linux-imx

/*

 * buffered writeback throttling. loosely based on CoDel. We can't drop

 * packets for IO scheduling, so the logic is something like this:

 *

 * - Monitor latencies in a defined window of time.

 * - If the minimum latency in the above window exceeds some target, increment

 *   scaling step and scale down queue depth by a factor of 2x. The monitoring

 *   window is then shrunk to 100 / sqrt(scaling step + 1).

 * - For any window where we don't have solid data on what the latencies

 *   look like, retain status quo.

 * - If latencies look good, decrement scaling step.

 * - If we're only doing writes, allow the scaling step to go negative. This

 *   will temporarily boost write performance, snapping back to a stable

 *   scaling step of 0 if reads show up or the heavy writers finish. Unlike

 *   positive scaling steps where we shrink the monitoring window, a negative

 *   scaling step retains the default step==0 window size.

 *

 * Copyright (C) 2016 Jens Axboe

 *

 */

#include <linux/kernel.h>

#include <linux/blk_types.h>

#include <linux/slab.h>

#include <linux/backing-dev.h>

#include <linux/swap.h>

​

#include "blk-wbt.h"

#include "blk-rq-qos.h"

​

#define CREATE_TRACE_POINTS

#include <trace/events/wbt.h>

​

static inline void wbt_clear_state(struct request *rq)

{

    rq->wbt_flags = 0;

}

​

static inline enum wbt_flags wbt_flags(struct request *rq)

{

    return rq->wbt_flags;

}

​

static inline bool wbt_is_tracked(struct request *rq)

{

    return rq->wbt_flags & WBT_TRACKED;

}

​

static inline bool wbt_is_read(struct request *rq)

{

    return rq->wbt_flags & WBT_READ;

}

​

enum {

    /*

     * Default setting, we'll scale up (to 75% of QD max) or down (min 1)

     * from here depending on device stats

     */

    RWB_DEF_DEPTH   = 16,

​

    /*

     * 100msec window

     */

    RWB_WINDOW_NSEC     = 100 * 1000 * 1000ULL,