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DEFINITIONS
This source file includes following definitions.
- free_as_io_context
- as_trim
- exit_as_io_context
- alloc_as_io_context
- as_get_io_context
- as_put_io_context
- as_add_rq_rb
- as_del_rq_rb
- as_choose_req
- as_find_next_rq
- as_antic_expired
- as_antic_waitnext
- as_antic_waitreq
- as_antic_stop
- as_antic_timeout
- as_update_thinktime
- as_update_seekdist
- as_update_iohist
- as_close_req
- as_can_break_anticipation
- as_can_anticipate
- as_update_rq
- update_write_batch
- as_completed_request
- as_remove_queued_request
- as_fifo_expired
- as_batch_expired
- as_move_to_dispatch
- as_dispatch_request
- as_add_request
- as_activate_request
- as_deactivate_request
- as_queue_empty
- as_merge
- as_merged_request
- as_merged_requests
- as_work_handler
- as_may_queue
- as_exit_queue
- as_init_queue
- as_var_show
- as_var_store
- est_time_show
- as_init
- as_exit
/*
* Anticipatory & deadline i/o scheduler.
*
* Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
* Nick Piggin <nickpiggin@yahoo.com.au>
*
*/
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/interrupt.h>
#define REQ_SYNC 1
#define REQ_ASYNC 0
/*
* See Documentation/block/as-iosched.txt
*/
/*
* max time before a read is submitted.
*/
#define default_read_expire (HZ / 8)
/*
* ditto for writes, these limits are not hard, even
* if the disk is capable of satisfying them.
*/
#define default_write_expire (HZ / 4)
/*
* read_batch_expire describes how long we will allow a stream of reads to
* persist before looking to see whether it is time to switch over to writes.
*/
#define default_read_batch_expire (HZ / 2)
/*
* write_batch_expire describes how long we want a stream of writes to run for.
* This is not a hard limit, but a target we set for the auto-tuning thingy.
* See, the problem is: we can send a lot of writes to disk cache / TCQ in
* a short amount of time...
*/
#define default_write_batch_expire (HZ / 8)
/*
* max time we may wait to anticipate a read (default around 6ms)
*/
#define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
/*
* Keep track of up to 20ms thinktimes. We can go as big as we like here,
* however huge values tend to interfere and not decay fast enough. A program
* might be in a non-io phase of operation. Waiting on user input for example,
* or doing a lengthy computation. A small penalty can be justified there, and
* will still catch out those processes that constantly have large thinktimes.
*/
#define MAX_THINKTIME (HZ/50UL)
/* Bits in as_io_context.state */
enum as_io_states {
AS_TASK_RUNNING=0, /* Process has not exited */
AS_TASK_IOSTARTED, /* Process has started some IO */
AS_TASK_IORUNNING, /* Process has completed some IO */
};
enum anticipation_status {
ANTIC_OFF=0, /* Not anticipating (normal operation) */
ANTIC_WAIT_REQ, /* The last read has not yet completed */
ANTIC_WAIT_NEXT, /* Currently anticipating a request vs
last read (which has completed) */
ANTIC_FINISHED, /* Anticipating but have found a candidate
* or timed out */
};
struct as_data {
/*
* run time data
*/
struct request_queue *q; /* the "owner" queue */
/*
* requests (as_rq s) are present on both sort_list and fifo_list
*/
struct rb_root sort_list[2];
struct list_head fifo_list[2];
struct request *next_rq[2]; /* next in sort order */
sector_t last_sector[2]; /* last REQ_SYNC & REQ_ASYNC sectors */
unsigned long exit_prob; /* probability a task will exit while
being waited on */
unsigned long exit_no_coop; /* probablility an exited task will
not be part of a later cooperating
request */
unsigned long new_ttime_total; /* mean thinktime on new proc */
unsigned long new_ttime_mean;
u64 new_seek_total; /* mean seek on new proc */
sector_t new_seek_mean;
unsigned long current_batch_expires;
unsigned long last_check_fifo[2];
int changed_batch; /* 1: waiting for old batch to end */
int new_batch; /* 1: waiting on first read complete */
int batch_data_dir; /* current batch REQ_SYNC / REQ_ASYNC */
int write_batch_count; /* max # of reqs in a write batch */
int current_write_count; /* how many requests left this batch */
int write_batch_idled; /* has the write batch gone idle? */
enum anticipation_status antic_status;
unsigned long antic_start; /* jiffies: when it started */
struct timer_list antic_timer; /* anticipatory scheduling timer */
struct work_struct antic_work; /* Deferred unplugging */
struct io_context *io_context; /* Identify the expected process */
int ioc_finished; /* IO associated with io_context is finished */
int nr_dispatched;
/*
* settings that change how the i/o scheduler behaves
*/
unsigned long fifo_expire[2];
unsigned long batch_expire[2];
unsigned long antic_expire;
};
/*
* per-request data.
*/
enum arq_state {
AS_RQ_NEW=0, /* New - not referenced and not on any lists */
AS_RQ_QUEUED, /* In the request queue. It belongs to the
scheduler */
AS_RQ_DISPATCHED, /* On the dispatch list. It belongs to the
driver now */
AS_RQ_PRESCHED, /* Debug poisoning for requests being used */
AS_RQ_REMOVED,
AS_RQ_MERGED,
AS_RQ_POSTSCHED, /* when they shouldn't be */
};
#define RQ_IOC(rq) ((struct io_context *) (rq)->elevator_private)
#define RQ_STATE(rq) ((enum arq_state)(rq)->elevator_private2)
#define RQ_SET_STATE(rq, state) ((rq)->elevator_private2 = (void *) state)
static DEFINE_PER_CPU(unsigned long, ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);
static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
static void as_antic_stop(struct as_data *ad);
/*
* IO Context helper functions
*/
/* Called to deallocate the as_io_context */
static void free_as_io_context(struct as_io_context *aic)
{
kfree(aic);
elv_ioc_count_dec(ioc_count);
if (ioc_gone) {
/*
* AS scheduler is exiting, grab exit lock and check
* the pending io context count. If it hits zero,
* complete ioc_gone and set it back to NULL.
