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blkcg: make blkcg_[rw]stat per-cpu

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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 <[email protected]>
Cc: Vivek Goyal <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Tejun Heo 2015-08-18 14:55:22 -07:00 • committed by Jens Axboe
commit 24bdb8ef06
4 changed files with 153 additions and 136 deletions
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89
block/blk-throttle.c
View file

@ -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)
static int tg_print_rwstat(struct seq_file *sf, void *v)
{
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)
{
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 */
};