blkcg: cfq doesn't need per-cpu dispatch stats

blkio_group_stats_cpu is used to count dispatch stats using per-cpu
counters.  This is used by both blk-throtl and cfq-iosched but the
sharing is rather silly.

* cfq-iosched doesn't need per-cpu dispatch stats.  cfq always updates
  those stats while holding queue_lock.

* blk-throtl needs per-cpu dispatch stats but only service_bytes and
  serviced.  It doesn't make use of sectors.

This patch makes cfq add and use global stats for service_bytes,
serviced and sectors, removes per-cpu sectors counter and moves
per-cpu stat printing code to blk-throttle.c.

Signed-off-by: Tejun Heo <tj@kernel.org>

4 files changed, 48 insertions, 95 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 821a0a393e85..19ee29f1b7c5 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -390,7 +390,6 @@ static void blkio_reset_stats_cpu(struct blkio_group *blkg, int plid)
 
                 blkg_rwstat_reset(&sc->service_bytes);
                 blkg_rwstat_reset(&sc->serviced);
-                blkg_stat_reset(&sc->sectors);
         }
 }
 
@@ -417,6 +416,8 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
                         struct blkio_group_stats *stats = &pd->stats;
 
                         /* queued stats shouldn't be cleared */
+                        blkg_rwstat_reset(&stats->service_bytes);
+                        blkg_rwstat_reset(&stats->serviced);
                         blkg_rwstat_reset(&stats->merged);
                         blkg_rwstat_reset(&stats->service_time);
                         blkg_rwstat_reset(&stats->wait_time);
@@ -577,66 +578,6 @@ int blkcg_print_rwstat(struct cgroup *cgrp, struct cftype *cft,
 }
 EXPORT_SYMBOL_GPL(blkcg_print_rwstat);
 
-static u64 blkg_prfill_cpu_stat(struct seq_file *sf,
-                                struct blkg_policy_data *pd, int off)
-{
-        u64 v = 0;
-        int cpu;
-
-        for_each_possible_cpu(cpu) {
-                struct blkio_group_stats_cpu *sc =
-                        per_cpu_ptr(pd->stats_cpu, cpu);
-
-                v += blkg_stat_read((void *)sc + off);
-        }
-
-        return __blkg_prfill_u64(sf, pd, v);
-}
-
-static u64 blkg_prfill_cpu_rwstat(struct seq_file *sf,
-                                  struct blkg_policy_data *pd, int off)
-{
-        struct blkg_rwstat rwstat = { }, tmp;
-        int i, cpu;
-
-        for_each_possible_cpu(cpu) {
-                struct blkio_group_stats_cpu *sc =
-                        per_cpu_ptr(pd->stats_cpu, cpu);
-
-                tmp = blkg_rwstat_read((void *)sc + off);
-                for (i = 0; i < BLKG_RWSTAT_NR; i++)
-                        rwstat.cnt[i] += tmp.cnt[i];
-        }
-
-        return __blkg_prfill_rwstat(sf, pd, &rwstat);
-}
-
-/* print per-cpu blkg_stat specified by BLKCG_STAT_PRIV() */
-int blkcg_print_cpu_stat(struct cgroup *cgrp, struct cftype *cft,
-                         struct seq_file *sf)
-{
-        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);
-
-        blkcg_print_blkgs(sf, blkcg, blkg_prfill_cpu_stat,
-                          BLKCG_STAT_POL(cft->private),
-                          BLKCG_STAT_OFF(cft->private), false);
-        return 0;
-}
-EXPORT_SYMBOL_GPL(blkcg_print_cpu_stat);
-
-/* print per-cpu blkg_rwstat specified by BLKCG_STAT_PRIV() */
-int blkcg_print_cpu_rwstat(struct cgroup *cgrp, struct cftype *cft,
-                           struct seq_file *sf)
-{
-        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);
-
-        blkcg_print_blkgs(sf, blkcg, blkg_prfill_cpu_rwstat,
-                          BLKCG_STAT_POL(cft->private),
-                          BLKCG_STAT_OFF(cft->private), true);
-        return 0;
-}
-EXPORT_SYMBOL_GPL(blkcg_print_cpu_rwstat);
-
 /**
  * blkg_conf_prep - parse and prepare for per-blkg config update
  * @blkcg: target block cgroup
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 0b0a176ee007..c82de47ae69f 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -65,6 +65,10 @@ struct blkg_rwstat {
 };
 
 struct blkio_group_stats {
+        /* total bytes transferred */
+        struct blkg_rwstat              service_bytes;
+        /* total IOs serviced, post merge */
+        struct blkg_rwstat              serviced;
         /* number of ios merged */
         struct blkg_rwstat              merged;
         /* total time spent on device in ns, may not be accurate w/ queueing */
@@ -73,6 +77,8 @@ struct blkio_group_stats {
         struct blkg_rwstat              wait_time;
         /* number of IOs queued up */
         struct blkg_rwstat              queued;
+        /* total sectors transferred */
+        struct blkg_stat                sectors;
         /* total disk time and nr sectors dispatched by this group */
         struct blkg_stat                time;
 #ifdef CONFIG_DEBUG_BLK_CGROUP
@@ -104,8 +110,6 @@ struct blkio_group_stats_cpu {
         struct blkg_rwstat              service_bytes;
         /* total IOs serviced, post merge */
         struct blkg_rwstat              serviced;
-        /* total sectors transferred */
-        struct blkg_stat                sectors;
 };
 
