[PATCH 07/10] blkcg: make blkcg_[rw]stat per-cpu

Tejun Heo
2015-07-12T18:02:09Z

blkcg_[rw]stat are used as stat counters for blkcg policies. It isn't
per-cpu by itself and blk-throttle makes it per-cpu by wrapping around
it. This patch makes blkcg_[rw]stat per-cpu and drop the ad-hoc
per-cpu wrapping in blk-throttle.

* blkg_[rw]stat->cnt is replaced with cpu_cnt which is struct
percpu_counter. This makes syncp unnecessary as remote accesses are
handled by percpu_counter itself.

* blkg_[rw]stat_init() can now fail due to percpu allocation failure
and thus are updated to return int.

* percpu_counters need explicit freeing. blkg_[rw]stat_exit() added.

* As blkg_rwstat->cpu_cnt[] can't be read directly anymore, reading
and summing results are stored in ->aux_cnt[] instead.

* Custom per-cpu stat implementation in blk-throttle is removed.

This makes all blkcg stat counters per-cpu without complicating policy
implmentations.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
block/blk-cgroup.c | 10 ++--
block/blk-throttle.c | 89 +++++++++++----------------------
block/cfq-iosched.c | 70 +++++++++++++++++++-------
include/linux/blk-cgroup.h | 120 +++++++++++++++++++++++++--------------------
4 files changed, 153 insertions(+), 136 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 55cfa11..caabda1 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -539,9 +539,10 @@ u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,

for (i = 0; i < BLKG_RWSTAT_NR; i++)
seq_printf(sf, "%s %s %llu\n", dname, rwstr[i],
- (unsigned long long)rwstat->cnt[i]);
+ (unsigned long long)atomic64_read(&rwstat->aux_cnt[i]));

- v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
+ v = atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_READ]) +
+ atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_WRITE]);
seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
return v;
}
@@ -643,8 +644,9 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkg_policy_data *pd,
tmp = blkg_rwstat_read(rwstat);

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- sum.cnt[i] += tmp.cnt[i] +
- atomic64_read(&rwstat->aux_cnt[i]);
+ atomic64_add(atomic64_read(&tmp.aux_cnt[i]) +
+ atomic64_read(&rwstat->aux_cnt[i]),
+ &sum.aux_cnt[i]);
}
rcu_read_unlock();

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 29c22ed..c0b2263 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -83,14 +83,6 @@ enum tg_state_flags {

#define rb_entry_tg(node) rb_entry((node), struct throtl_grp, rb_node)

-/* Per-cpu group stats */
-struct tg_stats_cpu {
- /* total bytes transferred */
- struct blkg_rwstat service_bytes;
- /* total IOs serviced, post merge */
- struct blkg_rwstat serviced;
-};
-
struct throtl_grp {
/* must be the first member */
struct blkg_policy_data pd;
@@ -142,8 +134,10 @@ struct throtl_grp {
unsigned long slice_start[2];
unsigned long slice_end[2];

- /* Per cpu stats pointer */
- struct tg_stats_cpu __percpu *stats_cpu;
+ /* total bytes transferred */
+ struct blkg_rwstat service_bytes;
+ /* total IOs serviced, post merge */
+ struct blkg_rwstat serviced;
};

struct throtl_data
@@ -337,17 +331,15 @@ static void throtl_service_queue_init(struct throtl_service_queue *sq)
static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
{
struct throtl_grp *tg;
- int rw, cpu;
+ int rw;

tg = kzalloc_node(sizeof(*tg), gfp, node);
if (!tg)
- return NULL;
+ goto err;

- tg->stats_cpu = alloc_percpu_gfp(struct tg_stats_cpu, gfp);
- if (!tg->stats_cpu) {
- kfree(tg);
- return NULL;
- }
+ if (blkg_rwstat_init(&tg->service_bytes, gfp) ||
+ blkg_rwstat_init(&tg->serviced, gfp))
+ goto err_free_tg;

throtl_service_queue_init(&tg->service_queue);

@@ -362,14 +354,14 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
tg->iops[READ] = -1;
tg->iops[WRITE] = -1;

