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

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Christoph Hellwig authored and Jens Axboe committed Jun 20, 2019
1 parent 5d0b6e4 commit 7af6fd9
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Showing 3 changed files with 35 additions and 36 deletions.
10 changes: 4 additions & 6 deletions block/bfq-cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -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)
Expand Down
39 changes: 19 additions & 20 deletions block/blk-cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -544,7 +544,7 @@ 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",
Expand All @@ -562,12 +562,12 @@ 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);
Expand Down Expand Up @@ -597,7 +597,7 @@ 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);
Expand All @@ -607,7 +607,7 @@ 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);
Expand Down Expand Up @@ -651,7 +651,7 @@ 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);
Expand Down Expand Up @@ -734,7 +734,7 @@ 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
Expand All @@ -744,7 +744,7 @@ 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;
Expand All @@ -765,8 +765,7 @@ 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();
}
Expand Down Expand Up @@ -934,7 +933,7 @@ 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;
Expand All @@ -956,15 +955,15 @@ 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);

Expand Down
22 changes: 12 additions & 10 deletions include/linux/blk-cgroup.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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
Expand Down Expand Up @@ -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);
Expand All @@ -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;
Expand Down Expand Up @@ -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]);
}

/**
Expand All @@ -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];
}

/**
Expand Down

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