block: delete part_round_stats and switch to less precise counting

We want to convert to per-cpu in_flight counters.

The function part_round_stats needs the in_flight counter every jiffy, it
would be too costly to sum all the percpu variables every jiffy, so it
must be deleted. part_round_stats is used to calculate two counters -
time_in_queue and io_ticks.

time_in_queue can be calculated without part_round_stats, by adding the
duration of the I/O when the I/O ends (the value is almost as exact as the
previously calculated value, except that time for in-progress I/Os is not
counted).

io_ticks can be approximated by increasing the value when I/O is started
or ended and the jiffies value has changed. If the I/Os take less than a
jiffy, the value is as exact as the previously calculated value. If the
I/Os take more than a jiffy, io_ticks can drift behind the previously
calculated value.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index 0aca870331c394fa2684e6d9eabeb8d3b27d812e..036e3f0cc7364082b0db81bc145ee03b2a24f5fb 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1664,6 +1664,22 @@ defer:
 }
 EXPORT_SYMBOL_GPL(bio_check_pages_dirty);
 
+void update_io_ticks(struct hd_struct *part, unsigned long now)
+{
+       unsigned long stamp;
+again:
+       stamp = READ_ONCE(part->stamp);
+       if (unlikely(stamp != now)) {
+               if (likely(cmpxchg(&part->stamp, stamp, now) == stamp)) {
+                       __part_stat_add(part, io_ticks, 1);
+               }
+       }
+       if (part->partno) {
+               part = &part_to_disk(part)->part0;
+               goto again;
+       }
+}
+
 void generic_start_io_acct(struct request_queue *q, int op,
                           unsigned long sectors, struct hd_struct *part)
 {
@@ -1671,7 +1687,7 @@ void generic_start_io_acct(struct request_queue *q, int op,
 
        part_stat_lock();
 
-       part_round_stats(q, part);
+       update_io_ticks(part, jiffies);
        part_stat_inc(part, ios[sgrp]);
        part_stat_add(part, sectors[sgrp], sectors);
        part_inc_in_flight(q, part, op_is_write(op));
@@ -1683,13 +1699,15 @@ EXPORT_SYMBOL(generic_start_io_acct);
 void generic_end_io_acct(struct request_queue *q, int req_op,
                         struct hd_struct *part, unsigned long start_time)
 {
-       unsigned long duration = jiffies - start_time;
+       unsigned long now = jiffies;
+       unsigned long duration = now - start_time;
        const int sgrp = op_stat_group(req_op);
 
        part_stat_lock();
 
+       update_io_ticks(part, now);
        part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));
-       part_round_stats(q, part);
+       part_stat_add(part, time_in_queue, duration);
        part_dec_in_flight(q, part, op_is_write(req_op));
 
        part_stat_unlock();

diff --git a/block/blk-core.c b/block/blk-core.c
index 734b768c9d9d69d40390e09e26129acbf33fa655..268d2b8e984330d03a2e584f1d724478f285e3a6 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -584,62 +584,6 @@ struct request *blk_get_request(struct request_queue *q, unsigned int op,
 }
 EXPORT_SYMBOL(blk_get_request);
 
