On 4/10/25 3:24 AM, Christoph Hellwig wrote: > On Tue, Apr 08, 2025 at 08:49:54PM -0600, Caleb Sander Mateos wrote: >> The ublk driver calls blk_mq_tag_to_rq() in several places. >> blk_mq_tag_to_rq() tolerates an invalid tag for the tagset, checking it >> against the number of tags and returning NULL if it is out of bounds. >> But all the calls from the ublk driver have already verified the tag >> against the ublk queue's queue depth. In ublk_commit_completion(), >> ublk_handle_need_get_data(), and case UBLK_IO_COMMIT_AND_FETCH_REQ, the >> tag has already been checked in __ublk_ch_uring_cmd(). In >> ublk_abort_queue(), the loop bounds the tag by the queue depth. In >> __ublk_check_and_get_req(), the tag has already been checked in >> __ublk_ch_uring_cmd(), in the case of ublk_register_io_buf(), or in >> ublk_check_and_get_req(). >> >> So just index the tagset's rqs array directly in the ublk driver. >> Convert the tags to unsigned, as blk_mq_tag_to_rq() does. > > Poking directly into block layer internals feels like a really bad > idea. If this is important enough we'll need a non-checking helper > in the core code, but as with all these kinds of micro-optimizations > it better have a really good justification. FWIW, I agree, and I also have a hard time imagining this making much of a measurable difference. Caleb, was this based "well this seems pointless" or was it something you noticed in profiling/testing? -- Jens Axboe
