On 11/30/18 2:44 PM, Mike Snitzer wrote:
> 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:
Should also be using this_cpu_inc/dec instead.
--
Jens Axboe