 struct blkio_group_conf {
@@ -183,10 +187,6 @@ int blkcg_print_stat(struct cgroup *cgrp, struct cftype *cft,
                      struct seq_file *sf);
 int blkcg_print_rwstat(struct cgroup *cgrp, struct cftype *cft,
                        struct seq_file *sf);
-int blkcg_print_cpu_stat(struct cgroup *cgrp, struct cftype *cft,
-                         struct seq_file *sf);
-int blkcg_print_cpu_rwstat(struct cgroup *cgrp, struct cftype *cft,
-                           struct seq_file *sf);
 
 struct blkg_conf_ctx {
         struct gendisk          *disk;
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 5d647edc02a1..cb259bc46f43 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -582,7 +582,6 @@ static void throtl_update_dispatch_stats(struct blkio_group *blkg, u64 bytes,
 
         stats_cpu = this_cpu_ptr(pd->stats_cpu);
 
-        blkg_stat_add(&stats_cpu->sectors, bytes >> 9);
         blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
         blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);
 
@@ -843,6 +842,36 @@ static void throtl_update_blkio_group_common(struct throtl_data *td,
         throtl_schedule_delayed_work(td, 0);
 }
 
+static u64 blkg_prfill_cpu_rwstat(struct seq_file *sf,
+                                  struct blkg_policy_data *pd, int off)
+{
+        struct blkg_rwstat rwstat = { }, tmp;
+        int i, cpu;
+
+        for_each_possible_cpu(cpu) {
+                struct blkio_group_stats_cpu *sc =
+                        per_cpu_ptr(pd->stats_cpu, cpu);
+
+                tmp = blkg_rwstat_read((void *)sc + off);
+                for (i = 0; i < BLKG_RWSTAT_NR; i++)
+                        rwstat.cnt[i] += tmp.cnt[i];
+        }
+
+        return __blkg_prfill_rwstat(sf, pd, &rwstat);
+}
+
+/* print per-cpu blkg_rwstat specified by BLKCG_STAT_PRIV() */
+static int blkcg_print_cpu_rwstat(struct cgroup *cgrp, struct cftype *cft,
+                                  struct seq_file *sf)
+{
+        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgrp);
+
+        blkcg_print_blkgs(sf, blkcg, blkg_prfill_cpu_rwstat,
+                          BLKCG_STAT_POL(cft->private),
+                          BLKCG_STAT_OFF(cft->private), true);
+        return 0;
+}
+
 static u64 blkg_prfill_conf_u64(struct seq_file *sf,
                                 struct blkg_policy_data *pd, int off)
 {
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 49913804e8dd..effd89489506 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -624,29 +624,12 @@ static inline void cfq_blkiocg_update_dispatch_stats(struct blkio_group *blkg,
                         struct blkio_policy_type *pol, uint64_t bytes,
                         bool direction, bool sync)
 {
+        struct blkio_group_stats *stats = &blkg->pd[pol->plid]->stats;
         int rw = (direction ? REQ_WRITE : 0) | (sync ? REQ_SYNC : 0);
-        struct blkg_policy_data *pd = blkg->pd[pol->plid];
-        struct blkio_group_stats_cpu *stats_cpu;
-        unsigned long flags;
 
-        /* If per cpu stats are not allocated yet, don't do any accounting. */
-        if (pd->stats_cpu == NULL)
-                return;
-
-        /*
-         * Disabling interrupts to provide mutual exclusion between two
-         * writes on same cpu. It probably is not needed for 64bit. Not
-         * optimizing that case yet.
-         */
-        local_irq_save(flags);
-
-        stats_cpu = this_cpu_ptr(pd->stats_cpu);
-
-        blkg_stat_add(&stats_cpu->sectors, bytes >> 9);
-        blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
-        blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);
-
-        local_irq_restore(flags);
+        blkg_stat_add(&stats->sectors, bytes >> 9);
+        blkg_rwstat_add(&stats->serviced, rw, 1);
+        blkg_rwstat_add(&stats->service_bytes, rw, bytes);
 }
 
 static inline void cfq_blkiocg_update_completion_stats(struct blkio_group *blkg,
@@ -1520,20 +1503,20 @@ static struct cftype cfq_blkcg_files[] = {
         {
                 .name = "sectors",
                 .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
-                                offsetof(struct blkio_group_stats_cpu, sectors)),
-                .read_seq_string = blkcg_print_cpu_stat,
+                                offsetof(struct blkio_group_stats, sectors)),
+                .read_seq_string = blkcg_print_stat,
         },
         {
                 .name = "io_service_bytes",
                 .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
-                                offsetof(struct blkio_group_stats_cpu, service_bytes)),
-                .read_seq_string = blkcg_print_cpu_rwstat,
+                                offsetof(struct blkio_group_stats, service_bytes)),
+                .read_seq_string = blkcg_print_rwstat,
         },
         {
                 .name = "io_serviced",
                 .private = BLKCG_STAT_PRIV(BLKIO_POLICY_PROP,
-                                offsetof(struct blkio_group_stats_cpu, serviced)),
-                .read_seq_string = blkcg_print_cpu_rwstat,
+                                offsetof(struct blkio_group_stats, serviced)),
+                .read_seq_string = blkcg_print_rwstat,
         },
         {
                 .name = "io_service_time",