*/
spin_lock(&ioc_gone_lock);
if (ioc_gone && !elv_ioc_count_read(ioc_count)) {
complete(ioc_gone);
ioc_gone = NULL;
}
spin_unlock(&ioc_gone_lock);
}
}
static void as_trim(struct io_context *ioc)
{
spin_lock_irq(&ioc->lock);
if (ioc->aic)
free_as_io_context(ioc->aic);
ioc->aic = NULL;
spin_unlock_irq(&ioc->lock);
}
/* Called when the task exits */
static void exit_as_io_context(struct as_io_context *aic)
{
WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state));
clear_bit(AS_TASK_RUNNING, &aic->state);
}
static struct as_io_context *alloc_as_io_context(void)
{
struct as_io_context *ret;
ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
if (ret) {
ret->dtor = free_as_io_context;
ret->exit = exit_as_io_context;
ret->state = 1 << AS_TASK_RUNNING;
atomic_set(&ret->nr_queued, 0);
atomic_set(&ret->nr_dispatched, 0);
spin_lock_init(&ret->lock);
ret->ttime_total = 0;
ret->ttime_samples = 0;
ret->ttime_mean = 0;
ret->seek_total = 0;
ret->seek_samples = 0;
ret->seek_mean = 0;
elv_ioc_count_inc(ioc_count);
}
return ret;
}
/*
* If the current task has no AS IO context then create one and initialise it.
* Then take a ref on the task's io context and return it.
*/
static struct io_context *as_get_io_context(int node)
{
struct io_context *ioc = get_io_context(GFP_ATOMIC, node);
if (ioc && !ioc->aic) {
ioc->aic = alloc_as_io_context();
if (!ioc->aic) {
put_io_context(ioc);
ioc = NULL;
}
}
return ioc;
}
static void as_put_io_context(struct request *rq)
{
struct as_io_context *aic;
if (unlikely(!RQ_IOC(rq)))
return;
aic = RQ_IOC(rq)->aic;
if (rq_is_sync(rq) && aic) {
unsigned long flags;
spin_lock_irqsave(&aic->lock, flags);
set_bit(AS_TASK_IORUNNING, &aic->state);
aic->last_end_request = jiffies;
spin_unlock_irqrestore(&aic->lock, flags);
}
put_io_context(RQ_IOC(rq));
}
/*
* rb tree support functions
*/
#define RQ_RB_ROOT(ad, rq) (&(ad)->sort_list[rq_is_sync((rq))])
static void as_add_rq_rb(struct as_data *ad, struct request *rq)
{
struct request *alias;
while ((unlikely(alias = elv_rb_add(RQ_RB_ROOT(ad, rq), rq)))) {
as_move_to_dispatch(ad, alias);
as_antic_stop(ad);
}
}
static inline void as_del_rq_rb(struct as_data *ad, struct request *rq)
{
elv_rb_del(RQ_RB_ROOT(ad, rq), rq);
}
/*
* IO Scheduler proper
*/
#define MAXBACK (1024 * 1024) /*
* Maximum distance the disk will go backward
* for a request.
*/
#define BACK_PENALTY 2
/*
* as_choose_req selects the preferred one of two requests of the same data_dir
* ignoring time - eg. timeouts, which is the job of as_dispatch_request
*/
static struct request *
as_choose_req(struct as_data *ad, struct request *rq1, struct request *rq2)
{
int data_dir;
sector_t last, s1, s2, d1, d2;
int r1_wrap=0, r2_wrap=0; /* requests are behind the disk head */
const sector_t maxback = MAXBACK;
if (rq1 == NULL || rq1 == rq2)
return rq2;
if (rq2 == NULL)
return rq1;
data_dir = rq_is_sync(rq1);
last = ad->last_sector[data_dir];
s1 = rq1->sector;
s2 = rq2->sector;
BUG_ON(data_dir != rq_is_sync(rq2));
/*
* Strict one way elevator _except_ in the case where we allow
* short backward seeks which are biased as twice the cost of a
* similar forward seek.
*/
if (s1 >= last)
d1 = s1 - last;
else if (s1+maxback >= last)
d1 = (last - s1)*BACK_PENALTY;
else {
r1_wrap = 1;
d1 = 0; /* shut up, gcc */
}
if (s2 >= last)
d2 = s2 - last;
else if (s2+maxback >= last)
d2 = (last - s2)*BACK_PENALTY;
else {
r2_wrap = 1;
d2 = 0;
}
/* Found required data */
if (!r1_wrap && r2_wrap)
return rq1;
else if (!r2_wrap && r1_wrap)
return rq2;
else if (r1_wrap && r2_wrap) {
/* both behind the head */
if (s1 <= s2)
return rq1;
else
return rq2;
}
/* Both requests in front of the head */
if (d1 < d2)
return rq1;
else if (d2 < d1)
return rq2;
else {
if (s1 >= s2)
return rq1;
else
return rq2;
}
}
/*
* as_find_next_rq finds the next request after @prev in elevator order.
* this with as_choose_req form the basis for how the scheduler chooses
* what request to process next. Anticipation works on top of this.
