Re: [PATCH v8 13/13] nvmet-passthru: support block accounting

[Sagi Grimberg]

> > > > > Support block disk accounting by setting the RQF_IO_STAT flag
> > > > > and gendisk in the request.
> > > > >
> > > > > After this change, IO counts will be reflected correctly in
> > > > > /proc/diskstats for drives being used by passthru.
> > > > >
> > > > > Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> > > > > ---
> > > > >     drivers/nvme/target/io-cmd-passthru.c | 5 ++++-
> > > > >     1 file changed, 4 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/nvme/target/io-cmd-passthru.c b/drivers/nvme/target/io-cmd-passthru.c
> > > > > index 7557927a3451..63f12750a80d 100644
> > > > > --- a/drivers/nvme/target/io-cmd-passthru.c
> > > > > +++ b/drivers/nvme/target/io-cmd-passthru.c
> > > > > @@ -410,6 +410,9 @@ static struct request *nvmet_passthru_blk_make_request(struct nvmet_req *req,
> > > > >     	if (unlikely(IS_ERR(rq)))
> > > > >     		return rq;
> > > > >     
> > > > > +	if (blk_queue_io_stat(q) && cmd->common.opcode != nvme_cmd_flush)
> > > > > +		rq->rq_flags |= RQF_IO_STAT;
> > >
> > > Thanks for the review!
> > >
> > > > Does flush has data bytes in the request? Why the special casing?
> > >
> > > Well it was special cased in the vanilla blk account flow... But I think
> > > it's required to be special cased so the IO and in_flight counts don't
> > > count flushes (as they do not for regular block device traffic).
> >
> > I think that the accounting exclude I/O that is yielded from the flush
> > sequence. Don't think its relevant here...
>
> What? Per blk_account_io_done(), RQF_FLUSH_SEQ will not be set by us for
> passthru commands and I don't think it's appropriate to do so. Thus, if
> we set RQF_IO_STAT for passthru flush commands, they will be counted
> which we do not want.

Have you considered to have nvmet_passthru_blk_make_request set RQF_FUA
for nvme_cmd_flush? this way blk_insert_flush will be called and
RQF_FLUSH_SEQ will be set and you don't need to worry about this
special casing...