Commits
Jens Axboe committed f906a6a0f42
blk-mq: improve tag waiting setup for non-shared tags If we run out of driver tags, we currently treat shared and non-shared tags the same - both cases hook into the tag waitqueue. This is a bit more costly than it needs to be on unshared tags, since we have to both grab the hctx lock, and the waitqueue lock (and disable interrupts). For the non-shared case, we can simply mark the queue as needing a restart. Split blk_mq_dispatch_wait_add() to account for both cases, and rename it to blk_mq_mark_tag_wait() to better reflect what it does now. Without this patch, shared and non-shared performance is about the same with 4 fio thread hammering on a single null_blk device (~410K, at 75% sys). With the patch, the shared case is the same, but the non-shared tags case runs at 431K at 71% sys. Reviewed-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>