- for_each_possible_cpu(cpu) {
- struct tg_stats_cpu *stats_cpu = per_cpu_ptr(tg->stats_cpu, cpu);
-
- blkg_rwstat_init(&stats_cpu->service_bytes);
- blkg_rwstat_init(&stats_cpu->serviced);
- }
-
return &tg->pd;
+
+err_free_tg:
+ blkg_rwstat_exit(&tg->serviced);
+ blkg_rwstat_exit(&tg->service_bytes);
+ kfree(tg);
+err:
+ return NULL;
}

static void throtl_pd_init(struct blkg_policy_data *pd)
@@ -427,21 +419,17 @@ static void throtl_pd_free(struct blkg_policy_data *pd)
struct throtl_grp *tg = pd_to_tg(pd);

del_timer_sync(&tg->service_queue.pending_timer);
- free_percpu(tg->stats_cpu);
+ blkg_rwstat_exit(&tg->serviced);
+ blkg_rwstat_exit(&tg->service_bytes);
kfree(tg);
}

static void throtl_pd_reset_stats(struct blkg_policy_data *pd)
{
struct throtl_grp *tg = pd_to_tg(pd);
- int cpu;

- for_each_possible_cpu(cpu) {
- struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
-
- blkg_rwstat_reset(&sc->service_bytes);
- blkg_rwstat_reset(&sc->serviced);
- }
+ blkg_rwstat_reset(&tg->service_bytes);
+ blkg_rwstat_reset(&tg->serviced);
}

static struct throtl_grp *
@@ -855,7 +843,6 @@ static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
int rw)
{
struct throtl_grp *tg = blkg_to_tg(blkg);
- struct tg_stats_cpu *stats_cpu;
unsigned long flags;

/*
@@ -865,10 +852,8 @@ static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
*/
local_irq_save(flags);

- stats_cpu = this_cpu_ptr(tg->stats_cpu);
-
- blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
- blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);
+ blkg_rwstat_add(&tg->serviced, rw, 1);
+ blkg_rwstat_add(&tg->service_bytes, rw, bytes);

local_irq_restore(flags);
}
@@ -1176,27 +1161,9 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work)
}
}

-static u64 tg_prfill_cpu_rwstat(struct seq_file *sf,
- struct blkg_policy_data *pd, int off)
-{
- struct throtl_grp *tg = pd_to_tg(pd);
- struct blkg_rwstat rwstat = { }, tmp;
- int i, cpu;
-
- for_each_possible_cpu(cpu) {
- struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
-
- tmp = blkg_rwstat_read((void *)sc + off);
- for (i = 0; i < BLKG_RWSTAT_NR; i++)
- rwstat.cnt[i] += tmp.cnt[i];
- }
-
- return __blkg_prfill_rwstat(sf, pd, &rwstat);
-}
-
-static int tg_print_cpu_rwstat(struct seq_file *sf, void *v)
+static int tg_print_rwstat(struct seq_file *sf, void *v)
{
- blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_cpu_rwstat,
+ blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), blkg_prfill_rwstat,
&blkcg_policy_throtl, seq_cft(sf)->private, true);
return 0;
}
@@ -1337,13 +1304,13 @@ static struct cftype throtl_files[] = {
},
{
.name = "throttle.io_service_bytes",
- .private = offsetof(struct tg_stats_cpu, service_bytes),
- .seq_show = tg_print_cpu_rwstat,
+ .private = offsetof(struct throtl_grp, service_bytes),
+ .seq_show = tg_print_rwstat,
},
{
.name = "throttle.io_serviced",
- .private = offsetof(struct tg_stats_cpu, serviced),
- .seq_show = tg_print_cpu_rwstat,
+ .private = offsetof(struct throtl_grp, serviced),
+ .seq_show = tg_print_rwstat,
},
{ } /* terminate */
};
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 0440e7d..9a0d8e8 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1542,27 +1542,55 @@ static void cfq_init_cfqg_base(struct cfq_group *cfqg)
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
-static void cfqg_stats_init(struct cfqg_stats *stats)
+static void cfqg_stats_exit(struct cfqg_stats *stats)
{
- blkg_rwstat_init(&stats->service_bytes);
- blkg_rwstat_init(&stats->serviced);
- blkg_rwstat_init(&stats->merged);
- blkg_rwstat_init(&stats->service_time);
- blkg_rwstat_init(&stats->wait_time);
- blkg_rwstat_init(&stats->queued);
+ blkg_rwstat_exit(&stats->service_bytes);
+ blkg_rwstat_exit(&stats->serviced);
+ blkg_rwstat_exit(&stats->merged);
+ blkg_rwstat_exit(&stats->service_time);
+ blkg_rwstat_exit(&stats->wait_time);
+ blkg_rwstat_exit(&stats->queued);

