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>

2 files changed, 23 insertions, 26 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 db039a869d95..664c09866839 100644
--- 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);