xref: /src/sys/kern/bufq_priocscan.c

/*	$NetBSD: bufq_priocscan.c,v 1.15 2011/11/02 15:14:49 yamt Exp $	*/

/*-
 * Copyright (c)2004,2005,2006,2008,2009 YAMAMOTO Takashi,
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: bufq_priocscan.c,v 1.15 2011/11/02 15:14:49 yamt Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/bufq.h>
#include <sys/bufq_impl.h>
#include <sys/kmem.h>

/*
 * Cyclical scan (CSCAN)
 */
TAILQ_HEAD(bqhead, buf);
struct cscan_queue {
	struct bqhead cq_head[2];	/* actual lists of buffers */
	unsigned int cq_idx;		/* current list index */
	int cq_lastcylinder;		/* b_cylinder of the last request */
	daddr_t cq_lastrawblkno;	/* b_rawblkno of the last request */
};

static inline int cscan_empty(const struct cscan_queue *);
static void cscan_put(struct cscan_queue *, struct buf *, int);
static struct buf *cscan_get(struct cscan_queue *, int);
static void cscan_init(struct cscan_queue *);

static inline int
cscan_empty(const struct cscan_queue *q)
{

	return TAILQ_EMPTY(&q->cq_head[0]) && TAILQ_EMPTY(&q->cq_head[1]);
}

static void
cscan_put(struct cscan_queue *q, struct buf *bp, int sortby)
{
	struct buf tmp;
	struct buf *it;
	struct bqhead *bqh;
	unsigned int idx;

	tmp.b_cylinder = q->cq_lastcylinder;
	tmp.b_rawblkno = q->cq_lastrawblkno;

	if (buf_inorder(bp, &tmp, sortby))
		idx = 1 - q->cq_idx;
	else
		idx = q->cq_idx;

	bqh = &q->cq_head[idx];

	TAILQ_FOREACH(it, bqh, b_actq)
		if (buf_inorder(bp, it, sortby))
			break;

	if (it != NULL)
		TAILQ_INSERT_BEFORE(it, bp, b_actq);
	else
		TAILQ_INSERT_TAIL(bqh, bp, b_actq);
}

static struct buf *
cscan_get(struct cscan_queue *q, int remove)
{
	unsigned int idx = q->cq_idx;
	struct bqhead *bqh;
	struct buf *bp;

	bqh = &q->cq_head[idx];
	bp = TAILQ_FIRST(bqh);

	if (bp == NULL) {
		/* switch queue */
		idx = 1 - idx;
		bqh = &q->cq_head[idx];
		bp = TAILQ_FIRST(bqh);
	}

	KDASSERT((bp != NULL && !cscan_empty(q)) ||
	         (bp == NULL && cscan_empty(q)));

	if (bp != NULL && remove) {
		q->cq_idx = idx;
		TAILQ_REMOVE(bqh, bp, b_actq);

		q->cq_lastcylinder = bp->b_cylinder;
		q->cq_lastrawblkno =
		    bp->b_rawblkno + (bp->b_bcount >> DEV_BSHIFT);
	}

	return (bp);
}

static void
cscan_init(struct cscan_queue *q)
{

	TAILQ_INIT(&q->cq_head[0]);
	TAILQ_INIT(&q->cq_head[1]);
}


/*
 * Per-prioritiy CSCAN.
 *
 * XXX probably we should have a way to raise
 * priority of the on-queue requests.
 */
#define	PRIOCSCAN_NQUEUE	3

struct priocscan_queue {
	struct cscan_queue q_queue;
	unsigned int q_burst;
};

struct bufq_priocscan {
	struct priocscan_queue bq_queue[PRIOCSCAN_NQUEUE];

#if 0
	/*
	 * XXX using "global" head position can reduce positioning time
	 * when switching between queues.
	 * although it might affect against fairness.
	 */
	daddr_t bq_lastrawblkno;
	int bq_lastcylinder;
#endif
};

/*
 * how many requests to serve when having pending requests on other queues.
 *
 * XXX tune
 * be careful: while making these values larger likely
 * increases the total throughput, it can also increase latencies
 * for some workloads.
 */
const int priocscan_burst[] = {
	64, 16, 4
};

static void bufq_priocscan_init(struct bufq_state *);
static void bufq_priocscan_put(struct bufq_state *, struct buf *);
static struct buf *bufq_priocscan_get(struct bufq_state *, int);

