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[PATCH] cfq-iosched: slice expiry fixups
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During testing of SLES10, we encountered a hang in the CFQ io scheduler.
Turns out the deferred slice expiry logic is buggy, so remove that for
now.  We could be left with an idle queue that would never wake up.  So
kill that logic, always expire immediately.  Also fix a potential timer
race condition.

Patch looks bigger than it is, because it moves a function.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Jens Axboe authored and Linus Torvalds committed Feb 28, 2006
1 parent a8b76b4 commit 7b14e3b
Showing 1 changed file with 60 additions and 91 deletions.
151 changes: 60 additions & 91 deletions block/cfq-iosched.c
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Original file line number Diff line number Diff line change
Expand Up @@ -239,7 +239,6 @@ enum cfqq_state_flags {
CFQ_CFQQ_FLAG_fifo_expire,
CFQ_CFQQ_FLAG_idle_window,
CFQ_CFQQ_FLAG_prio_changed,
CFQ_CFQQ_FLAG_expired,
};

#define CFQ_CFQQ_FNS(name) \
Expand All @@ -264,7 +263,6 @@ CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(expired);
#undef CFQ_CFQQ_FNS

enum cfq_rq_state_flags {
Expand Down Expand Up @@ -336,7 +334,7 @@ static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
*/
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
if (!cfqd->rq_in_driver && cfqd->busy_queues)
if (cfqd->busy_queues)
kblockd_schedule_work(&cfqd->unplug_work);
}

Expand Down Expand Up @@ -736,12 +734,62 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfqq->slice_left = 0;
cfq_clear_cfqq_must_alloc_slice(cfqq);
cfq_clear_cfqq_fifo_expire(cfqq);
cfq_clear_cfqq_expired(cfqq);
}

cfqd->active_queue = cfqq;
}

/*
* current cfqq expired its slice (or was too idle), select new one
*/
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
int preempted)
{
unsigned long now = jiffies;

if (cfq_cfqq_wait_request(cfqq))
del_timer(&cfqd->idle_slice_timer);

if (!preempted && !cfq_cfqq_dispatched(cfqq)) {
cfqq->service_last = now;
cfq_schedule_dispatch(cfqd);
}

cfq_clear_cfqq_must_dispatch(cfqq);
cfq_clear_cfqq_wait_request(cfqq);

/*
* store what was left of this slice, if the queue idled out
* or was preempted
*/
if (time_after(cfqq->slice_end, now))
cfqq->slice_left = cfqq->slice_end - now;
else
cfqq->slice_left = 0;

if (cfq_cfqq_on_rr(cfqq))
cfq_resort_rr_list(cfqq, preempted);

if (cfqq == cfqd->active_queue)
cfqd->active_queue = NULL;

if (cfqd->active_cic) {
put_io_context(cfqd->active_cic->ioc);
cfqd->active_cic = NULL;
}

cfqd->dispatch_slice = 0;
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
{
struct cfq_queue *cfqq = cfqd->active_queue;

if (cfqq)
__cfq_slice_expired(cfqd, cfqq, preempted);
}

/*
* 0
* 0,1
Expand Down Expand Up @@ -801,16 +849,7 @@ static int cfq_get_next_prio_level(struct cfq_data *cfqd)

static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq;

/*
* if current queue is expired but not done with its requests yet,
* wait for that to happen
*/
if ((cfqq = cfqd->active_queue) != NULL) {
if (cfq_cfqq_expired(cfqq) && cfq_cfqq_dispatched(cfqq))
return NULL;
}
struct cfq_queue *cfqq = NULL;

/*
* if current list is non-empty, grab first entry. if it is empty,
Expand All @@ -837,66 +876,11 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
return cfqq;
}

/*
* current cfqq expired its slice (or was too idle), select new one
*/
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
int preempted)
{
unsigned long now = jiffies;

if (cfq_cfqq_wait_request(cfqq))
del_timer(&cfqd->idle_slice_timer);

if (!preempted && !cfq_cfqq_dispatched(cfqq))
cfqq->service_last = now;

cfq_clear_cfqq_must_dispatch(cfqq);
cfq_clear_cfqq_wait_request(cfqq);

/*
* store what was left of this slice, if the queue idled out
* or was preempted
*/
if (time_after(cfqq->slice_end, now))
cfqq->slice_left = cfqq->slice_end - now;
else
cfqq->slice_left = 0;

if (cfq_cfqq_on_rr(cfqq))
cfq_resort_rr_list(cfqq, preempted);

if (cfqq == cfqd->active_queue)
cfqd->active_queue = NULL;

if (cfqd->active_cic) {
put_io_context(cfqd->active_cic->ioc);
cfqd->active_cic = NULL;
}

cfqd->dispatch_slice = 0;
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
{
struct cfq_queue *cfqq = cfqd->active_queue;

if (cfqq) {
/*
* use deferred expiry, if there are requests in progress as
* not to disturb the slice of the next queue
*/
if (cfq_cfqq_dispatched(cfqq))
cfq_mark_cfqq_expired(cfqq);
else
__cfq_slice_expired(cfqd, cfqq, preempted);
}
}

static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)

{
unsigned long sl;

WARN_ON(!RB_EMPTY(&cfqq->sort_list));
WARN_ON(cfqq != cfqd->active_queue);

Expand All @@ -916,13 +900,8 @@ static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfq_mark_cfqq_must_dispatch(cfqq);
cfq_mark_cfqq_wait_request(cfqq);

if (!timer_pending(&cfqd->idle_slice_timer)) {
unsigned long slice_left = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);

cfqd->idle_slice_timer.expires = jiffies + slice_left;
add_timer(&cfqd->idle_slice_timer);
}

sl = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);
mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
return 1;
}

Expand Down Expand Up @@ -1006,9 +985,6 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
if (!cfqq)
goto new_queue;

if (cfq_cfqq_expired(cfqq))
goto new_queue;

/*
* slice has expired
*/
Expand Down Expand Up @@ -1181,10 +1157,8 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
BUG_ON(cfq_cfqq_on_rr(cfqq));

if (unlikely(cfqd->active_queue == cfqq)) {
if (unlikely(cfqd->active_queue == cfqq))
__cfq_slice_expired(cfqd, cfqq, 0);
cfq_schedule_dispatch(cfqd);
}

cfq_put_cfqd(cfqq->cfqd);

Expand Down Expand Up @@ -1245,10 +1219,8 @@ static void cfq_exit_single_io_context(struct cfq_io_context *cic)

spin_lock(q->queue_lock);

if (unlikely(cic->cfqq == cfqd->active_queue)) {
if (unlikely(cic->cfqq == cfqd->active_queue))
__cfq_slice_expired(cfqd, cic->cfqq, 0);
cfq_schedule_dispatch(cfqd);
}

cfq_put_queue(cic->cfqq);
cic->cfqq = NULL;
Expand Down Expand Up @@ -1715,10 +1687,7 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
cfqq->service_last = now;
cfq_resort_rr_list(cfqq, 0);
}
if (cfq_cfqq_expired(cfqq)) {
__cfq_slice_expired(cfqd, cfqq, 0);
cfq_schedule_dispatch(cfqd);
}
cfq_schedule_dispatch(cfqd);
}

if (cfq_crq_is_sync(crq))
Expand Down

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