On Mon, Jun 20, 2022 at 06:02:30PM +0900, Damien Le Moal wrote: > So reserving a tag/req to be able to do NCQ at the cost of max qd being 31 > works for that. We could keep max qd at 32 by creating one more "fake" tag > and having a request for it, that is, having the fake tag visible to the > block layer as a reserved tag, as John's series is doing, but for the > reserved tags, we actually need to use an effective tag (qc->hw_tag) when > issuing the commands. And for that, we can reuse the tag of one of the > failed commands. Take a look at the magic flush request in blk-flush.c, which is preallocated but borrows a tag from the request that wants a pre- or post-flush. The logic is rather ugly, but maybe it might actually become cleaner by generalizing it a bit.
