[dm-devel] ios and sectors should be incremented on completion

[Junichi Nomura]

On 09/26/14 18:12, Akira Hayakawa wrote:
> I seems DM increments stats (ios and sectors) before completion.
> Why don't you do this in dec_pending?
> block/stat.txt says these values are incremented when I/O request completes.
> 
> Is this to be fixed or do you have some justifications for this behavior?

Do you have a problem with the current behavior other than the document?

AFAIR, dm increments ios/sectors at submission because md did.
And other bio-based drivers such as drbd and nvme seem to have followed
the precedence.

While md has a reason to do so (some md personalities just remaps bios
and doesn't track completion), dm should be able to collect stat
in dec_pending as it always clones.

So, I think it's ok to move ios/sectors counting to end_io_acct().
It might make tools like iostat happier.
You might want to fix other bio-based drivers as well.

-- 
Jun'ichi Nomura, NEC Corporation