blkcg: make blkcg_[rw]stat per-cpu

blkcg_[rw]stat are used as stat counters for blkcg policies.  It isn't
per-cpu by itself and blk-throttle makes it per-cpu by wrapping around
it.  This patch makes blkcg_[rw]stat per-cpu and drop the ad-hoc
per-cpu wrapping in blk-throttle.

* blkg_[rw]stat->cnt is replaced with cpu_cnt which is struct
  percpu_counter.  This makes syncp unnecessary as remote accesses are
  handled by percpu_counter itself.

* blkg_[rw]stat_init() can now fail due to percpu allocation failure
  and thus are updated to return int.

* percpu_counters need explicit freeing.  blkg_[rw]stat_exit() added.

* As blkg_rwstat->cpu_cnt[] can't be read directly anymore, reading
  and summing results are stored in ->aux_cnt[] instead.

* Custom per-cpu stat implementation in blk-throttle is removed.

This makes all blkcg stat counters per-cpu without complicating policy
implmentations.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index ff79b52..02a2d02 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -539,9 +539,10 @@ 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)rwstat->cnt[i]);
+                          (unsigned long long)atomic64_read(&rwstat->aux_cnt[i]));
 
-       v = rwstat->cnt[BLKG_RWSTAT_READ] + rwstat->cnt[BLKG_RWSTAT_WRITE];
+       v = atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_READ]) +
+               atomic64_read(&rwstat->aux_cnt[BLKG_RWSTAT_WRITE]);
        seq_printf(sf, "%s Total %llu\n", dname, (unsigned long long)v);
        return v;
 }
@@ -643,8 +644,9 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkg_policy_data *pd,
                tmp = blkg_rwstat_read(rwstat);
 
                for (i = 0; i < BLKG_RWSTAT_NR; i++)
-                       sum.cnt[i] += tmp.cnt[i] +
-                               atomic64_read(&rwstat->aux_cnt[i]);
+                       atomic64_add(atomic64_read(&tmp.aux_cnt[i]) +
+                                    atomic64_read(&rwstat->aux_cnt[i]),
+                                    &sum.aux_cnt[i]);
        }
        rcu_read_unlock();
 

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 29c22ed..c0b2263 100644 (file)
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -83,14 +83,6 @@ enum tg_state_flags {
 
 #define rb_entry_tg(node)      rb_entry((node), struct throtl_grp, rb_node)
 
-/* Per-cpu group stats */
-struct tg_stats_cpu {
-       /* total bytes transferred */
-       struct blkg_rwstat              service_bytes;
-       /* total IOs serviced, post merge */
-       struct blkg_rwstat              serviced;
-};
-
 struct throtl_grp {
        /* must be the first member */
        struct blkg_policy_data pd;
@@ -142,8 +134,10 @@ struct throtl_grp {
        unsigned long slice_start[2];
        unsigned long slice_end[2];
 
-       /* Per cpu stats pointer */
-       struct tg_stats_cpu __percpu *stats_cpu;
+       /* total bytes transferred */
+       struct blkg_rwstat              service_bytes;
+       /* total IOs serviced, post merge */
+       struct blkg_rwstat              serviced;
 };
 
 struct throtl_data
@@ -337,17 +331,15 @@ static void throtl_service_queue_init(struct throtl_service_queue *sq)
 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
 {
        struct throtl_grp *tg;
-       int rw, cpu;
+       int rw;
 
        tg = kzalloc_node(sizeof(*tg), gfp, node);
        if (!tg)
-               return NULL;
+               goto err;
 
-       tg->stats_cpu = alloc_percpu_gfp(struct tg_stats_cpu, gfp);
-       if (!tg->stats_cpu) {
-               kfree(tg);
-               return NULL;
-       }
+       if (blkg_rwstat_init(&tg->service_bytes, gfp) ||
+           blkg_rwstat_init(&tg->serviced, gfp))
+               goto err_free_tg;
 
        throtl_service_queue_init(&tg->service_queue);
 
@@ -362,14 +354,14 @@ static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
        tg->iops[READ] = -1;
        tg->iops[WRITE] = -1;
 