-static void part_round_stats_single(struct request_queue *q,
-                                   struct hd_struct *part, unsigned long now,
-                                   unsigned int inflight)
-{
-       if (inflight) {
-               __part_stat_add(part, time_in_queue,
-                               inflight * (now - part->stamp));
-               __part_stat_add(part, io_ticks, (now - part->stamp));
-       }
-       part->stamp = now;
-}
-
-/**
- * part_round_stats() - Round off the performance stats on a struct disk_stats.
- * @q: target block queue
- * @part: target partition
- *
- * The average IO queue length and utilisation statistics are maintained
- * by observing the current state of the queue length and the amount of
- * time it has been in this state for.
- *
- * Normally, that accounting is done on IO completion, but that can result
- * in more than a second's worth of IO being accounted for within any one
- * second, leading to >100% utilisation.  To deal with that, we call this
- * function to do a round-off before returning the results when reading
- * /proc/diskstats.  This accounts immediately for all queue usage up to
- * the current jiffies and restarts the counters again.
- */
-void part_round_stats(struct request_queue *q, struct hd_struct *part)
-{
-       struct hd_struct *part2 = NULL;
-       unsigned long now = jiffies;
-       unsigned int inflight[2];
-       int stats = 0;
-
-       if (part->stamp != now)
-               stats |= 1;
-
-       if (part->partno) {
-               part2 = &part_to_disk(part)->part0;
-               if (part2->stamp != now)
-                       stats |= 2;
-       }
-
-       if (!stats)
-               return;
-
-       part_in_flight(q, part, inflight);
-
-       if (stats & 2)
-               part_round_stats_single(q, part2, now, inflight[1]);
-       if (stats & 1)
-               part_round_stats_single(q, part, now, inflight[0]);
-}
-EXPORT_SYMBOL_GPL(part_round_stats);
-
 void blk_put_request(struct request *req)
 {
        blk_mq_free_request(req);
@@ -1383,9 +1327,10 @@ void blk_account_io_done(struct request *req, u64 now)
                part_stat_lock();
                part = req->part;
 
+               update_io_ticks(part, jiffies);
                part_stat_inc(part, ios[sgrp]);
                part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
-               part_round_stats(req->q, part);
+               part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
                part_dec_in_flight(req->q, part, rq_data_dir(req));
 
                hd_struct_put(part);
@@ -1420,11 +1365,12 @@ void blk_account_io_start(struct request *rq, bool new_io)
                        part = &rq->rq_disk->part0;
                        hd_struct_get(part);
                }
-               part_round_stats(rq->q, part);
                part_inc_in_flight(rq->q, part, rw);
                rq->part = part;
        }
 
+       update_io_ticks(part, jiffies);
+
        part_stat_unlock();
 }
 

diff --git a/block/blk-merge.c b/block/blk-merge.c
index a120d59b970552eba5889a594c853bfae0b83593..9da5629d08876e4cb780739eb35c351226ca8f81 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -689,7 +689,6 @@ static void blk_account_io_merge(struct request *req)
                part_stat_lock();
                part = req->part;
 
-               part_round_stats(req->q, part);
                part_dec_in_flight(req->q, part, rq_data_dir(req));
 
                hd_struct_put(part);

diff --git a/block/genhd.c b/block/genhd.c
index 2fe00cf32b93bae3145e33781f3286c6ea692c87..cdf174d7d3292747cd6a56af36815d27d24040aa 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1337,9 +1337,6 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 
        disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0);
        while ((hd = disk_part_iter_next(&piter))) {
-               part_stat_lock();
-               part_round_stats(gp->queue, hd);
-               part_stat_unlock();
                part_in_flight(gp->queue, hd, inflight);
                seq_printf(seqf, "%4d %7d %s "
                           "%lu %lu %lu %u "

diff --git a/block/partition-generic.c b/block/partition-generic.c
index 7e663cfb1487bcfbc061015ce201377b0324f828..42d6138ac87677d3ff1390cf28d0eac5bf5235a2 100644 (file)
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -122,9 +122,6 @@ ssize_t part_stat_show(struct device *dev,
        struct request_queue *q = part_to_disk(p)->queue;
        unsigned int inflight[2];
 
-       part_stat_lock();
-       part_round_stats(q, p);
-       part_stat_unlock();
        part_in_flight(q, p, inflight);
        return sprintf(buf,
                "%8lu %8lu %8llu %8u "

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 1677cd2a4c4e921493862c675a78035f37305076..838c2a7a40c523cec481f86530d32e9d30da38c0 100644 (file)
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -398,8 +398,7 @@ static inline void free_part_info(struct hd_struct *part)
        kfree(part->info);
 }
 
-/* block/blk-core.c */
-extern void part_round_stats(struct request_queue *q, struct hd_struct *part);
+void update_io_ticks(struct hd_struct *part, unsigned long now);
 
 /* block/genhd.c */
 extern void device_add_disk(struct device *parent, struct gendisk *disk,