block, bfq: move debug blkio stats behind CONFIG_DEBUG_BLK_CGROUP

BFQ currently creates, and updates, its own instance of the whole
set of blkio statistics that cfq creates. Yet, from the comments
of Tejun Heo in [1], it turned out that most of these statistics
are meant/useful only for debugging. This commit makes BFQ create
the latter, debugging statistics only if the option
CONFIG_DEBUG_BLK_CGROUP is set.

By doing so, this commit also enables BFQ to enjoy a high perfomance
boost. The reason is that, if CONFIG_DEBUG_BLK_CGROUP is not set, then
BFQ has to update far fewer statistics, and, in particular, not the
heaviest to update.  To give an idea of the benefits, if
CONFIG_DEBUG_BLK_CGROUP is not set, then, on an Intel i7-4850HQ, and
with 8 threads doing random I/O in parallel on null_blk (configured
with 0 latency), the throughput of BFQ grows from 310 to 400 KIOPS
(+30%). We have measured similar or even much higher boosts with other
CPUs: e.g., +45% with an ARM CortexTM-A53 Octa-core. Our results have
been obtained and can be reproduced very easily with the script in [1].

[1] https://www.spinics.net/lists/linux-block/msg18943.html

Suggested-by: Tejun Heo <tj@kernel.org>
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Lee Tibbert <lee.tibbert@gmail.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 84 insertions, 64 deletions

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index ceefb9a706d6..da1525ec4c87 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -24,7 +24,7 @@
 
 #include "bfq-iosched.h"
 
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
+#if defined(CONFIG_BFQ_GROUP_IOSCHED) &&  defined(CONFIG_DEBUG_BLK_CGROUP)
 
 /* bfqg stats flags */
 enum bfqg_stats_flags {
@@ -152,6 +152,57 @@ void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg)
         bfqg_stats_update_group_wait_time(stats);
 }
 
+void bfqg_stats_update_io_add(struct bfq_group *bfqg, struct bfq_queue *bfqq,
+                              unsigned int op)
+{
+        blkg_rwstat_add(&bfqg->stats.queued, op, 1);
+        bfqg_stats_end_empty_time(&bfqg->stats);
+        if (!(bfqq == ((struct bfq_data *)bfqg->bfqd)->in_service_queue))
+                bfqg_stats_set_start_group_wait_time(bfqg, bfqq_group(bfqq));
+}
+
+void bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op)
+{
+        blkg_rwstat_add(&bfqg->stats.queued, op, -1);
+}
+
+void bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op)
+{
+        blkg_rwstat_add(&bfqg->stats.merged, op, 1);
+}
+
+void bfqg_stats_update_completion(struct bfq_group *bfqg, uint64_t start_time,
+                                  uint64_t io_start_time, unsigned int op)
+{
+        struct bfqg_stats *stats = &bfqg->stats;
+        unsigned long long now = sched_clock();
+
+        if (time_after64(now, io_start_time))
+                blkg_rwstat_add(&stats->service_time, op,
+                                now - io_start_time);
+        if (time_after64(io_start_time, start_time))
+                blkg_rwstat_add(&stats->wait_time, op,
+                                io_start_time - start_time);
+}
+
+#else /* CONFIG_BFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */
+
+void bfqg_stats_update_io_add(struct bfq_group *bfqg, struct bfq_queue *bfqq,
+                              unsigned int op) { }
+void bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op) { }
+void bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op) { }
+void bfqg_stats_update_completion(struct bfq_group *bfqg, uint64_t start_time,
+                                  uint64_t io_start_time, unsigned int op) { }
+void bfqg_stats_update_dequeue(struct bfq_group *bfqg) { }
+void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg) { }
+void bfqg_stats_update_idle_time(struct bfq_group *bfqg) { }
+void bfqg_stats_set_start_idle_time(struct bfq_group *bfqg) { }
+void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg) { }
+
+#endif /* CONFIG_BFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */
+
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+
 /*
  * blk-cgroup policy-related handlers
  * The following functions help in converting between blk-cgroup
@@ -229,42 +280,10 @@ void bfqg_and_blkg_put(struct bfq_group *bfqg)
         blkg_put(bfqg_to_blkg(bfqg));
 }
 
