/*
 * Copyright (C) 2016 CNEX Labs
 * Initial release: Javier Gonzalez <javier@cnexlabs.com>
 *                  Matias Bjorling <matias@cnexlabs.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * pblk-rl.c - pblk's rate limiter for user I/O
 *
 */

#include "pblk.h"

static void pblk_rl_kick_u_timer(struct pblk_rl *rl)
{
        mod_timer(&rl->u_timer, jiffies + msecs_to_jiffies(5000));
}

int pblk_rl_is_limit(struct pblk_rl *rl)
{
        int rb_space;

        rb_space = atomic_read(&rl->rb_space);

        return (rb_space == 0);
}

int pblk_rl_user_may_insert(struct pblk_rl *rl, int nr_entries)
{
        int rb_user_cnt = atomic_read(&rl->rb_user_cnt);
        int rb_space = atomic_read(&rl->rb_space);

        if (unlikely(rb_space >= 0) && (rb_space - nr_entries < 0))
                return NVM_IO_ERR;

        if (rb_user_cnt >= rl->rb_user_max)
                return NVM_IO_REQUEUE;

        return NVM_IO_OK;
}

void pblk_rl_inserted(struct pblk_rl *rl, int nr_entries)
{
        int rb_space = atomic_read(&rl->rb_space);

        if (unlikely(rb_space >= 0))
                atomic_sub(nr_entries, &rl->rb_space);
}

int pblk_rl_gc_may_insert(struct pblk_rl *rl, int nr_entries)
{
        int rb_gc_cnt = atomic_read(&rl->rb_gc_cnt);
        int rb_user_active;

        /* If there is no user I/O let GC take over space on the write buffer */
        rb_user_active = READ_ONCE(rl->rb_user_active);
        return (!(rb_gc_cnt >= rl->rb_gc_max && rb_user_active));
}

void pblk_rl_user_in(struct pblk_rl *rl, int nr_entries)
{
        atomic_add(nr_entries, &rl->rb_user_cnt);

        /* Release user I/O state. Protect from GC */
        smp_store_release(&rl->rb_user_active, 1);
        pblk_rl_kick_u_timer(rl);
}

void pblk_rl_gc_in(struct pblk_rl *rl, int nr_entries)
{
        atomic_add(nr_entries, &rl->rb_gc_cnt);
}

void pblk_rl_out(struct pblk_rl *rl, int nr_user, int nr_gc)
{
        atomic_sub(nr_user, &rl->rb_user_cnt);
        atomic_sub(nr_gc, &rl->rb_gc_cnt);
}

unsigned long pblk_rl_nr_free_blks(struct pblk_rl *rl)
{
        return atomic_read(&rl->free_blocks);
}

/*
 * We check for (i) the number of free blocks in the current LUN and (ii) the
 * total number of free blocks in the pblk instance. This is to even out the
 * number of free blocks on each LUN when GC kicks in.
 *
 * Only the total number of free blocks is used to configure the rate limiter.
 */
void pblk_rl_update_rates(struct pblk_rl *rl)
{
        struct pblk *pblk = container_of(rl, struct pblk, rl);
        unsigned long free_blocks = pblk_rl_nr_free_blks(rl);
        int max = rl->rb_budget;

        if (free_blocks >= rl->high) {
                rl->rb_user_max = max;
                rl->rb_gc_max = 0;
                rl->rb_state = PBLK_RL_HIGH;
        } else if (free_blocks < rl->high) {
                int shift = rl->high_pw - rl->rb_windows_pw;
                int user_windows = free_blocks >> shift;
                int user_max = user_windows << PBLK_MAX_REQ_ADDRS_PW;

                rl->rb_user_max = user_max;
                rl->rb_gc_max = max - user_max;

                if (free_blocks <= rl->rsv_blocks) {
                        rl->rb_user_max = 0;
                        rl->rb_gc_max = max;
                }

                /* In the worst case, we will need to GC lines in the low list
                 * (high valid sector count). If there are lines to GC on high
                 * or mid lists, these will be prioritized
                 */
                rl->rb_state = PBLK_RL_LOW;
        }

        if (rl->rb_state == (PBLK_RL_MID | PBLK_RL_LOW))
                pblk_gc_should_start(pblk);
        else
                pblk_gc_should_stop(pblk);
}

void pblk_rl_free_lines_inc(struct pblk_rl *rl, struct pblk_line *line)
{
        int blk_in_line = atomic_read(&line->blk_in_line);

        atomic_add(blk_in_line, &rl->free_blocks);
        pblk_rl_update_rates(rl);
}

void pblk_rl_free_lines_dec(struct pblk_rl *rl, struct pblk_line *line)
{
        int blk_in_line = atomic_read(&line->blk_in_line);

        atomic_sub(blk_in_line, &rl->free_blocks);
        pblk_rl_update_rates(rl);
}

int pblk_rl_high_thrs(struct pblk_rl *rl)
{
        return rl->high;
}

int pblk_rl_max_io(struct pblk_rl *rl)
{
        return rl->rb_max_io;
}

static void pblk_rl_u_timer(struct timer_list *t)
{
        struct pblk_rl *rl = from_timer(rl, t, u_timer);

        /* Release user I/O state. Protect from GC */
        smp_store_release(&rl->rb_user_active, 0);
}

void pblk_rl_free(struct pblk_rl *rl)
{
        del_timer(&rl->u_timer);
}

void pblk_rl_init(struct pblk_rl *rl, int budget)
{
        struct pblk *pblk = container_of(rl, struct pblk, rl);
        struct pblk_line_meta *lm = &pblk->lm;
        int min_blocks = lm->blk_per_line * PBLK_GC_RSV_LINE;
        unsigned int rb_windows;

        rl->high = rl->total_blocks / PBLK_USER_HIGH_THRS;
        rl->high_pw = get_count_order(rl->high);

        rl->low = rl->total_blocks / PBLK_USER_LOW_THRS;
        if (rl->low < min_blocks)
                rl->low = min_blocks;

        rl->rsv_blocks = min_blocks;

        /* This will always be a power-of-2 */
        rb_windows = budget / PBLK_MAX_REQ_ADDRS;
        rl->rb_windows_pw = get_count_order(rb_windows);

        /* To start with, all buffer is available to user I/O writers */
        rl->rb_budget = budget;
        rl->rb_user_max = budget;
        rl->rb_max_io = budget >> 1;
        rl->rb_gc_max = 0;
        rl->rb_state = PBLK_RL_HIGH;

        atomic_set(&rl->rb_user_cnt, 0);
        atomic_set(&rl->rb_gc_cnt, 0);
        atomic_set(&rl->rb_space, -1);

        timer_setup(&rl->u_timer, pblk_rl_u_timer, 0);

        rl->rb_user_active = 0;
        rl->rb_gc_active = 0;
}