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Subject[PATCH 3/6] blk-cgroup: introduce a new struct blkg_rwstat_sample
Date
When sampling the blkcg counts we don't need atomics or per-cpu
variables. Introduce a new structure just containing plain u64
counters.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/bfq-cgroup.c | 10 ++++------
block/blk-cgroup.c | 39 +++++++++++++++++++-------------------
include/linux/blk-cgroup.h | 22 +++++++++++----------
3 files changed, 35 insertions(+), 36 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 66abc82179f3..624374a99c6e 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -935,7 +935,7 @@ static u64 bfqg_prfill_stat_recursive(struct seq_file *sf,
static u64 bfqg_prfill_rwstat_recursive(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat sum;
+ struct blkg_rwstat_sample sum;

blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq, off, &sum);
return __blkg_prfill_rwstat(sf, pd, &sum);
@@ -975,15 +975,13 @@ static int bfqg_print_stat_sectors(struct seq_file *sf, void *v)
static u64 bfqg_prfill_sectors_recursive(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat tmp;
- u64 sum;
+ struct blkg_rwstat_sample tmp;

blkg_rwstat_recursive_sum(pd->blkg, NULL,
offsetof(struct blkcg_gq, stat_bytes), &tmp);
- sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
- atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);

- return __blkg_prfill_u64(sf, pd, sum >> 9);
+ return __blkg_prfill_u64(sf, pd,
+ (tmp.cnt[BLKG_RWSTAT_READ] + tmp.cnt[BLKG_RWSTAT_WRITE]) >> 9);
}

static int bfqg_print_stat_sectors_recursive(struct seq_file *sf, void *v)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 7d6bf9b03e24..aad0f5d9a2ea 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -549,7 +549,7 @@ EXPORT_SYMBOL_GPL(__blkg_prfill_u64);
* Print @rwstat to @sf for the device assocaited with @pd.
*/
u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
- const struct blkg_rwstat *rwstat)
+ const struct blkg_rwstat_sample *rwstat)
{
static const char *rwstr[] = {
[BLKG_RWSTAT_READ] = "Read",
@@ -567,12 +567,12 @@ 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)atomic64_read(&rwstat->aux_cnt[i]));
+ rwstat->cnt[i]);

- v = atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_READ]) +
- atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_WRITE]) +
- atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_DISCARD]);
- seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
+ v = rwstat->cnt[BLKG_RWSTAT_READ] +
+ rwstat->cnt[BLKG_RWSTAT_WRITE] +
+ rwstat->cnt[BLKG_RWSTAT_DISCARD];
+ seq_printf(sf, "%s Total %llu\n", dname, v);
return v;
}
EXPORT_SYMBOL_GPL(__blkg_prfill_rwstat);
@@ -602,7 +602,7 @@ EXPORT_SYMBOL_GPL(blkg_prfill_stat);
u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
int off)
{
- struct blkg_rwstat rwstat = { };
+ struct blkg_rwstat_sample rwstat = { };

blkg_rwstat_read((void *)pd + off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
@@ -612,7 +612,7 @@ EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
static u64 blkg_prfill_rwstat_field(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat rwstat = { };
+ struct blkg_rwstat_sample rwstat = { };

blkg_rwstat_read((void *)pd->blkg + off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
@@ -656,7 +656,7 @@ static u64 blkg_prfill_rwstat_field_recursive(struct seq_file *sf,
struct blkg_policy_data *pd,
int off)
{
- struct blkg_rwstat rwstat;
+ struct blkg_rwstat_sample rwstat;

blkg_rwstat_recursive_sum(pd->blkg, NULL, off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
@@ -739,7 +739,7 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
* @blkg: blkg of interest
* @pol: blkcg_policy which contains the blkg_rwstat
* @off: offset to the blkg_rwstat in blkg_policy_data or @blkg
- * @sum: blkg_rwstat structure containing the results
+ * @sum: blkg_rwstat_sample structure containing the results
*
* Collect the blkg_rwstat specified by @blkg, @pol and @off and all its
* online descendants and their aux counts. The caller must be holding the
@@ -749,7 +749,7 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
* is at @off bytes into @blkg's blkg_policy_data of the policy.
*/
void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
- int off, struct blkg_rwstat *sum)
+ int off, struct blkg_rwstat_sample *sum)
{
struct blkcg_gq *pos_blkg;
struct cgroup_subsys_state *pos_css;
@@ -770,8 +770,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
rwstat = (void *)pos_blkg + off;