*/
static struct request *
as_find_next_rq(struct as_data *ad, struct request *last)
{
struct rb_node *rbnext = rb_next(&last->rb_node);
struct rb_node *rbprev = rb_prev(&last->rb_node);
struct request *next = NULL, *prev = NULL;
BUG_ON(RB_EMPTY_NODE(&last->rb_node));
if (rbprev)
prev = rb_entry_rq(rbprev);
if (rbnext)
next = rb_entry_rq(rbnext);
else {
const int data_dir = rq_is_sync(last);
rbnext = rb_first(&ad->sort_list[data_dir]);
if (rbnext && rbnext != &last->rb_node)
next = rb_entry_rq(rbnext);
}
return as_choose_req(ad, next, prev);
}
/*
* anticipatory scheduling functions follow
*/
/*
* as_antic_expired tells us when we have anticipated too long.
* The funny "absolute difference" math on the elapsed time is to handle
* jiffy wraps, and disks which have been idle for 0x80000000 jiffies.
*/
static int as_antic_expired(struct as_data *ad)
{
long delta_jif;
delta_jif = jiffies - ad->antic_start;
if (unlikely(delta_jif < 0))
delta_jif = -delta_jif;
if (delta_jif < ad->antic_expire)
return 0;
return 1;
}
/*
* as_antic_waitnext starts anticipating that a nice request will soon be
* submitted. See also as_antic_waitreq
*/
static void as_antic_waitnext(struct as_data *ad)
{
unsigned long timeout;
BUG_ON(ad->antic_status != ANTIC_OFF
&& ad->antic_status != ANTIC_WAIT_REQ);
timeout = ad->antic_start + ad->antic_expire;
mod_timer(&ad->antic_timer, timeout);
ad->antic_status = ANTIC_WAIT_NEXT;
}
/*
* as_antic_waitreq starts anticipating. We don't start timing the anticipation
* until the request that we're anticipating on has finished. This means we
* are timing from when the candidate process wakes up hopefully.
*/
static void as_antic_waitreq(struct as_data *ad)
{
BUG_ON(ad->antic_status == ANTIC_FINISHED);
if (ad->antic_status == ANTIC_OFF) {
if (!ad->io_context || ad->ioc_finished)
as_antic_waitnext(ad);
else
ad->antic_status = ANTIC_WAIT_REQ;
}
}
/*
* This is called directly by the functions in this file to stop anticipation.
* We kill the timer and schedule a call to the request_fn asap.
*/
static void as_antic_stop(struct as_data *ad)
{
int status = ad->antic_status;
if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
if (status == ANTIC_WAIT_NEXT)
del_timer(&ad->antic_timer);
ad->antic_status = ANTIC_FINISHED;
/* see as_work_handler */
kblockd_schedule_work(ad->q, &ad->antic_work);
}
}
/*
* as_antic_timeout is the timer function set by as_antic_waitnext.
*/
static void as_antic_timeout(unsigned long data)
{
struct request_queue *q = (struct request_queue *)data;
struct as_data *ad = q->elevator->elevator_data;
unsigned long flags;
spin_lock_irqsave(q->queue_lock, flags);
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
struct as_io_context *aic;
spin_lock(&ad->io_context->lock);
aic = ad->io_context->aic;
ad->antic_status = ANTIC_FINISHED;
kblockd_schedule_work(q, &ad->antic_work);
if (aic->ttime_samples == 0) {
/* process anticipated on has exited or timed out*/
ad->exit_prob = (7*ad->exit_prob + 256)/8;
}
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
/* process not "saved" by a cooperating request */
ad->exit_no_coop = (7*ad->exit_no_coop + 256)/8;
}
spin_unlock(&ad->io_context->lock);
}
spin_unlock_irqrestore(q->queue_lock, flags);
}
static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic,
unsigned long ttime)
{
/* fixed point: 1.0 == 1<<8 */
if (aic->ttime_samples == 0) {
ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
ad->new_ttime_mean = ad->new_ttime_total / 256;
ad->exit_prob = (7*ad->exit_prob)/8;
}
aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
}
static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic,
sector_t sdist)
{
u64 total;
if (aic->seek_samples == 0) {
ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
ad->new_seek_mean = ad->new_seek_total / 256;
}
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
*/
if (aic->seek_samples <= 60) /* second&third seek */
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
else
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
aic->seek_samples = (7*aic->seek_samples + 256) / 8;
aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
total = aic->seek_total + (aic->seek_samples/2);
do_div(total, aic->seek_samples);
aic->seek_mean = (sector_t)total;
}
/*
* as_update_iohist keeps a decaying histogram of IO thinktimes, and
* updates @aic->ttime_mean based on that. It is called when a new
* request is queued.
*/
static void as_update_iohist(struct as_data *ad, struct as_io_context *aic,
struct request *rq)
{
int data_dir = rq_is_sync(rq);
unsigned long thinktime = 0;
sector_t seek_dist;
if (aic == NULL)
return;
if (data_dir == REQ_SYNC) {
unsigned long in_flight = atomic_read(&aic->nr_queued)
+ atomic_read(&aic->nr_dispatched);
spin_lock(&aic->lock);
if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
test_bit(AS_TASK_IOSTARTED, &aic->state)) {
/* Calculate read -> read thinktime */
if (test_bit(AS_TASK_IORUNNING, &aic->state)
&& in_flight == 0) {
thinktime = jiffies - aic->last_end_request;
thinktime = min(thinktime, MAX_THINKTIME-1);
}
as_update_thinktime(ad, aic, thinktime);
/* Calculate read -> read seek distance */
if (aic->last_request_pos < rq->sector)
seek_dist = rq->sector - aic->last_request_pos;
else
seek_dist = aic->last_request_pos - rq->sector;
as_update_seekdist(ad, aic, seek_dist);
}
aic->last_request_pos = rq->sector + rq->nr_sectors;
set_bit(AS_TASK_IOSTARTED, &aic->state);
spin_unlock(&aic->lock);
}
}
/*
* as_close_req decides if one request is considered "close" to the
* previous one issued.
