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blkcg: remove blkio_group->stats_lock
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With recent plug merge updates, all non-percpu stat updates happen
under queue_lock making stats_lock unnecessary to synchronize stat
updates.  The only synchronization necessary is stat reading, which
can be done using u64_stats_sync instead.

This patch removes blkio_group->stats_lock and adds
blkio_group_stats->syncp for reader synchronization.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Tejun Heo authored and Jens Axboe committed Mar 20, 2012
1 parent c4c76a0 commit edf1b87
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Showing 2 changed files with 103 additions and 109 deletions.
209 changes: 102 additions & 107 deletions block/blk-cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -156,7 +156,7 @@ static inline void blkio_update_group_iops(struct blkio_group *blkg,

/*
* Add to the appropriate stat variable depending on the request type.
* This should be called with the blkg->stats_lock held.
* This should be called with queue_lock held.
*/
static void blkio_add_stat(uint64_t *stat, uint64_t add, bool direction,
bool sync)
Expand All @@ -174,7 +174,7 @@ static void blkio_add_stat(uint64_t *stat, uint64_t add, bool direction,
/*
* Decrements the appropriate stat variable if non-zero depending on the
* request type. Panics on value being zero.
* This should be called with the blkg->stats_lock held.
* This should be called with the queue_lock held.
*/
static void blkio_check_and_dec_stat(uint64_t *stat, bool direction, bool sync)
{
Expand All @@ -195,7 +195,7 @@ static void blkio_check_and_dec_stat(uint64_t *stat, bool direction, bool sync)
}

#ifdef CONFIG_DEBUG_BLK_CGROUP
/* This should be called with the blkg->stats_lock held. */
/* This should be called with the queue_lock held. */
static void blkio_set_start_group_wait_time(struct blkio_group *blkg,
struct blkio_policy_type *pol,
struct blkio_group *curr_blkg)
Expand All @@ -210,7 +210,7 @@ static void blkio_set_start_group_wait_time(struct blkio_group *blkg,
blkio_mark_blkg_waiting(&pd->stats);
}

/* This should be called with the blkg->stats_lock held. */
/* This should be called with the queue_lock held. */
static void blkio_update_group_wait_time(struct blkio_group_stats *stats)
{
unsigned long long now;
Expand All @@ -224,7 +224,7 @@ static void blkio_update_group_wait_time(struct blkio_group_stats *stats)
blkio_clear_blkg_waiting(stats);
}

/* This should be called with the blkg->stats_lock held. */
/* This should be called with the queue_lock held. */
static void blkio_end_empty_time(struct blkio_group_stats *stats)
{
unsigned long long now;
Expand All @@ -241,84 +241,74 @@ static void blkio_end_empty_time(struct blkio_group_stats *stats)
void blkiocg_update_set_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

spin_lock_irqsave(&blkg->stats_lock, flags);
BUG_ON(blkio_blkg_idling(&pd->stats));
pd->stats.start_idle_time = sched_clock();
blkio_mark_blkg_idling(&pd->stats);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
lockdep_assert_held(blkg->q->queue_lock);
BUG_ON(blkio_blkg_idling(stats));

stats->start_idle_time = sched_clock();
blkio_mark_blkg_idling(stats);
}
EXPORT_SYMBOL_GPL(blkiocg_update_set_idle_time_stats);

void blkiocg_update_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
unsigned long long now;
struct blkio_group_stats *stats;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

lockdep_assert_held(blkg->q->queue_lock);

spin_lock_irqsave(&blkg->stats_lock, flags);
stats = &pd->stats;
if (blkio_blkg_idling(stats)) {
now = sched_clock();
if (time_after64(now, stats->start_idle_time))
unsigned long long now = sched_clock();

if (time_after64(now, stats->start_idle_time)) {
u64_stats_update_begin(&stats->syncp);
stats->idle_time += now - stats->start_idle_time;
u64_stats_update_end(&stats->syncp);
}
blkio_clear_blkg_idling(stats);
}
spin_unlock_irqrestore(&blkg->stats_lock, flags);
}
EXPORT_SYMBOL_GPL(blkiocg_update_idle_time_stats);

void blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

spin_lock_irqsave(&blkg->stats_lock, flags);
stats = &pd->stats;
lockdep_assert_held(blkg->q->queue_lock);

u64_stats_update_begin(&stats->syncp);
stats->avg_queue_size_sum +=
stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_READ] +
stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_WRITE];
stats->avg_queue_size_samples++;
blkio_update_group_wait_time(stats);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
u64_stats_update_end(&stats->syncp);
}
EXPORT_SYMBOL_GPL(blkiocg_update_avg_queue_size_stats);

void blkiocg_set_start_empty_time(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

spin_lock_irqsave(&blkg->stats_lock, flags);
stats = &pd->stats;
lockdep_assert_held(blkg->q->queue_lock);

if (stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_READ] ||
stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_WRITE]) {
spin_unlock_irqrestore(&blkg->stats_lock, flags);
stats->stat_arr[BLKIO_STAT_QUEUED][BLKIO_STAT_WRITE])
return;
}

