blk-stat: delete useless code

Fix two issues:
- the per-cpu stat flush is unnecessary, nobody uses per-cpu stat except
  sum it to global stat. We can do the calculation there. The flush just
  wastes cpu time.
- some fields are signed int/s64. I don't see the point.

Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-stat.c b/block/blk-stat.c
index c52356d90fe3854f05faebda241707a1b112a543..3a2f3c96f3672e102d0498848e6086d9ad7184f8 100644 (file)
--- a/block/blk-stat.c
+++ b/block/blk-stat.c
@@ -11,8 +11,6 @@
 #include "blk-mq.h"
 #include "blk.h"
 
-#define BLK_RQ_STAT_BATCH      64
-
 struct blk_queue_stats {
        struct list_head callbacks;
        spinlock_t lock;
@@ -23,45 +21,21 @@ static void blk_stat_init(struct blk_rq_stat *stat)
 {
        stat->min = -1ULL;
        stat->max = stat->nr_samples = stat->mean = 0;
-       stat->batch = stat->nr_batch = 0;
-}
-
-static void blk_stat_flush_batch(struct blk_rq_stat *stat)
-{
-       const s32 nr_batch = READ_ONCE(stat->nr_batch);
-       const s32 nr_samples = READ_ONCE(stat->nr_samples);
-
-       if (!nr_batch)
-               return;
-       if (!nr_samples)
-               stat->mean = div64_s64(stat->batch, nr_batch);
-       else {
-               stat->mean = div64_s64((stat->mean * nr_samples) +
-                                       stat->batch,
-                                       nr_batch + nr_samples);
-       }
-
-       stat->nr_samples += nr_batch;
-       stat->nr_batch = stat->batch = 0;
+       stat->batch = 0;
 }
 
+/* src is a per-cpu stat, mean isn't initialized */
 static void blk_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
 {
-       blk_stat_flush_batch(src);
-
        if (!src->nr_samples)
                return;
 
        dst->min = min(dst->min, src->min);
        dst->max = max(dst->max, src->max);
 
-       if (!dst->nr_samples)
-               dst->mean = src->mean;
-       else {
-               dst->mean = div64_s64((src->mean * src->nr_samples) +
-                                       (dst->mean * dst->nr_samples),
-                                       dst->nr_samples + src->nr_samples);
-       }
+       dst->mean = div_u64(src->batch + dst->mean * dst->nr_samples,
+                               dst->nr_samples + src->nr_samples);
+
        dst->nr_samples += src->nr_samples;
 }
 
@@ -69,13 +43,8 @@ static void __blk_stat_add(struct blk_rq_stat *stat, u64 value)
 {
        stat->min = min(stat->min, value);
        stat->max = max(stat->max, value);
-
-       if (stat->batch + value < stat->batch ||
-           stat->nr_batch + 1 == BLK_RQ_STAT_BATCH)
-               blk_stat_flush_batch(stat);
-
        stat->batch += value;
-       stat->nr_batch++;
+       stat->nr_samples++;
 }
 
 void blk_stat_add(struct request *rq)
@@ -84,7 +53,7 @@ void blk_stat_add(struct request *rq)
        struct blk_stat_callback *cb;
        struct blk_rq_stat *stat;
        int bucket;
-       s64 now, value;
+       u64 now, value;
 
        now = __blk_stat_time(ktime_to_ns(ktime_get()));
        if (now < blk_stat_time(&rq->issue_stat))

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index a2d2aa709cef4afc0bb5c3875df3073b81b368fa..3385c89f402e2556c76c69d695dc3caf4a9f80ea 100644 (file)
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -329,11 +329,10 @@ static inline bool blk_qc_t_is_internal(blk_qc_t cookie)
 }
 
 struct blk_rq_stat {
-       s64 mean;
+       u64 mean;
        u64 min;
        u64 max;
-       s32 nr_samples;
-       s32 nr_batch;
+       u32 nr_samples;
        u64 batch;
 };