-void bfqg_stats_update_io_add(struct bfq_group *bfqg, struct bfq_queue *bfqq,
-                              unsigned int op)
-{
-        blkg_rwstat_add(&bfqg->stats.queued, op, 1);
-        bfqg_stats_end_empty_time(&bfqg->stats);
-        if (!(bfqq == ((struct bfq_data *)bfqg->bfqd)->in_service_queue))
-                bfqg_stats_set_start_group_wait_time(bfqg, bfqq_group(bfqq));
-}
-
-void bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op)
-{
-        blkg_rwstat_add(&bfqg->stats.queued, op, -1);
-}
-
-void bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op)
-{
-        blkg_rwstat_add(&bfqg->stats.merged, op, 1);
-}
-
-void bfqg_stats_update_completion(struct bfq_group *bfqg, uint64_t start_time,
-                                  uint64_t io_start_time, unsigned int op)
-{
-        struct bfqg_stats *stats = &bfqg->stats;
-        unsigned long long now = sched_clock();
-
-        if (time_after64(now, io_start_time))
-                blkg_rwstat_add(&stats->service_time, op,
-                                now - io_start_time);
-        if (time_after64(io_start_time, start_time))
-                blkg_rwstat_add(&stats->wait_time, op,
-                                io_start_time - start_time);
-}
-
 /* @stats = 0 */
 static void bfqg_stats_reset(struct bfqg_stats *stats)
 {
+#ifdef CONFIG_DEBUG_BLK_CGROUP
         /* queued stats shouldn't be cleared */
         blkg_rwstat_reset(&stats->merged);
         blkg_rwstat_reset(&stats->service_time);
@@ -276,6 +295,7 @@ static void bfqg_stats_reset(struct bfqg_stats *stats)
         blkg_stat_reset(&stats->group_wait_time);
         blkg_stat_reset(&stats->idle_time);
         blkg_stat_reset(&stats->empty_time);
+#endif
 }
 
 /* @to += @from */
@@ -284,6 +304,7 @@ static void bfqg_stats_add_aux(struct bfqg_stats *to, struct bfqg_stats *from)
         if (!to || !from)
                 return;
 
+#ifdef CONFIG_DEBUG_BLK_CGROUP
         /* queued stats shouldn't be cleared */
         blkg_rwstat_add_aux(&to->merged, &from->merged);
         blkg_rwstat_add_aux(&to->service_time, &from->service_time);
@@ -296,6 +317,7 @@ static void bfqg_stats_add_aux(struct bfqg_stats *to, struct bfqg_stats *from)
         blkg_stat_add_aux(&to->group_wait_time, &from->group_wait_time);
         blkg_stat_add_aux(&to->idle_time, &from->idle_time);
         blkg_stat_add_aux(&to->empty_time, &from->empty_time);
+#endif
 }
 
 /*
@@ -342,6 +364,7 @@ void bfq_init_entity(struct bfq_entity *entity, struct bfq_group *bfqg)
 
 static void bfqg_stats_exit(struct bfqg_stats *stats)
 {
+#ifdef CONFIG_DEBUG_BLK_CGROUP
         blkg_rwstat_exit(&stats->merged);
         blkg_rwstat_exit(&stats->service_time);
         blkg_rwstat_exit(&stats->wait_time);
@@ -353,10 +376,12 @@ static void bfqg_stats_exit(struct bfqg_stats *stats)
         blkg_stat_exit(&stats->group_wait_time);
         blkg_stat_exit(&stats->idle_time);
         blkg_stat_exit(&stats->empty_time);
+#endif
 }
 
 static int bfqg_stats_init(struct bfqg_stats *stats, gfp_t gfp)
 {
+#ifdef CONFIG_DEBUG_BLK_CGROUP
         if (blkg_rwstat_init(&stats->merged, gfp) ||
             blkg_rwstat_init(&stats->service_time, gfp) ||
             blkg_rwstat_init(&stats->wait_time, gfp) ||
@@ -371,6 +396,7 @@ static int bfqg_stats_init(struct bfqg_stats *stats, gfp_t gfp)
                 bfqg_stats_exit(stats);
                 return -ENOMEM;
         }
+#endif
 
         return 0;
 }
@@ -887,6 +913,7 @@ static ssize_t bfq_io_set_weight(struct kernfs_open_file *of,
         return bfq_io_set_weight_legacy(of_css(of), NULL, weight);
 }
 