/*
* group is already marked empty. This can happen if cfqq got new
* request in parent group and moved to this group while being added
* to service tree. Just ignore the event and move on.
*/
if(blkio_blkg_empty(stats)) {
spin_unlock_irqrestore(&blkg->stats_lock, flags);
if (blkio_blkg_empty(stats))
return;
}

stats->start_empty_time = sched_clock();
blkio_mark_blkg_empty(stats);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
}
EXPORT_SYMBOL_GPL(blkiocg_set_start_empty_time);

Expand All @@ -328,6 +318,8 @@ void blkiocg_update_dequeue_stats(struct blkio_group *blkg,
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];

lockdep_assert_held(blkg->q->queue_lock);

pd->stats.dequeue += dequeue;
}
EXPORT_SYMBOL_GPL(blkiocg_update_dequeue_stats);
Expand All @@ -343,29 +335,31 @@ void blkiocg_update_io_add_stats(struct blkio_group *blkg,
struct blkio_group *curr_blkg, bool direction,
bool sync)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

lockdep_assert_held(blkg->q->queue_lock);

u64_stats_update_begin(&stats->syncp);
blkio_add_stat(stats->stat_arr[BLKIO_STAT_QUEUED], 1, direction, sync);
blkio_end_empty_time(stats);
u64_stats_update_end(&stats->syncp);

spin_lock_irqsave(&blkg->stats_lock, flags);
blkio_add_stat(pd->stats.stat_arr[BLKIO_STAT_QUEUED], 1, direction,
sync);
blkio_end_empty_time(&pd->stats);
blkio_set_start_group_wait_time(blkg, pol, curr_blkg);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_add_stats);

void blkiocg_update_io_remove_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol,
bool direction, bool sync)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

spin_lock_irqsave(&blkg->stats_lock, flags);
blkio_check_and_dec_stat(pd->stats.stat_arr[BLKIO_STAT_QUEUED],
direction, sync);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
lockdep_assert_held(blkg->q->queue_lock);

u64_stats_update_begin(&stats->syncp);
blkio_check_and_dec_stat(stats->stat_arr[BLKIO_STAT_QUEUED], direction,
sync);
u64_stats_update_end(&stats->syncp);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_remove_stats);

Expand All @@ -374,15 +368,16 @@ void blkiocg_update_timeslice_used(struct blkio_group *blkg,
unsigned long time,
unsigned long unaccounted_time)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

lockdep_assert_held(blkg->q->queue_lock);

spin_lock_irqsave(&blkg->stats_lock, flags);
pd->stats.time += time;
u64_stats_update_begin(&stats->syncp);
stats->time += time;
#ifdef CONFIG_DEBUG_BLK_CGROUP
pd->stats.unaccounted_time += unaccounted_time;
stats->unaccounted_time += unaccounted_time;
#endif
spin_unlock_irqrestore(&blkg->stats_lock, flags);
u64_stats_update_end(&stats->syncp);
}
EXPORT_SYMBOL_GPL(blkiocg_update_timeslice_used);

Expand Down Expand Up @@ -428,20 +423,19 @@ void blkiocg_update_completion_stats(struct blkio_group *blkg,
uint64_t io_start_time, bool direction,
bool sync)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
struct blkio_group_stats *stats;
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
unsigned long long now = sched_clock();

spin_lock_irqsave(&blkg->stats_lock, flags);
stats = &pd->stats;
lockdep_assert_held(blkg->q->queue_lock);

u64_stats_update_begin(&stats->syncp);
if (time_after64(now, io_start_time))
blkio_add_stat(stats->stat_arr[BLKIO_STAT_SERVICE_TIME],
now - io_start_time, direction, sync);
if (time_after64(io_start_time, start_time))
blkio_add_stat(stats->stat_arr[BLKIO_STAT_WAIT_TIME],
io_start_time - start_time, direction, sync);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
u64_stats_update_end(&stats->syncp);
}
EXPORT_SYMBOL_GPL(blkiocg_update_completion_stats);

