On Wed, May 30, 2018 at 5:20 PM, jianchao.wang <jianchao.w.wang@xxxxxxxxxx> wrote: > Hi ming > > On 05/30/2018 05:13 PM, Ming Lei wrote: >>> Yes, it maybe good for merging of 'none', because the rq_list is split into 3 >>> lists, and not need to iterate the whole rq_list any more. >>> But what's about the dispatch when there is no io scheduler. >> blk_mq_flush_busy_ctxs() and blk_mq_dequeue_from_ctx() should work >> fine in case of 'none' if per-domain list is added to ctx. Then we can make >> none to be a bit fair on READ/WRITE. >> > > But how to determine when to dispatch READ, WRITE or other more, when there is no io scheduler ? > For blk-mq, no io scheduler means 'none' actually, and it works like a scheduler too, but just shares driver tags, IMO. Wrt. the current code of 'none', blk-mq just picks up one request from ctx->rq_list directly in FIFO style. If READ/WRITE lists are introduced, only blk_mq_dequeue_from_ctx() is effected, there are several choices left for us: 1) keep the FIFO style of current behaviour by using req->start_time_ns 2) READ/WRIRE fair style by picking up request from the lists in round-robin order 3) or others It just will make more choices for us, :-) Thanks, Ming Lei