-       for_each_possible_cpu(cpu) {
-               struct tg_stats_cpu *stats_cpu = per_cpu_ptr(tg->stats_cpu, cpu);
-
-               blkg_rwstat_init(&stats_cpu->service_bytes);
-               blkg_rwstat_init(&stats_cpu->serviced);
-       }
-
        return &tg->pd;
+
+err_free_tg:
+       blkg_rwstat_exit(&tg->serviced);
+       blkg_rwstat_exit(&tg->service_bytes);
+       kfree(tg);
+err:
+       return NULL;
 }
 
 static void throtl_pd_init(struct blkg_policy_data *pd)
@@ -427,21 +419,17 @@ static void throtl_pd_free(struct blkg_policy_data *pd)
        struct throtl_grp *tg = pd_to_tg(pd);
 
        del_timer_sync(&tg->service_queue.pending_timer);
-       free_percpu(tg->stats_cpu);
+       blkg_rwstat_exit(&tg->serviced);
+       blkg_rwstat_exit(&tg->service_bytes);
        kfree(tg);
 }
 
 static void throtl_pd_reset_stats(struct blkg_policy_data *pd)
 {
        struct throtl_grp *tg = pd_to_tg(pd);
-       int cpu;
 
-       for_each_possible_cpu(cpu) {
-               struct tg_stats_cpu *sc = per_cpu_ptr(tg->stats_cpu, cpu);
-
-               blkg_rwstat_reset(&sc->service_bytes);
-               blkg_rwstat_reset(&sc->serviced);
-       }
+       blkg_rwstat_reset(&tg->service_bytes);
+       blkg_rwstat_reset(&tg->serviced);
 }
 
 static struct throtl_grp *
@@ -855,7 +843,6 @@ static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
                                         int rw)
 {
        struct throtl_grp *tg = blkg_to_tg(blkg);
-       struct tg_stats_cpu *stats_cpu;
        unsigned long flags;
 
        /*
@@ -865,10 +852,8 @@ static void throtl_update_dispatch_stats(struct blkcg_gq *blkg, u64 bytes,
         */
        local_irq_save(flags);
 
-       stats_cpu = this_cpu_ptr(tg->stats_cpu);
-
-       blkg_rwstat_add(&stats_cpu->serviced, rw, 1);
-       blkg_rwstat_add(&stats_cpu->service_bytes, rw, bytes);
+       blkg_rwstat_add(&tg->serviced, rw, 1);
+       blkg_rwstat_add(&tg->service_bytes, rw, bytes);
 
        local_irq_restore(flags);
 }
@@ -1176,27 +1161,9 @@ static void blk_throtl_dispatch_work_fn(struct work_struct *work)
        }
 }
 
-static u64 tg_prfill_cpu_rwstat(struct seq_file *sf,
-                               struct blkg_policy_data *pd, int off)
-{
-       struct throtl_grp *tg = pd_to_tg(pd);
-       struct blkg_rwstat rwstat = { }, tmp;
-       int i, cpu;
-
-       for_each_possible_cpu(cpu) {
-               struct tg_stats_cpu *sc = per_cpu_ptr(tg->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);
-}
-
-static int tg_print_cpu_rwstat(struct seq_file *sf, void *v)
+static int tg_print_rwstat(struct seq_file *sf, void *v)
 {
-       blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_cpu_rwstat,
+       blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), blkg_prfill_rwstat,
                          &blkcg_policy_throtl, seq_cft(sf)->private, true);
        return 0;
 }
@@ -1337,13 +1304,13 @@ static struct cftype throtl_files[] = {
        },
        {
                .name = "throttle.io_service_bytes",
-               .private = offsetof(struct tg_stats_cpu, service_bytes),
-               .seq_show = tg_print_cpu_rwstat,
+               .private = offsetof(struct throtl_grp, service_bytes),
+               .seq_show = tg_print_rwstat,
        },
        {
                .name = "throttle.io_serviced",
-               .private = offsetof(struct tg_stats_cpu, serviced),
-               .seq_show = tg_print_cpu_rwstat,
+               .private = offsetof(struct throtl_grp, serviced),
+               .seq_show = tg_print_rwstat,
        },
        { }     /* terminate */
 };

diff --cc block/cfq-iosched.c
Simple merge

diff --cc include/linux/blk-cgroup.h
Simple merge