- blkg_stat_init(&stats->sectors);
- blkg_stat_init(&stats->time);
+ blkg_stat_exit(&stats->sectors);
+ blkg_stat_exit(&stats->time);
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+ blkg_stat_exit(&stats->unaccounted_time);
+ blkg_stat_exit(&stats->avg_queue_size_sum);
+ blkg_stat_exit(&stats->avg_queue_size_samples);
+ blkg_stat_exit(&stats->dequeue);
+ blkg_stat_exit(&stats->group_wait_time);
+ blkg_stat_exit(&stats->idle_time);
+ blkg_stat_exit(&stats->empty_time);
+#endif
+}
+
+static int cfqg_stats_init(struct cfqg_stats *stats, gfp_t gfp)
+{
+ if (blkg_rwstat_init(&stats->service_bytes, gfp) ||
+ blkg_rwstat_init(&stats->serviced, gfp) ||
+ blkg_rwstat_init(&stats->merged, gfp) ||
+ blkg_rwstat_init(&stats->service_time, gfp) ||
+ blkg_rwstat_init(&stats->wait_time, gfp) ||
+ blkg_rwstat_init(&stats->queued, gfp) ||
+
+ blkg_stat_init(&stats->sectors, gfp) ||
+ blkg_stat_init(&stats->time, gfp))
+ goto err;

#ifdef CONFIG_DEBUG_BLK_CGROUP
- blkg_stat_init(&stats->unaccounted_time);
- blkg_stat_init(&stats->avg_queue_size_sum);
- blkg_stat_init(&stats->avg_queue_size_samples);
- blkg_stat_init(&stats->dequeue);
- blkg_stat_init(&stats->group_wait_time);
- blkg_stat_init(&stats->idle_time);
- blkg_stat_init(&stats->empty_time);
+ if (blkg_stat_init(&stats->unaccounted_time, gfp) ||
+ blkg_stat_init(&stats->avg_queue_size_sum, gfp) ||
+ blkg_stat_init(&stats->avg_queue_size_samples, gfp) ||
+ blkg_stat_init(&stats->dequeue, gfp) ||
+ blkg_stat_init(&stats->group_wait_time, gfp) ||
+ blkg_stat_init(&stats->idle_time, gfp) ||
+ blkg_stat_init(&stats->empty_time, gfp))
+ goto err;
#endif
+ return 0;
+err:
+ cfqg_stats_exit(stats);
+ return -ENOMEM;
}

static struct blkcg_policy_data *cfq_cpd_alloc(gfp_t gfp)
@@ -1602,7 +1630,10 @@ static struct blkg_policy_data *cfq_pd_alloc(gfp_t gfp, int node)
return NULL;

cfq_init_cfqg_base(cfqg);
- cfqg_stats_init(&cfqg->stats);
+ if (cfqg_stats_init(&cfqg->stats, gfp)) {
+ kfree(cfqg);
+ return NULL;
+ }

return &cfqg->pd;
}
@@ -1642,7 +1673,10 @@ static void cfq_pd_offline(struct blkg_policy_data *pd)

static void cfq_pd_free(struct blkg_policy_data *pd)
{
- return kfree(pd);
+ struct cfq_group *cfqg = pd_to_cfqg(pd);
+
+ cfqg_stats_exit(&cfqg->stats);
+ return kfree(cfqg);
}

static void cfq_pd_reset_stats(struct blkg_policy_data *pd)
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 44e45d2..ddbf580 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -14,12 +14,15 @@
*/

