From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 29 May 2001 12:59:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 29 May 2001 12:59:02 -0400 Received: from zeus.kernel.org ([209.10.41.242]:47020 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id ; Tue, 29 May 2001 12:58:52 -0400 Date: Tue, 29 May 2001 18:04:29 +0200 From: Jens Axboe To: Linux Kernel Subject: [patch] I/O scheduler starvation Message-ID: <20010529180429.A504@suse.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="iVCmgExH7+hIHJ1A" Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --iVCmgExH7+hIHJ1A Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi, Going over this a bit, an deviant from the original design of elevator_linus seems to have snuck in. Well, almost, I've been aware of this for some time... The idea was _not_ to account request merges, since they will (in by far the most cases) incur the cost of a seek. Instead we just account seeks, any seek (and please don't start a debate on short vs long seeks again, I'm not listening). The attached patch corrects this, and also corrects the initial sequence numbers (typically this would be sequence / 8 number of seeks allowed to pass a request now). I'll do some formal timing on this later. -- Jens Axboe --iVCmgExH7+hIHJ1A Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=elv-starv-245-1 --- drivers/block/ll_rw_blk.c~ Tue May 29 17:53:58 2001 +++ drivers/block/ll_rw_blk.c Tue May 29 17:54:38 2001 @@ -742,7 +742,6 @@ case ELEVATOR_BACK_MERGE: if (!q->back_merge_fn(q, req, bh, max_segments)) break; - elevator->elevator_merge_cleanup_fn(q, req, count); req->bhtail->b_reqnext = bh; req->bhtail = bh; req->nr_sectors = req->hard_nr_sectors += count; @@ -754,7 +753,6 @@ case ELEVATOR_FRONT_MERGE: if (!q->front_merge_fn(q, req, bh, max_segments)) break; - elevator->elevator_merge_cleanup_fn(q, req, count); bh->b_reqnext = req->bh; req->bh = bh; req->buffer = bh->b_data; @@ -775,8 +773,10 @@ * request. if no hints, just add it to the back * of the queue */ - if (req) + if (req) { insert_here = &req->queue; + elevator->elevator_merge_cleanup_fn(q, req, count); + } break; default: --- drivers/block/elevator.c~ Tue May 29 17:54:03 2001 +++ drivers/block/elevator.c Tue May 29 17:59:28 2001 @@ -110,7 +110,6 @@ break; } else if (__rq->sector - count == bh->b_rsector) { ret = ELEVATOR_FRONT_MERGE; - __rq->elevator_sequence -= count; *req = __rq; break; } @@ -126,10 +125,10 @@ /* * second pass scan of requests that got passed over, if any */ - while ((entry = entry->next) != head) { + do { struct request *tmp = blkdev_entry_to_request(entry); tmp->elevator_sequence -= count; - } + } while ((entry = entry->next) != head); } void elevator_linus_merge_req(struct request *req, struct request *next) --- include/linux/elevator.h~ Tue May 29 17:54:10 2001 +++ include/linux/elevator.h Tue May 29 17:55:25 2001 @@ -93,8 +93,8 @@ #define ELEVATOR_LINUS \ ((elevator_t) { \ - 8192, /* read passovers */ \ - 16384, /* write passovers */ \ + 1024, /* read passovers */ \ + 4096, /* write passovers */ \ \ elevator_linus_merge, /* elevator_merge_fn */ \ elevator_linus_merge_cleanup, /* elevator_merge_cleanup_fn */ \ --iVCmgExH7+hIHJ1A--