On Tue, Nov 27 2018 at 7:42pm -0500, Mikulas Patocka <[email protected]> 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 <[email protected]> > > --- > 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); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
