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Subject[PATCH v2 2/2] blk-stats: Introduce explicit stat staging buffers
Date
From: Pavel Begunkov <asml.silence@gmail.com>

Split struct blk_rq_stat into 2:
1. struct blk_rq_stat_staging is for intermediate/staging stats.
These are usually per-cpu and in a hot-path
2. struct blk_rq_stat for accumulating staging stats

That duplicates code, but
1. prevents misuses (compile-time check by type-system)
2. reduces memory needed (inc. per-cpu)
3. makes it easier to extend stats

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
block/blk-iolatency.c | 41 +++++++++++++++++++++++++++++----------
block/blk-stat.c | 30 +++++++++++++++++-----------
block/blk-stat.h | 8 +++++---
include/linux/blk_types.h | 6 ++++++
4 files changed, 61 insertions(+), 24 deletions(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 895c6e955f97..08a32dc4a7d6 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -130,9 +130,16 @@ struct latency_stat {
};
};

+struct latency_stat_staging {
+ union {
+ struct percentile_stats ps;
+ struct blk_rq_stat_staging rqs;
+ };
+};
+
struct iolatency_grp {
struct blkg_policy_data pd;
- struct latency_stat __percpu *stats;
+ struct latency_stat_staging __percpu *stats;
struct latency_stat cur_stat;
struct blk_iolatency *blkiolat;
struct rq_depth rq_depth;
@@ -199,6 +206,16 @@ static inline void latency_stat_init(struct iolatency_grp *iolat,
blk_rq_stat_init(&stat->rqs);
}

+static inline void latency_stat_init_staging(struct iolatency_grp *iolat,
+ struct latency_stat_staging *stat)
+{
+ if (iolat->ssd) {
+ stat->ps.total = 0;
+ stat->ps.missed = 0;
+ } else
+ blk_rq_stat_init_staging(&stat->rqs);
+}
+
static inline void latency_stat_merge(struct iolatency_grp *iolat,
struct latency_stat *sum,
struct latency_stat *stat)
@@ -212,7 +229,7 @@ static inline void latency_stat_merge(struct iolatency_grp *iolat,

static inline void latency_stat_collect(struct iolatency_grp *iolat,
struct latency_stat *sum,
- struct latency_stat *stat)
+ struct latency_stat_staging *stat)
{
if (iolat->ssd) {
sum->ps.total += stat->ps.total;
@@ -224,7 +241,8 @@ static inline void latency_stat_collect(struct iolatency_grp *iolat,
static inline void latency_stat_record_time(struct iolatency_grp *iolat,
u64 req_time)
{
- struct latency_stat *stat = get_cpu_ptr(iolat->stats);
+ struct latency_stat_staging *stat = get_cpu_ptr(iolat->stats);
+
if (iolat->ssd) {
if (req_time >= iolat->min_lat_nsec)
stat->ps.missed++;
@@ -540,10 +558,11 @@ static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
latency_stat_init(iolat, &stat);
preempt_disable();
for_each_online_cpu(cpu) {
- struct latency_stat *s;
+ struct latency_stat_staging *s;
+
s = per_cpu_ptr(iolat->stats, cpu);
latency_stat_collect(iolat, &stat, s);
- latency_stat_init(iolat, s);
+ latency_stat_init_staging(iolat, s);
}
preempt_enable();

@@ -905,7 +924,8 @@ static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf,
latency_stat_init(iolat, &stat);
preempt_disable();
for_each_online_cpu(cpu) {
- struct latency_stat *s;
+ struct latency_stat_staging *s;
+
s = per_cpu_ptr(iolat->stats, cpu);
latency_stat_collect(iolat, &stat, s);
}
@@ -954,8 +974,8 @@ static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp,
iolat = kzalloc_node(sizeof(*iolat), gfp, q->node);
if (!iolat)
return NULL;
- iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat),
- __alignof__(struct latency_stat), gfp);
+ iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat_staging),
+ __alignof__(struct latency_stat_staging), gfp);
if (!iolat->stats) {
kfree(iolat);
return NULL;
@@ -978,9 +998,10 @@ static void iolatency_pd_init(struct blkg_policy_data *pd)
iolat->ssd = false;

for_each_possible_cpu(cpu) {
- struct latency_stat *stat;
+ struct latency_stat_staging *stat;
+
stat = per_cpu_ptr(iolat->stats, cpu);
- latency_stat_init(iolat, stat);
+ latency_stat_init_staging(iolat, stat);
}

latency_stat_init(iolat, &iolat->cur_stat);
diff --git a/block/blk-stat.c b/block/blk-stat.c
index 78389182b5d0..d892ad2cb938 100644
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -18,15 +18,22 @@ struct blk_queue_stats {
bool enable_accounting;
};

