On Tue, Nov 27 2018 at 7:42pm -0500,
Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>
> ---
> block/bio.c | 26 ++++++++++++++++--
> block/blk-core.c | 64 +++-------------------------------------------
> block/blk-merge.c | 1
> block/genhd.c | 4 --
> block/partition-generic.c | 4 --
> include/linux/genhd.h | 3 --
> 6 files changed, 29 insertions(+), 73 deletions(-)
>
> Index: linux-block/block/bio.c
> ===================================================================
> --- linux-block.orig/block/bio.c 2018-11-26 23:44:17.000000000 +0100
> +++ linux-block/block/bio.c 2018-11-26 23:44:17.000000000 +0100
> @@ -1663,13 +1663,29 @@ defer:
> }
> EXPORT_SYMBOL_GPL(bio_check_pages_dirty);
>
> +void update_io_ticks(int cpu, 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(cpu, 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)
> {
> const int sgrp = op_stat_group(op);
> int cpu = part_stat_lock();
>
> - part_round_stats(q, cpu, part);
> + update_io_ticks(cpu, part, jiffies);
> part_stat_inc(cpu, part, ios[sgrp]);
> part_stat_add(cpu, part, sectors[sgrp], sectors);
> part_inc_in_flight(q, part, op_is_write(op));
> @@ -1681,12 +1697,16 @@ 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);
> int cpu = part_stat_lock();
>
> + update_io_ticks(cpu, part, now);
> part_stat_add(cpu, part, nsecs[sgrp], jiffies_to_nsecs(duration));
> - part_round_stats(q, cpu, part);
> + part_stat_add(cpu, part, time_in_queue, duration);
> + if (part->partno)
> + part_stat_add(cpu, &part_to_disk(part)->part0, time_in_queue, duration);
> part_dec_in_flight(q, part, op_is_write(req_op));
>
> part_stat_unlock();
> Index: linux-block/block/blk-core.c
> ===================================================================
> --- linux-block.orig/block/blk-core.c 2018-11-26 23:44:17.000000000 +0100
> +++ linux-block/block/blk-core.c 2018-11-26 23:44:17.000000000 +0100
> @@ -583,63 +583,6 @@ struct request *blk_get_request(struct r
> }
> EXPORT_SYMBOL(blk_get_request);
>
> -static void part_round_stats_single(struct request_queue *q, int cpu,
> - struct hd_struct *part, unsigned long now,
> - unsigned int inflight)
> -{
> - if (inflight) {
> - __part_stat_add(cpu, part, time_in_queue,
> - inflight * (now - part->stamp));
> - __part_stat_add(cpu, 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
> - * @cpu: cpu number for stats access
> - * @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, int cpu, 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, cpu, part2, now, inflight[1]);
> - if (stats & 1)
> - part_round_stats_single(q, cpu, part, now, inflight[0]);
> -}
> -EXPORT_SYMBOL_GPL(part_round_stats);
> -
> void blk_put_request(struct request *req)
> {
> blk_mq_free_request(req);
> @@ -1408,9 +1351,11 @@ void blk_account_io_done(struct request
> cpu = part_stat_lock();
> part = req->part;
>
> + update_io_ticks(cpu, part, jiffies);
> part_stat_inc(cpu, part, ios[sgrp]);
> part_stat_add(cpu, part, nsecs[sgrp], now - req->start_time_ns);
> - part_round_stats(req->q, cpu, part);
> + part_stat_add(cpu, part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
(Extra indentation offered a clue...)
Are you missing an 'if (part->partno)' conditional here?
> + part_stat_add(cpu, &part_to_disk(part)->part0, 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);