*/
static int as_close_req(struct as_data *ad, struct as_io_context *aic,
struct request *rq)
{
unsigned long delay; /* jiffies */
sector_t last = ad->last_sector[ad->batch_data_dir];
sector_t next = rq->sector;
sector_t delta; /* acceptable close offset (in sectors) */
sector_t s;
if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
delay = 0;
else
delay = jiffies - ad->antic_start;
if (delay == 0)
delta = 8192;
else if (delay <= (20 * HZ / 1000) && delay <= ad->antic_expire)
delta = 8192 << delay;
else
return 1;
if ((last <= next + (delta>>1)) && (next <= last + delta))
return 1;
if (last < next)
s = next - last;
else
s = last - next;
if (aic->seek_samples == 0) {
/*
* Process has just started IO. Use past statistics to
* gauge success possibility
*/
if (ad->new_seek_mean > s) {
/* this request is better than what we're expecting */
return 1;
}
} else {
if (aic->seek_mean > s) {
/* this request is better than what we're expecting */
return 1;
}
}
return 0;
}
/*
* as_can_break_anticipation returns true if we have been anticipating this
* request.
*
* It also returns true if the process against which we are anticipating
* submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
* dispatch it ASAP, because we know that application will not be submitting
* any new reads.
*
* If the task which has submitted the request has exited, break anticipation.
*
* If this task has queued some other IO, do not enter enticipation.
*/
static int as_can_break_anticipation(struct as_data *ad, struct request *rq)
{
struct io_context *ioc;
struct as_io_context *aic;
ioc = ad->io_context;
BUG_ON(!ioc);
spin_lock(&ioc->lock);
if (rq && ioc == RQ_IOC(rq)) {
/* request from same process */
spin_unlock(&ioc->lock);
return 1;
}
if (ad->ioc_finished && as_antic_expired(ad)) {
/*
* In this situation status should really be FINISHED,
* however the timer hasn't had the chance to run yet.
*/
spin_unlock(&ioc->lock);
return 1;
}
aic = ioc->aic;
if (!aic) {
spin_unlock(&ioc->lock);
return 0;
}
if (atomic_read(&aic->nr_queued) > 0) {
/* process has more requests queued */
spin_unlock(&ioc->lock);
return 1;
}
if (atomic_read(&aic->nr_dispatched) > 0) {
/* process has more requests dispatched */
spin_unlock(&ioc->lock);
return 1;
}
if (rq && rq_is_sync(rq) && as_close_req(ad, aic, rq)) {
/*
* Found a close request that is not one of ours.
*
* This makes close requests from another process update
* our IO history. Is generally useful when there are
* two or more cooperating processes working in the same
* area.
*/
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
if (aic->ttime_samples == 0)
ad->exit_prob = (7*ad->exit_prob + 256)/8;
ad->exit_no_coop = (7*ad->exit_no_coop)/8;
}
as_update_iohist(ad, aic, rq);
spin_unlock(&ioc->lock);
return 1;
}
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
/* process anticipated on has exited */
if (aic->ttime_samples == 0)
ad->exit_prob = (7*ad->exit_prob + 256)/8;
if (ad->exit_no_coop > 128) {
spin_unlock(&ioc->lock);
return 1;
}
}
if (aic->ttime_samples == 0) {
if (ad->new_ttime_mean > ad->antic_expire) {
spin_unlock(&ioc->lock);
return 1;
}
if (ad->exit_prob * ad->exit_no_coop > 128*256) {
spin_unlock(&ioc->lock);
return 1;
}
} else if (aic->ttime_mean > ad->antic_expire) {
/* the process thinks too much between requests */
spin_unlock(&ioc->lock);
return 1;
}
spin_unlock(&ioc->lock);
return 0;
}
/*
* as_can_anticipate indicates whether we should either run rq
* or keep anticipating a better request.
*/
static int as_can_anticipate(struct as_data *ad, struct request *rq)
{
#if 0 /* disable for now, we need to check tag level as well */
/*
* SSD device without seek penalty, disable idling
*/
if (blk_queue_nonrot(ad->q)) axman
return 0;
#endif
if (!ad->io_context)
/*
* Last request submitted was a write
*/
return 0;
if (ad->antic_status == ANTIC_FINISHED)
/*
* Don't restart if we have just finished. Run the next request
*/
return 0;
if (as_can_break_anticipation(ad, rq))
/*
* This request is a good candidate. Don't keep anticipating,
* run it.
*/
return 0;
/*
* OK from here, we haven't finished, and don't have a decent request!
* Status is either ANTIC_OFF so start waiting,
* ANTIC_WAIT_REQ so continue waiting for request to finish
* or ANTIC_WAIT_NEXT so continue waiting for an acceptable request.
*/
return 1;
}
/*
* as_update_rq must be called whenever a request (rq) is added to
* the sort_list. This function keeps caches up to date, and checks if the
* request might be one we are "anticipating"
*/
static void as_update_rq(struct as_data *ad, struct request *rq)
{
const int data_dir = rq_is_sync(rq);
/* keep the next_rq cache up to date */
ad->next_rq[data_dir] = as_choose_req(ad, rq, ad->next_rq[data_dir]);
/*
* have we been anticipating this request?