+void blk_rq_stat_init_staging(struct blk_rq_stat_staging *stat)
+{
+ stat->min = -1ULL;
+ stat->max = 0;
+ stat->batch = 0;
+ stat->nr_samples = 0;
+}
+
void blk_rq_stat_init(struct blk_rq_stat *stat)
{
stat->min = -1ULL;
stat->max = stat->nr_samples = stat->mean = 0;
- stat->batch = 0;
}

-/* src is a per-cpu stat, mean isn't initialized */
-void blk_rq_stat_collect(struct blk_rq_stat *dst, struct blk_rq_stat *src)
+void blk_rq_stat_collect(struct blk_rq_stat *dst,
+ struct blk_rq_stat_staging *src)
{
if (!src->nr_samples)
return;
@@ -55,7 +62,7 @@ void blk_rq_stat_merge(struct blk_rq_stat *dst, struct blk_rq_stat *src)
dst->nr_samples += src->nr_samples;
}

-void blk_rq_stat_add(struct blk_rq_stat *stat, u64 value)
+void blk_rq_stat_add(struct blk_rq_stat_staging *stat, u64 value)
{
stat->min = min(stat->min, value);
stat->max = max(stat->max, value);
@@ -67,7 +74,7 @@ void blk_stat_add(struct request *rq, u64 now)
{
struct request_queue *q = rq->q;
struct blk_stat_callback *cb;
- struct blk_rq_stat *stat;
+ struct blk_rq_stat_staging *stat;
int bucket;
u64 value;

@@ -101,13 +108,13 @@ static void blk_stat_timer_fn(struct timer_list *t)
blk_rq_stat_init(&cb->stat[bucket]);

for_each_online_cpu(cpu) {
- struct blk_rq_stat *cpu_stat;
+ struct blk_rq_stat_staging *cpu_stat;

cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
for (bucket = 0; bucket < cb->buckets; bucket++) {
blk_rq_stat_collect(&cb->stat[bucket],
&cpu_stat[bucket]);
- blk_rq_stat_init(&cpu_stat[bucket]);
+ blk_rq_stat_init_staging(&cpu_stat[bucket]);
}
}

@@ -131,8 +138,9 @@ blk_stat_alloc_callback(void (*timer_fn)(struct blk_stat_callback *),
kfree(cb);
return NULL;
}
- cb->cpu_stat = __alloc_percpu(buckets * sizeof(struct blk_rq_stat),
- __alignof__(struct blk_rq_stat));
+ cb->cpu_stat = __alloc_percpu(
+ buckets * sizeof(struct blk_rq_stat_staging),
+ __alignof__(struct blk_rq_stat_staging));
if (!cb->cpu_stat) {
kfree(cb->stat);
kfree(cb);
@@ -155,11 +163,11 @@ void blk_stat_add_callback(struct request_queue *q,
int cpu;

for_each_possible_cpu(cpu) {
- struct blk_rq_stat *cpu_stat;
+ struct blk_rq_stat_staging *cpu_stat;

cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
for (bucket = 0; bucket < cb->buckets; bucket++)
- blk_rq_stat_init(&cpu_stat[bucket]);
+ blk_rq_stat_init_staging(&cpu_stat[bucket]);
}

spin_lock(&q->stats->lock);
diff --git a/block/blk-stat.h b/block/blk-stat.h
index 5597ecc34ef5..e5c753fbd6e6 100644
--- a/block/blk-stat.h
+++ b/block/blk-stat.h
@@ -30,7 +30,7 @@ struct blk_stat_callback {
/**
* @cpu_stat: Per-cpu statistics buckets.
*/
- struct blk_rq_stat __percpu *cpu_stat;
+ struct blk_rq_stat_staging __percpu *cpu_stat;

/**
* @bucket_fn: Given a request, returns which statistics bucket it
@@ -164,9 +164,11 @@ static inline void blk_stat_activate_msecs(struct blk_stat_callback *cb,
mod_timer(&cb->timer, jiffies + msecs_to_jiffies(msecs));
}

-void blk_rq_stat_add(struct blk_rq_stat *, u64);
-void blk_rq_stat_collect(struct blk_rq_stat *dst, struct blk_rq_stat *src);
+void blk_rq_stat_add(struct blk_rq_stat_staging *stat, u64);
+void blk_rq_stat_collect(struct blk_rq_stat *dst,
+ struct blk_rq_stat_staging *src);
void blk_rq_stat_merge(struct blk_rq_stat *dst, struct blk_rq_stat *src);
void blk_rq_stat_init(struct blk_rq_stat *);
+void blk_rq_stat_init_staging(struct blk_rq_stat_staging *stat);

#endif
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 6f7a8647cefb..5a7d8b70fcf0 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -452,7 +452,13 @@ struct blk_rq_stat {
u64 min;
u64 max;
u32 nr_samples;
+};
+
+struct blk_rq_stat_staging {
+ u64 min;
+ u64 max;
u64 batch;
+ u32 nr_samples;
};

#endif /* __LINUX_BLK_TYPES_H */
--
2.22.0
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