/*      $NetBSD: bufq_priocscan.c,v 1.22 2025/12/10 21:33:01 andvar Exp $       */

/*-
 * Copyright (c)2004,2005,2006,2008,2009,2011,2012 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 1.22 2025/12/10 21:33:01 andvar 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>
#include <sys/rbtree.h>
#include <sys/module.h>

#undef  PRIOCSCAN_USE_GLOBAL_POSITION

/*
 * Cyclical scan (CSCAN)
 */

struct cscan_key {
        daddr_t k_rawblkno;
        int k_cylinder;
};

struct cscan_queue {
        rb_tree_t cq_buffers;           /* ordered list of buffers */
#if !defined(PRIOCSCAN_USE_GLOBAL_POSITION)
        struct cscan_key cq_lastkey;    /* key of last request */
#endif /* !defined(PRIOCSCAN_USE_GLOBAL_POSITION) */
        int cq_sortby;                  /* BUFQ_SORT_MASK */
        rb_tree_ops_t cq_ops;
};

static signed int
buf_cmp(const struct buf *b1, const struct buf *b2, int sortby)
{

        if (buf_inorder(b2, b1, sortby)) {
                return 1;       /* b1 > b2 */
        }
        if (buf_inorder(b1, b2, sortby)) {
                return -1;      /* b1 < b2 */
        }
        return 0;
}

/* return positive if n1 > n2 */
static signed int
cscan_tree_compare_nodes(void *context, const void *n1, const void *n2)
{
        const struct cscan_queue * const q = context;
        const struct buf * const b1 = n1;
        const struct buf * const b2 = n2;
        const int sortby = q->cq_sortby;
        const int diff = buf_cmp(b1, b2, sortby);

        /*
         * XXX rawblkno/cylinder might not be unique.  eg. unbuffered i/o
         */

        if (diff != 0) {
                return diff;
        }

        /*
         * XXX rawblkno/cylinder might not be unique.  eg. unbuffered i/o
         */
        if (b1 > b2) {
                return 1;
        }
        if (b1 < b2) {
                return -1;
        }
        return 0;
}

/* return positive if n1 > k2 */
static signed int
cscan_tree_compare_key(void *context, const void *n1, const void *k2)
{
        const struct cscan_queue * const q = context;
        const struct buf * const b1 = n1;
        const struct cscan_key * const key = k2;
        const struct buf tmp = {
                .b_rawblkno = key->k_rawblkno,
                .b_cylinder = key->k_cylinder,
        };
        const struct buf *b2 = &tmp;
        const int sortby = q->cq_sortby;

        return buf_cmp(b1, b2, sortby);
}

static void __unused
cscan_dump(struct cscan_queue *cq)
{
        const int sortby = cq->cq_sortby;
        struct buf *bp;

        RB_TREE_FOREACH(bp, &cq->cq_buffers) {
                if (sortby == BUFQ_SORT_RAWBLOCK) {
                        printf(" %jd", (intmax_t)bp->b_rawblkno);
                } else {
                        printf(" %jd/%jd",
                            (intmax_t)bp->b_cylinder, (intmax_t)bp->b_rawblkno);
                }
        }
}

static inline bool
cscan_empty(struct cscan_queue *q)
{

        /* XXX this might do more work than necessary */
        return rb_tree_iterate(&q->cq_buffers, NULL, RB_DIR_LEFT) == NULL;
}

static void
cscan_put(struct cscan_queue *q, struct buf *bp)
{
        struct buf *obp __diagused;

        obp = rb_tree_insert_node(&q->cq_buffers, bp);
        KASSERT(obp == bp); /* see cscan_tree_compare_nodes */
}

static struct buf *
cscan_get(struct cscan_queue *q, int remove, struct cscan_key *key)
{
        struct buf *bp;

        bp = rb_tree_find_node_geq(&q->cq_buffers, key);
        KDASSERT(bp == NULL || cscan_tree_compare_key(q, bp, key) >= 0);
        if (bp == NULL) {
                bp = rb_tree_iterate(&q->cq_buffers, NULL, RB_DIR_LEFT);
                KDASSERT(cscan_tree_compare_key(q, bp, key) < 0);
        }
        if (bp != NULL && remove) {
#if defined(DEBUG)
                struct buf *nbp;
#endif /* defined(DEBUG) */

                rb_tree_remove_node(&q->cq_buffers, bp);
                /*
                 * remember the head position.
                 */
                key->k_cylinder = bp->b_cylinder;
                key->k_rawblkno = bp->b_rawblkno + (bp->b_bcount >> DEV_BSHIFT);
#if defined(DEBUG)
                nbp = rb_tree_find_node_geq(&q->cq_buffers, key);
                if (nbp != NULL && cscan_tree_compare_nodes(q, nbp, bp) < 0) {
                        panic("%s: wrong order %p < %p\n", __func__,
                            nbp, bp);
                }
#endif /* defined(DEBUG) */
        }
        return bp;
}

static void
cscan_init(struct cscan_queue *q, int sortby)
{
        static const rb_tree_ops_t cscan_tree_ops = {
                .rbto_compare_nodes = cscan_tree_compare_nodes,
                .rbto_compare_key = cscan_tree_compare_key,
                .rbto_node_offset = offsetof(struct buf, b_u.u_rbnode),
                .rbto_context = NULL,
        };

        q->cq_sortby = sortby;
        /* XXX copy ops to workaround rbtree.h API limitation */
        q->cq_ops = cscan_tree_ops;
        q->cq_ops.rbto_context = q;
        rb_tree_init(&q->cq_buffers, &q->cq_ops);
}

/*
 * Per-priority 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 defined(PRIOCSCAN_USE_GLOBAL_POSITION)
        /*
         * XXX using "global" head position can reduce positioning time
         * when switching between queues.
         * although it might affect against fairness.
         */
        struct cscan_key bq_lastkey;
#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_private(bufq);
        struct cscan_queue *cq;

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

static struct buf *
bufq_priocscan_get(struct bufq_state *bufq, int remove)
{
        struct bufq_priocscan *q = bufq_private(bufq);
        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?
                 */
                if (remove) {
                        KASSERT(pq->q_burst > 0);
                        pq->q_burst--;
                }
        }

        /*
         * finally, get a request from the selected queue.
         */
        KDASSERT(!cscan_empty(&pq->q_queue));
        bp = cscan_get(&pq->q_queue, remove,
#if defined(PRIOCSCAN_USE_GLOBAL_POSITION)
            &q->bq_lastkey
#else /* defined(PRIOCSCAN_USE_GLOBAL_POSITION) */
            &pq->q_queue.cq_lastkey
#endif /* defined(PRIOCSCAN_USE_GLOBAL_POSITION) */
            );
        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_private(bufq);
        unsigned int i;

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

                /*
                 * XXX probably could be faster but the cancel functionality
                 * is not widely used anyway.
                 */
                RB_TREE_FOREACH(it, &cq->cq_buffers) {
                        if (it == bp) {
                                rb_tree_remove_node(&cq->cq_buffers, bp);
                                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;
        const int sortby = bufq->bq_flags & BUFQ_SORT_MASK;
        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, sortby);
        }
}

MODULE(MODULE_CLASS_BUFQ, bufq_priocscan, NULL);

static int
bufq_priocscan_modcmd(modcmd_t cmd, void *opaque)
{

        switch (cmd) {
        case MODULE_CMD_INIT:
                return bufq_register(&bufq_strat_priocscan);
        case MODULE_CMD_FINI:
                return bufq_unregister(&bufq_strat_priocscan);
        default:
                return ENOTTY;
        }
}