* or does it come from the same process as the one we are anticipating
* for?
*/
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
if (as_can_break_anticipation(ad, rq))
as_antic_stop(ad);
}
}
/*
* Gathers timings and resizes the write batch automatically
*/
static void update_write_batch(struct as_data *ad)
{
unsigned long batch = ad->batch_expire[REQ_ASYNC];
long write_time;
write_time = (jiffies - ad->current_batch_expires) + batch;
if (write_time < 0)
write_time = 0;
if (write_time > batch && !ad->write_batch_idled) {
if (write_time > batch * 3)
ad->write_batch_count /= 2;
else
ad->write_batch_count--;
} else if (write_time < batch && ad->current_write_count == 0) {
if (batch > write_time * 3)
ad->write_batch_count *= 2;
else
ad->write_batch_count++;
}
if (ad->write_batch_count < 1)
ad->write_batch_count = 1;
}
/*
* as_completed_request is to be called when a request has completed and
* returned something to the requesting process, be it an error or data.
*/
static void as_completed_request(struct request_queue *q, struct request *rq)
{
struct as_data *ad = q->elevator->elevator_data;
WARN_ON(!list_empty(&rq->queuelist));
if (RQ_STATE(rq) != AS_RQ_REMOVED) {
WARN(1, "rq->state %d\n", RQ_STATE(rq));
goto out;
}
if (ad->changed_batch && ad->nr_dispatched == 1) {
ad->current_batch_expires = jiffies +
ad->batch_expire[ad->batch_data_dir];
kblockd_schedule_work(q, &ad->antic_work);
ad->changed_batch = 0;
if (ad->batch_data_dir == REQ_SYNC)
ad->new_batch = 1;
}
WARN_ON(ad->nr_dispatched == 0);
ad->nr_dispatched--;
/*
* Start counting the batch from when a request of that direction is
* actually serviced. This should help devices with big TCQ windows
* and writeback caches
*/
if (ad->new_batch && ad->batch_data_dir == rq_is_sync(rq)) {
update_write_batch(ad);
ad->current_batch_expires = jiffies +
ad->batch_expire[REQ_SYNC];
ad->new_batch = 0;
}
if (ad->io_context == RQ_IOC(rq) && ad->io_context) {
ad->antic_start = jiffies;
ad->ioc_finished = 1;
if (ad->antic_status == ANTIC_WAIT_REQ) {
/*
* We were waiting on this request, now anticipate
* the next one
*/
as_antic_waitnext(ad);
}
}
as_put_io_context(rq);
out:
RQ_SET_STATE(rq, AS_RQ_POSTSCHED);
}
/*
* as_remove_queued_request removes a request from the pre dispatch queue
* without updating refcounts. It is expected the caller will drop the
* reference unless it replaces the request at somepart of the elevator
* (ie. the dispatch queue)
*/
static void as_remove_queued_request(struct request_queue *q,
struct request *rq)
{
const int data_dir = rq_is_sync(rq);
struct as_data *ad = q->elevator->elevator_data;
struct io_context *ioc;
WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);
ioc = RQ_IOC(rq);
if (ioc && ioc->aic) {
BUG_ON(!atomic_read(&ioc->aic->nr_queued));
atomic_dec(&ioc->aic->nr_queued);
}
/*
* Update the "next_rq" cache if we are about to remove its
* entry
*/
if (ad->next_rq[data_dir] == rq)
ad->next_rq[data_dir] = as_find_next_rq(ad, rq);
rq_fifo_clear(rq);
as_del_rq_rb(ad, rq);
}
/*
* as_fifo_expired returns 0 if there are no expired requests on the fifo,
* 1 otherwise. It is ratelimited so that we only perform the check once per
* `fifo_expire' interval. Otherwise a large number of expired requests
* would create a hopeless seekstorm.
*
* See as_antic_expired comment.
*/
static int as_fifo_expired(struct as_data *ad, int adir)
{
struct request *rq;
long delta_jif;
delta_jif = jiffies - ad->last_check_fifo[adir];
if (unlikely(delta_jif < 0))
delta_jif = -delta_jif;
if (delta_jif < ad->fifo_expire[adir])
return 0;
ad->last_check_fifo[adir] = jiffies;
if (list_empty(&ad->fifo_list[adir]))
return 0;
rq = rq_entry_fifo(ad->fifo_list[adir].next);
return time_after(jiffies, rq_fifo_time(rq));
}
/*
* as_batch_expired returns true if the current batch has expired. A batch
* is a set of reads or a set of writes.
*/
static inline int as_batch_expired(struct as_data *ad)
{
if (ad->changed_batch || ad->new_batch)
return 0;
if (ad->batch_data_dir == REQ_SYNC)
/* TODO! add a check so a complete fifo gets written? */
return time_after(jiffies, ad->current_batch_expires);
return time_after(jiffies, ad->current_batch_expires)
|| ad->current_write_count == 0;
}
/*
* move an entry to dispatch queue
*/
static void as_move_to_dispatch(struct as_data *ad, struct request *rq)
{
const int data_dir = rq_is_sync(rq);
BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
as_antic_stop(ad);
ad->antic_status = ANTIC_OFF;
/*
* This has to be set in order to be correctly updated by
* as_find_next_rq
*/
ad->last_sector[data_dir] = rq->sector + rq->nr_sectors;
if (data_dir == REQ_SYNC) {
struct io_context *ioc = RQ_IOC(rq);
/* In case we have to anticipate after this */
copy_io_context(&ad->io_context, &ioc);
} else {
if (ad->io_context) {
put_io_context(ad->io_context);
ad->io_context = NULL;
}
if (ad->current_write_count != 0)
ad->current_write_count--;
}
ad->ioc_finished = 0;
ad->next_rq[data_dir] = as_find_next_rq(ad, rq);
/*
* take it off the sort and fifo list, add to dispatch queue
*/
as_remove_queued_request(ad->q, rq);
WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);
elv_dispatch_sort(ad->q, rq);
RQ_SET_STATE(rq, AS_RQ_DISPATCHED);
if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
atomic_inc(&RQ_IOC(rq)->aic->nr_dispatched);
ad->nr_dispatched++;
}
/*
* as_dispatch_request selects the best request according to
* read/write expire, batch expire, etc, and moves it to the dispatch
* queue. Returns 1 if a request was found, 0 otherwise.
