The traditional single queue block device has no problem. Following is
the output when I writes to sda3 on version v3.10.
$cat /sys/block/sda/sda3/inflight
0 33
$cat /sys/block/sda/inflight
0 33
On the other hand, we can analyze this from the code. Following code
path for single-queue block device is from v4.19.
1. When reading '/sys/block/sda/inflight', the statistics is actually
fetched from part 0.
part_inflight_show
part_in_flight_rw
inflight[0] = atomic_read(&part->in_flight[0]);
inflight[1] = atomic_read(&part->in_flight[1]);
2. part 0 will always be updated whenever sub partition is updated.
blk_queue_bio
add_acct_request
blk_account_io_start
part_inc_in_flight
atomic_inc(&part->in_flight[rw])
if (part->partno)
atomic_inc(part0.in_flight[rw]);
On 12/1/20 1:05 AM, Christoph Hellwig wrote:
> On Thu, Nov 26, 2020 at 05:48:33PM +0800, Jeffle Xu wrote:
>> The inflight of partition 0 doesn't include inflight IOs to all
>> sub-partitions, since currently mq calculates inflight of specific
>> partition by simply camparing the value of the partition pointer.
>>
>> Thus the following case is possible:
>>
>> $ cat /sys/block/vda/inflight
>> ?? ?? ?? ??0 ?? ?? ?? ??0
>> $ cat /sys/block/vda/vda1/inflight
>> ?? ?? ?? ??0 ?? ?? ??128
>>
>> Partition 0 should be specially handled since it represents the whole
>> disk.
>
> I'm not sure and can see arguments for either side. In doubt we should
> stick to historic behavior, can you check what old kernels (especially
> before blk-mq) did?
>
--
Thanks,
Jeffle