Expand All @@ -450,14 +444,13 @@ void blkiocg_update_io_merged_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol,
bool direction, bool sync)
{
struct blkg_policy_data *pd = blkg->pd[pol->plid];
struct blkio_group_stats *stats;
unsigned long flags;
struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;

spin_lock_irqsave(&blkg->stats_lock, flags);
stats = &pd->stats;
lockdep_assert_held(blkg->q->queue_lock);

u64_stats_update_begin(&stats->syncp);
blkio_add_stat(stats->stat_arr[BLKIO_STAT_MERGED], 1, direction, sync);
spin_unlock_irqrestore(&blkg->stats_lock, flags);
u64_stats_update_end(&stats->syncp);
}
EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);

Expand Down Expand Up @@ -558,7 +551,6 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
if (!blkg)
return NULL;

spin_lock_init(&blkg->stats_lock);
blkg->q = q;
INIT_LIST_HEAD(&blkg->q_node);
INIT_LIST_HEAD(&blkg->alloc_node);
Expand Down Expand Up @@ -929,58 +921,64 @@ static uint64_t blkio_get_stat_cpu(struct blkio_group *blkg, int plid,
return disk_total;
}

/* This should be called with blkg->stats_lock held */
static uint64_t blkio_get_stat(struct blkio_group *blkg, int plid,
struct cgroup_map_cb *cb, const char *dname,
enum stat_type type)
{
struct blkio_group_stats *stats = &blkg->pd[plid]->stats;
uint64_t v = 0, disk_total = 0;
char key_str[MAX_KEY_LEN];
unsigned int sync_start;
int st;

if (type >= BLKIO_STAT_ARR_NR) {
switch (type) {
case BLKIO_STAT_TIME:
v = stats->time;
break;
do {
sync_start = u64_stats_fetch_begin(&stats->syncp);
switch (type) {
case BLKIO_STAT_TIME:
v = stats->time;
break;
#ifdef CONFIG_DEBUG_BLK_CGROUP
case BLKIO_STAT_UNACCOUNTED_TIME:
v = stats->unaccounted_time;
break;
case BLKIO_STAT_AVG_QUEUE_SIZE: {
uint64_t samples = stats->avg_queue_size_samples;
case BLKIO_STAT_UNACCOUNTED_TIME:
v = stats->unaccounted_time;
break;
case BLKIO_STAT_AVG_QUEUE_SIZE: {
uint64_t samples = stats->avg_queue_size_samples;

if (samples) {
v = stats->avg_queue_size_sum;
do_div(v, samples);
if (samples) {
v = stats->avg_queue_size_sum;
do_div(v, samples);
}
break;
}
break;
}
case BLKIO_STAT_IDLE_TIME:
v = stats->idle_time;
break;
case BLKIO_STAT_EMPTY_TIME:
v = stats->empty_time;
break;
case BLKIO_STAT_DEQUEUE:
v = stats->dequeue;
break;
case BLKIO_STAT_GROUP_WAIT_TIME:
v = stats->group_wait_time;
break;
case BLKIO_STAT_IDLE_TIME:
v = stats->idle_time;
break;
case BLKIO_STAT_EMPTY_TIME:
v = stats->empty_time;
break;
case BLKIO_STAT_DEQUEUE:
v = stats->dequeue;
break;
case BLKIO_STAT_GROUP_WAIT_TIME:
v = stats->group_wait_time;
break;
#endif
default:
WARN_ON_ONCE(1);
}
default:
WARN_ON_ONCE(1);
}
} while (u64_stats_fetch_retry(&stats->syncp, sync_start));

blkio_get_key_name(0, dname, key_str, MAX_KEY_LEN, true);
cb->fill(cb, key_str, v);
return v;
}

for (st = BLKIO_STAT_READ; st < BLKIO_STAT_TOTAL; st++) {
v = stats->stat_arr[type][st];
do {
sync_start = u64_stats_fetch_begin(&stats->syncp);
v = stats->stat_arr[type][st];
} while (u64_stats_fetch_retry(&stats->syncp, sync_start));

blkio_get_key_name(st, dname, key_str, MAX_KEY_LEN, false);
cb->fill(cb, key_str, v);
Expand Down Expand Up @@ -1250,15 +1248,12 @@ static int blkio_read_blkg_stats(struct blkio_cgroup *blkcg,

if (!dname)
continue;
if (pcpu) {
if (pcpu)
cgroup_total += blkio_get_stat_cpu(blkg, plid,
cb, dname, type);
} else {
spin_lock(&blkg->stats_lock);
else
cgroup_total += blkio_get_stat(blkg, plid,
cb, dname, type);
spin_unlock(&blkg->stats_lock);
}
}
if (show_total)
cb->fill(cb, "Total", cgroup_total);
Expand Down
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