BUFQ_DEFINE(priocscan, 40, bufq_priocscan_init);

static inline struct cscan_queue *bufq_priocscan_selectqueue(
    struct bufq_priocscan *, const struct buf *);

static inline struct cscan_queue *
bufq_priocscan_selectqueue(struct bufq_priocscan *q, const struct buf *bp)
{
	static const int priocscan_priomap[] = {
		[BPRIO_TIMENONCRITICAL] = 2,
		[BPRIO_TIMELIMITED] = 1,
		[BPRIO_TIMECRITICAL] = 0
	};

	return &q->bq_queue[priocscan_priomap[BIO_GETPRIO(bp)]].q_queue;
}

static void
bufq_priocscan_put(struct bufq_state *bufq, struct buf *bp)
{
	struct bufq_priocscan *q = bufq->bq_private;
	struct cscan_queue *cq;
	const int sortby = bufq->bq_flags & BUFQ_SORT_MASK;

	cq = bufq_priocscan_selectqueue(q, bp);
	cscan_put(cq, bp, sortby);
}

static struct buf *
bufq_priocscan_get(struct bufq_state *bufq, int remove)
{
	struct bufq_priocscan *q = bufq->bq_private;
	struct priocscan_queue *pq, *npq;
	struct priocscan_queue *first; /* highest priority non-empty queue */
	const struct priocscan_queue *epq;
	struct buf *bp;
	bool single; /* true if there's only one non-empty queue */

	/*
	 * find the highest priority non-empty queue.
	 */
	pq = &q->bq_queue[0];
	epq = pq + PRIOCSCAN_NQUEUE;
	for (; pq < epq; pq++) {
		if (!cscan_empty(&pq->q_queue)) {
			break;
		}
	}
	if (pq == epq) {
		/*
		 * all our queues are empty.  there's nothing to serve.
		 */
		return NULL;
	}
	first = pq;

	/*
	 * scan the rest of queues.
	 *
	 * if we have two or more non-empty queues, we serve the highest
	 * priority one with non-zero burst count.
	 */
	single = true;
	for (npq = pq + 1; npq < epq; npq++) {
		if (!cscan_empty(&npq->q_queue)) {
			/*
			 * we found another non-empty queue.
			 * it means that a queue needs to consume its burst
			 * count to be served.
			 */
			single = false;

			/*
			 * check if our current candidate queue has already
			 * exhausted its burst count.
			 */
			if (pq->q_burst > 0) {
				break;
			}
			pq = npq;
		}
	}
	if (single) {
		/*
		 * there's only a non-empty queue.
		 * just serve it without consuming its burst count.
		 */
		KASSERT(pq == first);
	} else {
		/*
		 * there are two or more non-empty queues.
		 */
		if (pq->q_burst == 0) {
			/*
			 * no queues can be served because they have already
			 * exhausted their burst count.
			 */
			unsigned int i;
#ifdef DEBUG
			for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
				pq = &q->bq_queue[i];
				if (!cscan_empty(&pq->q_queue) && pq->q_burst) {
					panic("%s: inconsist", __func__);
				}
			}
#endif /* DEBUG */
			/*
			 * reset burst counts.
			 */
			if (remove) {
				for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
					pq = &q->bq_queue[i];
					pq->q_burst = priocscan_burst[i];
				}
			}

			/*
			 * serve the highest priority non-empty queue.
			 */
			pq = first;
		}
		/*
		 * consume the burst count.
		 *
		 * XXX account only by number of requests.  is it good enough?
		 */
		KASSERT(pq->q_burst > 0);
		if (remove) {
			pq->q_burst--;
		}
	}

	/*
	 * finally, get a request from the selected queue.
	 */
	KDASSERT(!cscan_empty(&pq->q_queue));
	bp = cscan_get(&pq->q_queue, remove);
	KDASSERT(bp != NULL);
	KDASSERT(&pq->q_queue == bufq_priocscan_selectqueue(q, bp));

	return bp;
}

static struct buf *
bufq_priocscan_cancel(struct bufq_state *bufq, struct buf *bp)
{
	struct bufq_priocscan * const q = bufq->bq_private;
	unsigned int i, j;

	for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
		struct cscan_queue * const cq = &q->bq_queue[i].q_queue;
		for (j = 0; j < 2; j++) {
			struct bqhead * const bqh = &cq->cq_head[j];
			struct buf *bq;

			TAILQ_FOREACH(bq, bqh, b_actq) {
				if (bq == bp) {
					TAILQ_REMOVE(bqh, bp, b_actq);
					return bp;
				}
			}
		}
	}
	return NULL;
}

static void
bufq_priocscan_fini(struct bufq_state *bufq)
{

	KASSERT(bufq->bq_private != NULL);
	kmem_free(bufq->bq_private, sizeof(struct bufq_priocscan));
}

static void
bufq_priocscan_init(struct bufq_state *bufq)
{
	struct bufq_priocscan *q;
	unsigned int i;

	bufq->bq_get = bufq_priocscan_get;
	bufq->bq_put = bufq_priocscan_put;
	bufq->bq_cancel = bufq_priocscan_cancel;
	bufq->bq_fini = bufq_priocscan_fini;
	bufq->bq_private = kmem_zalloc(sizeof(struct bufq_priocscan), KM_SLEEP);

	q = bufq->bq_private;
	for (i = 0; i < PRIOCSCAN_NQUEUE; i++) {
		struct cscan_queue *cq = &q->bq_queue[i].q_queue;

		cscan_init(cq);
	}
}