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_set(&sum->aux_cnt[i],
- blkg_rwstat_read_counter(rwstat, i));
+ sum->cnt[i] = blkg_rwstat_read_counter(rwstat, i);
}
rcu_read_unlock();
}
@@ -939,7 +938,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
const char *dname;
char *buf;
- struct blkg_rwstat rwstat;
+ struct blkg_rwstat_sample rwstat;
u64 rbytes, wbytes, rios, wios, dbytes, dios;
size_t size = seq_get_buf(sf, &buf), off = 0;
int i;
@@ -961,15 +960,15 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)

blkg_rwstat_recursive_sum(blkg, NULL,
offsetof(struct blkcg_gq, stat_bytes), &rwstat);
- rbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
- wbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
- dbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);
+ rbytes = rwstat.cnt[BLKG_RWSTAT_READ];
+ wbytes = rwstat.cnt[BLKG_RWSTAT_WRITE];
+ dbytes = rwstat.cnt[BLKG_RWSTAT_DISCARD];

blkg_rwstat_recursive_sum(blkg, NULL,
offsetof(struct blkcg_gq, stat_ios), &rwstat);
- rios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
- wios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
- dios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);
+ rios = rwstat.cnt[BLKG_RWSTAT_READ];
+ wios = rwstat.cnt[BLKG_RWSTAT_WRITE];
+ dios = rwstat.cnt[BLKG_RWSTAT_DISCARD];

spin_unlock_irq(&blkg->q->queue_lock);

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 3ee858111274..e4a81767e111 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -63,8 +63,7 @@ struct blkcg {

/*
* blkg_[rw]stat->aux_cnt is excluded for local stats but included for
- * recursive. Used to carry stats of dead children, and, for blkg_rwstat,
- * to carry result values from read and sum operations.
+ * recursive. Used to carry stats of dead children.
*/
struct blkg_stat {
struct percpu_counter cpu_cnt;
@@ -76,6 +75,10 @@ struct blkg_rwstat {
atomic64_t aux_cnt[BLKG_RWSTAT_NR];
};

+struct blkg_rwstat_sample {
+ u64 cnt[BLKG_RWSTAT_NR];
+};
+
/*
* A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
* request_queue (q). This is used by blkcg policies which need to track
@@ -213,7 +216,7 @@ void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
bool show_total);
u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
u64 __blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
- const struct blkg_rwstat *rwstat);
+ const struct blkg_rwstat_sample *rwstat);
u64 blkg_prfill_stat(struct seq_file *sf, struct blkg_policy_data *pd, int off);
u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
int off);
@@ -225,7 +228,7 @@ int blkg_print_stat_ios_recursive(struct seq_file *sf, void *v);
u64 blkg_stat_recursive_sum(struct blkcg_gq *blkg,
struct blkcg_policy *pol, int off);
void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
- int off, struct blkg_rwstat *sum);
+ int off, struct blkg_rwstat_sample *sum);

struct blkg_conf_ctx {
struct gendisk *disk;
@@ -701,13 +704,13 @@ static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
* Read the current snapshot of @rwstat and return it in the aux counts.
*/
static inline void blkg_rwstat_read(struct blkg_rwstat *rwstat,
- struct blkg_rwstat *result)
+ struct blkg_rwstat_sample *result)
{
int i;

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

/**
@@ -720,11 +723,10 @@ static inline void blkg_rwstat_read(struct blkg_rwstat *rwstat,
*/
static inline uint64_t blkg_rwstat_total(struct blkg_rwstat *rwstat)
{
- struct blkg_rwstat tmp = { };
+ struct blkg_rwstat_sample tmp = { };

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

/**
--
2.20.1
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