*/
static int as_dispatch_request(struct request_queue *q, int force)
{
struct as_data *ad = q->elevator->elevator_data;
const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]);
const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]);
struct request *rq;
if (unlikely(force)) {
/*
* Forced dispatch, accounting is useless. Reset
* accounting states and dump fifo_lists. Note that
* batch_data_dir is reset to REQ_SYNC to avoid
* screwing write batch accounting as write batch
* accounting occurs on W->R transition.
*/
int dispatched = 0;
ad->batch_data_dir = REQ_SYNC;
ad->changed_batch = 0;
ad->new_batch = 0;
while (ad->next_rq[REQ_SYNC]) {
as_move_to_dispatch(ad, ad->next_rq[REQ_SYNC]);
dispatched++;
}
ad->last_check_fifo[REQ_SYNC] = jiffies;
while (ad->next_rq[REQ_ASYNC]) {
as_move_to_dispatch(ad, ad->next_rq[REQ_ASYNC]);
dispatched++;
}
ad->last_check_fifo[REQ_ASYNC] = jiffies;
return dispatched;
}
/* Signal that the write batch was uncontended, so we can't time it */
if (ad->batch_data_dir == REQ_ASYNC && !reads) {
if (ad->current_write_count == 0 || !writes)
ad->write_batch_idled = 1;
}
if (!(reads || writes)
|| ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT
|| ad->changed_batch)
return 0;
if (!(reads && writes && as_batch_expired(ad))) {
/*
* batch is still running or no reads or no writes
*/
rq = ad->next_rq[ad->batch_data_dir];
if (ad->batch_data_dir == REQ_SYNC && ad->antic_expire) {
if (as_fifo_expired(ad, REQ_SYNC))
goto fifo_expired;
if (as_can_anticipate(ad, rq)) {
as_antic_waitreq(ad);
return 0;
}
}
if (rq) {
/* we have a "next request" */
if (reads && !writes)
ad->current_batch_expires =
jiffies + ad->batch_expire[REQ_SYNC];
goto dispatch_request;
}
}
/*
* at this point we are not running a batch. select the appropriate
* data direction (read / write)
*/
if (reads) {
BUG_ON(RB_EMPTY_ROOT(&ad->sort_list[REQ_SYNC]));
if (writes && ad->batch_data_dir == REQ_SYNC)
/*
* Last batch was a read, switch to writes
*/
goto dispatch_writes;
if (ad->batch_data_dir == REQ_ASYNC) {
WARN_ON(ad->new_batch);
ad->changed_batch = 1;
}
ad->batch_data_dir = REQ_SYNC;
rq = rq_entry_fifo(ad->fifo_list[REQ_SYNC].next);
ad->last_check_fifo[ad->batch_data_dir] = jiffies;
goto dispatch_request;
}
/*
* the last batch was a read
*/
if (writes) {
dispatch_writes:
BUG_ON(RB_EMPTY_ROOT(&ad->sort_list[REQ_ASYNC]));
if (ad->batch_data_dir == REQ_SYNC) {
ad->changed_batch = 1;
/*
* new_batch might be 1 when the queue runs out of
* reads. A subsequent submission of a write might
* cause a change of batch before the read is finished.
*/
ad->new_batch = 0;
}
ad->batch_data_dir = REQ_ASYNC;
ad->current_write_count = ad->write_batch_count;
ad->write_batch_idled = 0;
rq = rq_entry_fifo(ad->fifo_list[REQ_ASYNC].next);
ad->last_check_fifo[REQ_ASYNC] = jiffies;
goto dispatch_request;
}
BUG();
return 0;
dispatch_request:
/*
* If a request has expired, service it.
*/
if (as_fifo_expired(ad, ad->batch_data_dir)) {
fifo_expired:
rq = rq_entry_fifo(ad->fifo_list[ad->batch_data_dir].next);
}
if (ad->changed_batch) {
WARN_ON(ad->new_batch);
if (ad->nr_dispatched)
return 0;
if (ad->batch_data_dir == REQ_ASYNC)
ad->current_batch_expires = jiffies +
ad->batch_expire[REQ_ASYNC];
else
ad->new_batch = 1;
ad->changed_batch = 0;
}
/*
* rq is the selected appropriate request.
