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

From: Sagi Grimberg
Date: Mon Sep 09 2019 - 19:15:31 EST

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...