#include <linux/cgroup.h>
-#include <linux/u64_stats_sync.h>
+#include <linux/percpu_counter.h>
#include <linux/seq_file.h>
#include <linux/radix-tree.h>
#include <linux/blkdev.h>
#include <linux/atomic.h>

+/* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
+#define BLKG_STAT_CPU_BATCH (INT_MAX / 2)
+
/* Max limits for throttle policy */
#define THROTL_IOPS_MAX UINT_MAX

@@ -55,17 +58,16 @@ struct blkcg {

/*
* blkg_[rw]stat->aux_cnt is excluded for local stats but included for
- * recursive. Used to carry stats of dead children.
+ * recursive. Used to carry stats of dead children, and, for blkg_rwstat,
+ * to carry result values from read and sum operations.
*/
struct blkg_stat {
- struct u64_stats_sync syncp;
- uint64_t cnt;
+ struct percpu_counter cpu_cnt;
atomic64_t aux_cnt;
};

struct blkg_rwstat {
- struct u64_stats_sync syncp;
- uint64_t cnt[BLKG_RWSTAT_NR];
+ struct percpu_counter cpu_cnt[BLKG_RWSTAT_NR];
atomic64_t aux_cnt[BLKG_RWSTAT_NR];
};

@@ -486,10 +488,21 @@ struct request_list *__blk_queue_next_rl(struct request_list *rl,
#define blk_queue_for_each_rl(rl, q) \
for ((rl) = &(q)->root_rl; (rl); (rl) = __blk_queue_next_rl((rl), (q)))

-static inline void blkg_stat_init(struct blkg_stat *stat)
+static inline int blkg_stat_init(struct blkg_stat *stat, gfp_t gfp)
{
- u64_stats_init(&stat->syncp);
+ int ret;
+
+ ret = percpu_counter_init(&stat->cpu_cnt, 0, gfp);
+ if (ret)
+ return ret;
+
atomic64_set(&stat->aux_cnt, 0);
+ return 0;
+}
+
+static inline void blkg_stat_exit(struct blkg_stat *stat)
+{
+ percpu_counter_destroy(&stat->cpu_cnt);
}

/**
@@ -497,35 +510,21 @@ static inline void blkg_stat_init(struct blkg_stat *stat)
* @stat: target blkg_stat
* @val: value to add
*
- * Add @val to @stat. The caller is responsible for synchronizing calls to
- * this function.
+ * Add @val to @stat. The caller must ensure that IRQ on the same CPU
+ * don't re-enter this function for the same counter.
*/
static inline void blkg_stat_add(struct blkg_stat *stat, uint64_t val)
{
- u64_stats_update_begin(&stat->syncp);
- stat->cnt += val;
- u64_stats_update_end(&stat->syncp);
+ __percpu_counter_add(&stat->cpu_cnt, val, BLKG_STAT_CPU_BATCH);
}

/**
* blkg_stat_read - read the current value of a blkg_stat
* @stat: blkg_stat to read
- *
- * Read the current value of @stat. The returned value doesn't include the
- * aux count. This function can be called without synchroniztion and takes
- * care of u64 atomicity.
*/
static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
{
- unsigned int start;
- uint64_t v;
-
- do {
- start = u64_stats_fetch_begin_irq(&stat->syncp);
- v = stat->cnt;
- } while (u64_stats_fetch_retry_irq(&stat->syncp, start));
-
- return v;
+ return percpu_counter_sum_positive(&stat->cpu_cnt);
}

/**
@@ -534,7 +533,7 @@ static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
*/
static inline void blkg_stat_reset(struct blkg_stat *stat)
{
- stat->cnt = 0;
+ percpu_counter_set(&stat->cpu_cnt, 0);
atomic64_set(&stat->aux_cnt, 0);
}

@@ -552,14 +551,28 @@ static inline void blkg_stat_add_aux(struct blkg_stat *to,
&to->aux_cnt);
}