*/
as_move_to_dispatch(ad, rq);
return 1;
}
/*
* add rq to rbtree and fifo
*/
static void as_add_request(struct request_queue *q, struct request *rq)
{
struct as_data *ad = q->elevator->elevator_data;
int data_dir;
RQ_SET_STATE(rq, AS_RQ_NEW);
data_dir = rq_is_sync(rq);
rq->elevator_private = as_get_io_context(q->node);
if (RQ_IOC(rq)) {
as_update_iohist(ad, RQ_IOC(rq)->aic, rq);
atomic_inc(&RQ_IOC(rq)->aic->nr_queued);
}
as_add_rq_rb(ad, rq);
/*
* set expire time and add to fifo list
*/
rq_set_fifo_time(rq, jiffies + ad->fifo_expire[data_dir]);
list_add_tail(&rq->queuelist, &ad->fifo_list[data_dir]);
as_update_rq(ad, rq); /* keep state machine up to date */
RQ_SET_STATE(rq, AS_RQ_QUEUED);
}
static void as_activate_request(struct request_queue *q, struct request *rq)
{
WARN_ON(RQ_STATE(rq) != AS_RQ_DISPATCHED);
RQ_SET_STATE(rq, AS_RQ_REMOVED);
if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
atomic_dec(&RQ_IOC(rq)->aic->nr_dispatched);
}
static void as_deactivate_request(struct request_queue *q, struct request *rq)
{
WARN_ON(RQ_STATE(rq) != AS_RQ_REMOVED);
RQ_SET_STATE(rq, AS_RQ_DISPATCHED);
if (RQ_IOC(rq) && RQ_IOC(rq)->aic)
atomic_inc(&RQ_IOC(rq)->aic->nr_dispatched);
}
/*
* as_queue_empty tells us if there are requests left in the device. It may
* not be the case that a driver can get the next request even if the queue
* is not empty - it is used in the block layer to check for plugging and
* merging opportunities
*/
static int as_queue_empty(struct request_queue *q)
{
struct as_data *ad = q->elevator->elevator_data;
return list_empty(&ad->fifo_list[REQ_ASYNC])
&& list_empty(&ad->fifo_list[REQ_SYNC]);
}
static int
as_merge(struct request_queue *q, struct request **req, struct bio *bio)
{
struct as_data *ad = q->elevator->elevator_data;
sector_t rb_key = bio->bi_sector + bio_sectors(bio);
struct request *__rq;
/*
* check for front merge
*/
__rq = elv_rb_find(&ad->sort_list[bio_data_dir(bio)], rb_key);
if (__rq && elv_rq_merge_ok(__rq, bio)) {
*req = __rq;
return ELEVATOR_FRONT_MERGE;
}
return ELEVATOR_NO_MERGE;
}
static void as_merged_request(struct request_queue *q, struct request *req,
int type)
{
struct as_data *ad = q->elevator->elevator_data;
/*
* if the merge was a front merge, we need to reposition request
*/
if (type == ELEVATOR_FRONT_MERGE) {
as_del_rq_rb(ad, req);
as_add_rq_rb(ad, req);
/*
* Note! At this stage of this and the next function, our next
* request may not be optimal - eg the request may have "grown"
* behind the disk head. We currently don't bother adjusting.
*/
}
}
static void as_merged_requests(struct request_queue *q, struct request *req,
struct request *next)
{
/*
* if next expires before rq, assign its expire time to arq
* and move into next position (next will be deleted) in fifo
*/
if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
list_move(&req->queuelist, &next->queuelist);
rq_set_fifo_time(req, rq_fifo_time(next));
}
}
/*
* kill knowledge of next, this one is a goner
*/
as_remove_queued_request(q, next);
as_put_io_context(next);
RQ_SET_STATE(next, AS_RQ_MERGED);
}
/*
* This is executed in a "deferred" process context, by kblockd. It calls the
* driver's request_fn so the driver can submit that request.
*
* IMPORTANT! This guy will reenter the elevator, so set up all queue global
* state before calling, and don't rely on any state over calls.
*
* FIXME! dispatch queue is not a queue at all!
*/
static void as_work_handler(struct work_struct *work)
{
struct as_data *ad = container_of(work, struct as_data, antic_work);
struct request_queue *q = ad->q;
unsigned long flags;
spin_lock_irqsave(q->queue_lock, flags);
blk_start_queueing(q);
spin_unlock_irqrestore(q->queue_lock, flags);
}
static int as_may_queue(struct request_queue *q, int rw)
{
int ret = ELV_MQUEUE_MAY;
struct as_data *ad = q->elevator->elevator_data;
struct io_context *ioc;
if (ad->antic_status == ANTIC_WAIT_REQ ||
ad->antic_status == ANTIC_WAIT_NEXT) {
ioc = as_get_io_context(q->node);
if (ad->io_context == ioc)
ret = ELV_MQUEUE_MUST;
put_io_context(ioc);
}
return ret;
}
static void as_exit_queue(elevator_t *e)
{
struct as_data *ad = e->elevator_data;
del_timer_sync(&ad->antic_timer);
kblockd_flush_work(&ad->antic_work);
BUG_ON(!list_empty(&ad->fifo_list[REQ_SYNC]));
BUG_ON(!list_empty(&ad->fifo_list[REQ_ASYNC]));
put_io_context(ad->io_context);
kfree(ad);
}
/*
* initialize elevator private data (as_data).
