On Tue, Nov 27 2018 at 7:42pm -0500,
Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> Now when part_round_stats is gone, we can switch to per-cpu in-flight
> counters.
>
> We use the local-atomic type local_t, so that if part_inc_in_flight or
> part_dec_in_flight is reentrantly called from an interrupt, the value will
> be correct.
>
> The other counters could be corrupted due to reentrant interrupt, but the
> corruption only results in slight counter skew - the in_flight counter
> must be exact, so it needs local_t.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> ---
> block/bio.c | 4 ++--
> block/blk-core.c | 4 ++--
> block/blk-merge.c | 2 +-
> block/genhd.c | 47 +++++++++++++++++++++++++++++++++++------------
> drivers/md/dm.c | 4 +---
> include/linux/genhd.h | 7 ++++---
> 6 files changed, 45 insertions(+), 23 deletions(-)
>
> Index: linux-block/block/genhd.c
> ===================================================================
> --- linux-block.orig/block/genhd.c 2018-11-28 00:09:59.000000000 +0100
> +++ linux-block/block/genhd.c 2018-11-28 00:09:59.000000000 +0100
> @@ -45,53 +45,76 @@ static void disk_add_events(struct gendi
> static void disk_del_events(struct gendisk *disk);
> static void disk_release_events(struct gendisk *disk);
>
> -void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
> +void part_inc_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw)
> {
> if (queue_is_mq(q))
> return;
>
> - atomic_inc(&part->in_flight[rw]);
> + local_inc(per_cpu_ptr(part->dkstats, cpu)->in_flight);
> if (part->partno)
> - atomic_inc(&part_to_disk(part)->part0.in_flight[rw]);
> + local_inc(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight);
> }
>
> -void part_dec_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
> +void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw)
> {
> if (queue_is_mq(q))
> return;
>
> - atomic_dec(&part->in_flight[rw]);
> + local_dec(per_cpu_ptr(part->dkstats, cpu)->in_flight);
> if (part->partno)
> - atomic_dec(&part_to_disk(part)->part0.in_flight[rw]);
> + local_dec(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight);
> }
The above is wrong, needs this incremental fix:
diff --git a/block/genhd.c b/block/genhd.c
index 2ed431098953..3397288a2926 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -50,9 +50,9 @@ void part_inc_in_flight(struct request_queue *q, int cpu, struct hd_struct *part
if (queue_is_mq(q))
return;
- local_inc(per_cpu_ptr(part->dkstats, cpu)->in_flight);
+ local_inc(&per_cpu_ptr(part->dkstats, cpu)->in_flight[rw]);
if (part->partno)
- local_inc(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight);
+ local_inc(&per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight[rw]);
}
void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part, int rw)
@@ -60,9 +60,9 @@ void part_dec_in_flight(struct request_queue *q, int cpu, struct hd_struct *part
if (queue_is_mq(q))
return;
- local_dec(per_cpu_ptr(part->dkstats, cpu)->in_flight);
+ local_dec(&per_cpu_ptr(part->dkstats, cpu)->in_flight[rw]);
if (part->partno)
- local_dec(per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight);
+ local_dec(&per_cpu_ptr(part_to_disk(part)->part0.dkstats, cpu)->in_flight[rw]);
}
unsigned int part_in_flight(struct request_queue *q, struct hd_struct *part)
--
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