| Message ID | 20181128004249.147084927@debian.vm (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | per-cpu in_flight counters for bio-based drivers | expand |
On Tue, Nov 27 2018 at 7:42pm -0500, Mikulas Patocka <mpatocka@redhat.com> 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@redhat.com> > > --- > 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);
On Fri, Nov 30 2018 at 2:42pm -0500, Mike Snitzer <snitzer@redhat.com> wrote: > On Tue, Nov 27 2018 at 7:42pm -0500, > Mikulas Patocka <mpatocka@redhat.com> 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@redhat.com> > > > > --- > > 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); > part_stat_add() already deals with the 'if (part->partno)' case. So you were double accounting -- here and in generic_end_io_acct()
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)); + 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); @@ -1446,11 +1391,12 @@ void blk_account_io_start(struct request part = &rq->rq_disk->part0; hd_struct_get(part); } - part_round_stats(rq->q, cpu, part); part_inc_in_flight(rq->q, part, rw); rq->part = part; } + update_io_ticks(cpu, part, jiffies); + part_stat_unlock(); } Index: linux-block/block/blk-merge.c =================================================================== --- linux-block.orig/block/blk-merge.c 2018-11-26 23:44:17.000000000 +0100 +++ linux-block/block/blk-merge.c 2018-11-26 23:44:17.000000000 +0100 @@ -690,7 +690,6 @@ static void blk_account_io_merge(struct cpu = part_stat_lock(); part = req->part; - part_round_stats(req->q, cpu, part); part_dec_in_flight(req->q, part, rq_data_dir(req)); hd_struct_put(part); Index: linux-block/block/genhd.c =================================================================== --- linux-block.orig/block/genhd.c 2018-11-26 23:44:17.000000000 +0100 +++ linux-block/block/genhd.c 2018-11-26 23:44:17.000000000 +0100 @@ -1326,7 +1326,6 @@ static int diskstats_show(struct seq_fil struct hd_struct *hd; char buf[BDEVNAME_SIZE]; unsigned int inflight[2]; - int cpu; /* if (&disk_to_dev(gp)->kobj.entry == block_class.devices.next) @@ -1338,9 +1337,6 @@ static int diskstats_show(struct seq_fil disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0); while ((hd = disk_part_iter_next(&piter))) { - cpu = part_stat_lock(); - part_round_stats(gp->queue, cpu, hd); - part_stat_unlock(); part_in_flight(gp->queue, hd, inflight); seq_printf(seqf, "%4d %7d %s " "%lu %lu %lu %u " Index: linux-block/block/partition-generic.c =================================================================== --- linux-block.orig/block/partition-generic.c 2018-11-26 23:44:17.000000000 +0100 +++ linux-block/block/partition-generic.c 2018-11-26 23:44:17.000000000 +0100 @@ -121,11 +121,7 @@ ssize_t part_stat_show(struct device *de struct hd_struct *p = dev_to_part(dev); struct request_queue *q = part_to_disk(p)->queue; unsigned int inflight[2]; - int cpu; - cpu = part_stat_lock(); - part_round_stats(q, cpu, p); - part_stat_unlock(); part_in_flight(q, p, inflight); return sprintf(buf, "%8lu %8lu %8llu %8u " Index: linux-block/include/linux/genhd.h =================================================================== --- linux-block.orig/include/linux/genhd.h 2018-11-26 23:44:17.000000000 +0100 +++ linux-block/include/linux/genhd.h 2018-11-26 23:44:17.000000000 +0100 @@ -398,8 +398,7 @@ static inline void free_part_info(struct kfree(part->info); } -/* block/blk-core.c */ -extern void part_round_stats(struct request_queue *q, int cpu, struct hd_struct *part); +void update_io_ticks(int cpu, struct hd_struct *part, unsigned long now); /* block/genhd.c */ extern void device_add_disk(struct device *parent, struct gendisk *disk,
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> --- 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(-)