blk-cgroup: introduce a new struct blkg_rwstat_sample

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>

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 66abc82..624374a 100644 (file)
--- 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 db039a8..664c098 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -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",
@@ -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);
@@ -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);
@@ -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);
@@ -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);
@@ -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
@@ -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;
@@ -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();
 }
@@ -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;
@@ -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);
 

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 3ee8581..e4a8176 100644 (file)
--- 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];
 }
 
 /**