-static inline void blkg_rwstat_init(struct blkg_rwstat *rwstat)
+static inline int blkg_rwstat_init(struct blkg_rwstat *rwstat, gfp_t gfp)
{
- int i;
+ int i, ret;
+
+ for (i = 0; i < BLKG_RWSTAT_NR; i++) {
+ ret = percpu_counter_init(&rwstat->cpu_cnt[i], 0, gfp);
+ if (ret) {
+ while (--i >= 0)
+ percpu_counter_destroy(&rwstat->cpu_cnt[i]);
+ return ret;
+ }
+ atomic64_set(&rwstat->aux_cnt[i], 0);
+ }
+ return 0;
+}

- u64_stats_init(&rwstat->syncp);
+static inline void blkg_rwstat_exit(struct blkg_rwstat *rwstat)
+{
+ int i;

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_set(&rwstat->aux_cnt[i], 0);
+ percpu_counter_destroy(&rwstat->cpu_cnt[i]);
}

/**
@@ -574,39 +587,38 @@ static inline void blkg_rwstat_init(struct blkg_rwstat *rwstat)
static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
int rw, uint64_t val)
{
- u64_stats_update_begin(&rwstat->syncp);
+ struct percpu_counter *cnt;

if (rw & REQ_WRITE)
- rwstat->cnt[BLKG_RWSTAT_WRITE] += val;
+ cnt = &rwstat->cpu_cnt[BLKG_RWSTAT_WRITE];
else
- rwstat->cnt[BLKG_RWSTAT_READ] += val;
+ cnt = &rwstat->cpu_cnt[BLKG_RWSTAT_READ];
+
+ __percpu_counter_add(cnt, val, BLKG_STAT_CPU_BATCH);
+
if (rw & REQ_SYNC)
- rwstat->cnt[BLKG_RWSTAT_SYNC] += val;
+ cnt = &rwstat->cpu_cnt[BLKG_RWSTAT_SYNC];
else
- rwstat->cnt[BLKG_RWSTAT_ASYNC] += val;
+ cnt = &rwstat->cpu_cnt[BLKG_RWSTAT_ASYNC];

- u64_stats_update_end(&rwstat->syncp);
+ __percpu_counter_add(cnt, val, BLKG_STAT_CPU_BATCH);
}

/**
* blkg_rwstat_read - read the current values of a blkg_rwstat
* @rwstat: blkg_rwstat to read
*
- * Read the current snapshot of @rwstat and return it as the return value.
- * This function can be called without synchronization and takes care of
- * u64 atomicity.
+ * Read the current snapshot of @rwstat and return it in the aux counts.
*/
static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
{
- unsigned int start;
- struct blkg_rwstat tmp;
-
- do {
- start = u64_stats_fetch_begin_irq(&rwstat->syncp);
- tmp = *rwstat;
- } while (u64_stats_fetch_retry_irq(&rwstat->syncp, start));
+ struct blkg_rwstat result;
+ int i;

- return tmp;
+ for (i = 0; i < BLKG_RWSTAT_NR; i++)
+ atomic64_set(&result.aux_cnt[i],
+ percpu_counter_sum_positive(&rwstat->cpu_cnt[i]));
+ return result;
}

/**
@@ -621,7 +633,8 @@ static inline uint64_t blkg_rwstat_total(struct blkg_rwstat *rwstat)
{
struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);

- return tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE];
+ return atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
+ atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);
}

/**
@@ -632,10 +645,10 @@ static inline void blkg_rwstat_reset(struct blkg_rwstat *rwstat)
{
int i;

- memset(rwstat->cnt, 0, sizeof(rwstat->cnt));
-
- for (i = 0; i < BLKG_RWSTAT_NR; i++)
+ for (i = 0; i < BLKG_RWSTAT_NR; i++) {
+ percpu_counter_set(&rwstat->cpu_cnt[i], 0);
atomic64_set(&rwstat->aux_cnt[i], 0);
+ }
}

/**
@@ -652,7 +665,8 @@ static inline void blkg_rwstat_add_aux(struct blkg_rwstat *to,
int i;

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_add(v.cnt[i] + atomic64_read(&from->aux_cnt[i]),
+ atomic64_add(atomic64_read(&v.aux_cnt[i]) +
+ atomic64_read(&from->aux_cnt[i]),
&to->aux_cnt[i]);
}

--
2.4.3