+#ifdef CONFIG_DEBUG_BLK_CGROUP
 static int bfqg_print_stat(struct seq_file *sf, void *v)
 {
         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), blkg_prfill_stat,
@@ -991,6 +1018,7 @@ static int bfqg_print_avg_queue_size(struct seq_file *sf, void *v)
                           0, false);
         return 0;
 }
+#endif /* CONFIG_DEBUG_BLK_CGROUP */
 
 struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node)
 {
@@ -1029,15 +1057,6 @@ struct cftype bfq_blkcg_legacy_files[] = {
 
         /* statistics, covers only the tasks in the bfqg */
         {
-                .name = "bfq.time",
-                .private = offsetof(struct bfq_group, stats.time),
-                .seq_show = bfqg_print_stat,
-        },
-        {
-                .name = "bfq.sectors",
-                .seq_show = bfqg_print_stat_sectors,
-        },
-        {
                 .name = "bfq.io_service_bytes",
                 .private = (unsigned long)&blkcg_policy_bfq,
                 .seq_show = blkg_print_stat_bytes,
@@ -1047,6 +1066,16 @@ struct cftype bfq_blkcg_legacy_files[] = {
                 .private = (unsigned long)&blkcg_policy_bfq,
                 .seq_show = blkg_print_stat_ios,
         },
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+        {
+                .name = "bfq.time",
+                .private = offsetof(struct bfq_group, stats.time),
+                .seq_show = bfqg_print_stat,
+        },
+        {
+                .name = "bfq.sectors",
+                .seq_show = bfqg_print_stat_sectors,
+        },
         {
                 .name = "bfq.io_service_time",
                 .private = offsetof(struct bfq_group, stats.service_time),
@@ -1067,18 +1096,10 @@ struct cftype bfq_blkcg_legacy_files[] = {
                 .private = offsetof(struct bfq_group, stats.queued),
                 .seq_show = bfqg_print_rwstat,
         },
+#endif /* CONFIG_DEBUG_BLK_CGROUP */
 
         /* the same statictics which cover the bfqg and its descendants */
         {
-                .name = "bfq.time_recursive",
-                .private = offsetof(struct bfq_group, stats.time),
-                .seq_show = bfqg_print_stat_recursive,
-        },
-        {
-                .name = "bfq.sectors_recursive",
-                .seq_show = bfqg_print_stat_sectors_recursive,
-        },
-        {
                 .name = "bfq.io_service_bytes_recursive",
                 .private = (unsigned long)&blkcg_policy_bfq,
                 .seq_show = blkg_print_stat_bytes_recursive,
@@ -1088,6 +1109,16 @@ struct cftype bfq_blkcg_legacy_files[] = {
                 .private = (unsigned long)&blkcg_policy_bfq,
                 .seq_show = blkg_print_stat_ios_recursive,
         },
+#ifdef CONFIG_DEBUG_BLK_CGROUP
+        {
+                .name = "bfq.time_recursive",
+                .private = offsetof(struct bfq_group, stats.time),
+                .seq_show = bfqg_print_stat_recursive,
+        },
+        {
+                .name = "bfq.sectors_recursive",
+                .seq_show = bfqg_print_stat_sectors_recursive,
+        },
         {
                 .name = "bfq.io_service_time_recursive",
                 .private = offsetof(struct bfq_group, stats.service_time),
@@ -1132,6 +1163,7 @@ struct cftype bfq_blkcg_legacy_files[] = {
                 .private = offsetof(struct bfq_group, stats.dequeue),
                 .seq_show = bfqg_print_stat,
         },
+#endif  /* CONFIG_DEBUG_BLK_CGROUP */
         { }     /* terminate */
 };
 
@@ -1147,18 +1179,6 @@ struct cftype bfq_blkg_files[] = {
 
 #else   /* CONFIG_BFQ_GROUP_IOSCHED */
 
-void bfqg_stats_update_io_add(struct bfq_group *bfqg, struct bfq_queue *bfqq,
-                              unsigned int op) { }
-void bfqg_stats_update_io_remove(struct bfq_group *bfqg, unsigned int op) { }
-void bfqg_stats_update_io_merged(struct bfq_group *bfqg, unsigned int op) { }
-void bfqg_stats_update_completion(struct bfq_group *bfqg, uint64_t start_time,
-                                  uint64_t io_start_time, unsigned int op) { }
-void bfqg_stats_update_dequeue(struct bfq_group *bfqg) { }
-void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg) { }
-void bfqg_stats_update_idle_time(struct bfq_group *bfqg) { }
-void bfqg_stats_set_start_idle_time(struct bfq_group *bfqg) { }
-void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg) { }
-
 void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                    struct bfq_group *bfqg) {}