Re: [PATCH 2/7] block: Implement support for WRITE SAME

["Martin K. Petersen" <martin.petersen@oracle.com>]

>>>>> "Vivek" == Vivek Goyal <vgoyal@redhat.com> writes:

Vivek> Thinking loud. Will it logically make sense to account for whole
Vivek> BIO (all the sectors and not just 1). Target device did the
Vivek> actual work of writing the sector. Just that we reduced the data
Vivek> transfer overhead.

We have absolutely no idea how much work the storage device will do. It
could be doing zero-detect or dedup causing it to update an internal
allocation map instead of actually writing out blocks. Or it could be
forced to do more I/O than we requested due to wear leveling or because
it is a RAID device which has to write out full stripes and parity
blocks.


Vivek> I thought it will make more sense to count WRITE_SAME towards
Vivek> number of sectors written and not DISCARDS. Not sure why it make
Vivek> sense to count discard sectors towards sectors written in
Vivek> disk/part stat.

But we're measuring page out activity, right?

In my mind the only thing we can reliably measure is the I/O we're
transmitting to or receiving from the device. So I'd personally like to
see zero for discard and logical block size for write same.

-- 
Martin K. Petersen	Oracle Linux Engineering