*/
static void *as_init_queue(struct request_queue *q)
{
struct as_data *ad;
ad = kmalloc_node(sizeof(*ad), GFP_KERNEL | __GFP_ZERO, q->node);
if (!ad)
return NULL;
ad->q = q; /* Identify what queue the data belongs to */
/* anticipatory scheduling helpers */
ad->antic_timer.function = as_antic_timeout;
ad->antic_timer.data = (unsigned long)q;
init_timer(&ad->antic_timer);
INIT_WORK(&ad->antic_work, as_work_handler);
INIT_LIST_HEAD(&ad->fifo_list[REQ_SYNC]);
INIT_LIST_HEAD(&ad->fifo_list[REQ_ASYNC]);
ad->sort_list[REQ_SYNC] = RB_ROOT;
ad->sort_list[REQ_ASYNC] = RB_ROOT;
ad->fifo_expire[REQ_SYNC] = default_read_expire;
ad->fifo_expire[REQ_ASYNC] = default_write_expire;
ad->antic_expire = default_antic_expire;
ad->batch_expire[REQ_SYNC] = default_read_batch_expire;
ad->batch_expire[REQ_ASYNC] = default_write_batch_expire;
ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC];
ad->write_batch_count = ad->batch_expire[REQ_ASYNC] / 10;
if (ad->write_batch_count < 2)
ad->write_batch_count = 2;
return ad;
}
/*
* sysfs parts below
*/
static ssize_t
as_var_show(unsigned int var, char *page)
{
return sprintf(page, "%d\n", var);
}
static ssize_t
as_var_store(unsigned long *var, const char *page, size_t count)
{
char *p = (char *) page;
*var = simple_strtoul(p, &p, 10);
return count;
}
static ssize_t est_time_show(elevator_t *e, char *page)
{
struct as_data *ad = e->elevator_data;
int pos = 0;
pos += sprintf(page+pos, "%lu %% exit probability\n",
100*ad->exit_prob/256);
pos += sprintf(page+pos, "%lu %% probability of exiting without a "
"cooperating process submitting IO\n",
100*ad->exit_no_coop/256);
pos += sprintf(page+pos, "%lu ms new thinktime\n", ad->new_ttime_mean);
pos += sprintf(page+pos, "%llu sectors new seek distance\n",
(unsigned long long)ad->new_seek_mean);
return pos;
}
#define SHOW_FUNCTION(__FUNC, __VAR) \
static ssize_t __FUNC(elevator_t *e, char *page) \
{ \
struct as_data *ad = e->elevator_data; \
return as_var_show(jiffies_to_msecs((__VAR)), (page)); \
}
SHOW_FUNCTION(as_read_expire_show, ad->fifo_expire[REQ_SYNC]);
SHOW_FUNCTION(as_write_expire_show, ad->fifo_expire[REQ_ASYNC]);
SHOW_FUNCTION(as_antic_expire_show, ad->antic_expire);
SHOW_FUNCTION(as_read_batch_expire_show, ad->batch_expire[REQ_SYNC]);
SHOW_FUNCTION(as_write_batch_expire_show, ad->batch_expire[REQ_ASYNC]);
#undef SHOW_FUNCTION
#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
static ssize_t __FUNC(elevator_t *e, const char *page, size_t count) \
{ \
struct as_data *ad = e->elevator_data; \
int ret = as_var_store(__PTR, (page), count); \
if (*(__PTR) < (MIN)) \
*(__PTR) = (MIN); \
else if (*(__PTR) > (MAX)) \
*(__PTR) = (MAX); \
*(__PTR) = msecs_to_jiffies(*(__PTR)); \
return ret; \
}
STORE_FUNCTION(as_read_expire_store, &ad->fifo_expire[REQ_SYNC], 0, INT_MAX);
STORE_FUNCTION(as_write_expire_store, &ad->fifo_expire[REQ_ASYNC], 0, INT_MAX);
STORE_FUNCTION(as_antic_expire_store, &ad->antic_expire, 0, INT_MAX);
STORE_FUNCTION(as_read_batch_expire_store,
&ad->batch_expire[REQ_SYNC], 0, INT_MAX);
STORE_FUNCTION(as_write_batch_expire_store,
&ad->batch_expire[REQ_ASYNC], 0, INT_MAX);
#undef STORE_FUNCTION
#define AS_ATTR(name) \
__ATTR(name, S_IRUGO|S_IWUSR, as_##name##_show, as_##name##_store)
static struct elv_fs_entry as_attrs[] = {
__ATTR_RO(est_time),
AS_ATTR(read_expire),
AS_ATTR(write_expire),
AS_ATTR(antic_expire),
AS_ATTR(read_batch_expire),
AS_ATTR(write_batch_expire),
__ATTR_NULL
};
static struct elevator_type iosched_as = {
.ops = {
.elevator_merge_fn = as_merge,
.elevator_merged_fn = as_merged_request,
.elevator_merge_req_fn = as_merged_requests,
.elevator_dispatch_fn = as_dispatch_request,
.elevator_add_req_fn = as_add_request,
.elevator_activate_req_fn = as_activate_request,
.elevator_deactivate_req_fn = as_deactivate_request,
.elevator_queue_empty_fn = as_queue_empty,
.elevator_completed_req_fn = as_completed_request,
.elevator_former_req_fn = elv_rb_former_request,
.elevator_latter_req_fn = elv_rb_latter_request,
.elevator_may_queue_fn = as_may_queue,
.elevator_init_fn = as_init_queue,
.elevator_exit_fn = as_exit_queue,
.trim = as_trim,
},
.elevator_attrs = as_attrs,
.elevator_name = "anticipatory",
.elevator_owner = THIS_MODULE,
};
static int __init as_init(void)
{
elv_register(&iosched_as);
return 0;
}
static void __exit as_exit(void)
{
DECLARE_COMPLETION_ONSTACK(all_gone);
elv_unregister(&iosched_as);
ioc_gone = &all_gone;
/* ioc_gone's update must be visible before reading ioc_count */
smp_wmb();
if (elv_ioc_count_read(ioc_count))
wait_for_completion(&all_gone);
synchronize_rcu();
}
module_init(as_init);
module_exit(as_exit);
MODULE_AUTHOR("Nick Piggin");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("anticipatory IO scheduler");