Software, Inc.  1997-2003 All rights reserved.
 * Copyright 2004-2011 Red Hat, Inc.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU General Public License version 2.
 */

#include <linux/fs.h>
#include <linux/dlm.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/delay.h>
#include <linux/gfs2_ondisk.h>

#include "incore.h"
#include "glock.h"
#include "util.h"
#include "sys.h"
#include "trace_gfs2.h"

extern struct workqueue_struct *gfs2_control_wq;

/**
 * gfs2_update_stats - Update time based stats
 * @mv: Pointer to mean/variance structure to update
 * @sample: New data to include
 *
 * @delta is the difference between the current rtt sample and the
 * running average srtt. We add 1/8 of that to the srtt in order to
 * update the current srtt estimate. The varience estimate is a bit
 * more complicated. We subtract the abs value of the @delta from
 * the current variance estimate and add 1/4 of that to the running
 * total.
 *
 * Note that the index points at the array entry containing the smoothed
 * mean value, and the variance is always in the following entry
 *
 * Reference: TCP/IP Illustrated, vol 2, p. 831,832
 * All times are in units of integer nanoseconds. Unlike the TCP/IP case,
 * they are not scaled fixed point.
 */

static inline void gfs2_update_stats(struct gfs2_lkstats *s, unsigned index,
				     s64 sample)
{
	s64 delta = sample - s->stats[index];
	s->stats[index] += (delta >> 3);
	index++;
	s->stats[index] += ((abs64(delta) - s->stats[index]) >> 2);
}

/**
 * gfs2_update_reply_times - Update locking statistics
 * @gl: The glock to update
 *
 * This assumes that gl->gl_dstamp has been set earlier.
 *
 * The rtt (lock round trip time) is an estimate of the time
 * taken to perform a dlm lock request. We update it on each
 * reply from the dlm.
 *
 * The blocking flag is set on the glock for all dlm requests
 * which may potentially block due to lock requests from other nodes.
 * DLM requests where the current lock state is exclusive, the
 * requested state is null (or unlocked) or where the TRY or
 * TRY_1CB flags are set are classified as non-blocking. All
 * other DLM requests are counted as (potentially) blocking.
 */
static inline void gfs2_update_reply_times(struct gfs2_glock *gl)
{
	struct gfs2_pcpu_lkstats *lks;
	const unsigned gltype = gl->gl_name.ln_type;
	unsigned index = test_bit(GLF_BLOCKING, &gl->gl_flags) ?
			 GFS2_LKS_SRTTB : GFS2_LKS_SRTT;
	s64 rtt;

	preempt_disable();
	rtt = ktime_to_ns(ktime_sub(ktime_get_real(), gl->gl_dstamp));
	lks = this_cpu_ptr(gl->gl_sbd->sd_lkstats);
	gfs2_update_stats(&gl->gl_stats, index, rtt);		/* Local */
	gfs2_update_stats(&lks->lkstats[gltype], index, rtt);	/* Global */
	preempt_enable();

	trace_gfs2_glock_lock_time(gl, rtt);
}

/**
 * gfs2_update_request_times - Update locking statistics
 * @gl: The glock to update
 *
 * The irt (lock inter-request times) measures the average time