Function devstat_end_transaction

freebsd/kern/subr_devstat.c:300–344

* Record the ending of a transaction, and incrment the various counters. * * Ordering in this function, and in devstat_start_transaction() is VERY * important. The idea here is to run without locks, so we are very * careful to only modify some fields on the way "down" (i.e. at * transaction start) and some fields on the way "up" (i.e. at transaction * completion). One exception is busy_fro

 * atomic instructions using appropriate memory barriers.
 */
void
devstat_end_transaction(struct devstat *ds, uint32_t bytes, 
			devstat_tag_type tag_type, devstat_trans_flags flags,
			const struct bintime *now, const struct bintime *then)
{
	struct bintime dt, lnow;

	/* sanity check */
	if (ds == NULL)
		return;

	if (now == NULL) {
		binuptime(&lnow);
		now = &lnow;
	}

	atomic_add_acq_int(&ds->sequence1, 1);
	/* Update byte and operations counts */
	ds->bytes[flags] += bytes;
	ds->operations[flags]++;

	/*
	 * Keep a count of the various tag types sent.
	 */
	if ((ds->flags & DEVSTAT_NO_ORDERED_TAGS) == 0 &&
	    tag_type != DEVSTAT_TAG_NONE)
		ds->tag_types[tag_type]++;

	if (then != NULL) {
		/* Update duration of operations */
		dt = *now;
		bintime_sub(&dt, then);
		bintime_add(&ds->duration[flags], &dt);
	}

	/* Accumulate busy time */
	dt = *now;
	bintime_sub(&dt, &ds->busy_from);
	bintime_add(&ds->busy_time, &dt);
	ds->busy_from = *now;

	ds->end_count++;
	atomic_add_rel_int(&ds->sequence0, 1);
	DTRACE_DEVSTAT_DONE();
}

void
devstat_end_transaction_bio(struct devstat *ds, const struct bio *bp)