Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 20 Dec 2001 13:20:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 20 Dec 2001 13:20:51 -0500 Received: from vasquez.zip.com.au ([203.12.97.41]:14853 "EHLO vasquez.zip.com.au") by vger.kernel.org with ESMTP id ; Thu, 20 Dec 2001 13:20:38 -0500 Message-ID: <3C222BB5.B2CCC11B@zip.com.au> Date: Thu, 20 Dec 2001 10:19:33 -0800 From: Andrew Morton X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.4.17-pre8 i686) X-Accept-Language: en MIME-Version: 1.0 To: William Lee Irwin III CC: Linux Kernel List Subject: Re: Poor performance during disk writes In-Reply-To: <20011220132729Z286241-18285+3296@vger.kernel.org>, <20011220132729Z286241-18285+3296@vger.kernel.org>; from Dieter.Nuetzel@hamburg.de on Thu, Dec 20, 2001 at 02:27:17PM +0100 <20011220094025.B2632@holomorphy.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org William Lee Irwin III wrote: > > Andrew, I don't have the URL for that still floating around. Can you > point Dieter to it? It's here. You need to run elvtune -b N /dev/hdXX where N=0 is "disable", N=1 is minimum read latency, N=6 is a reasonable setting. --- linux-2.4.17-pre6/drivers/block/elevator.c Thu Jul 19 20:59:41 2001 +++ linux-akpm/drivers/block/elevator.c Sat Dec 8 11:10:36 2001 @@ -74,11 +74,10 @@ inline int bh_rq_in_between(struct buffe return 0; } - int elevator_linus_merge(request_queue_t *q, struct request **req, struct list_head * head, struct buffer_head *bh, int rw, - int max_sectors) + int max_sectors, int max_bomb_segments) { struct list_head *entry = &q->queue_head; unsigned int count = bh->b_size >> 9, ret = ELEVATOR_NO_MERGE; @@ -116,6 +115,56 @@ int elevator_linus_merge(request_queue_t } } + /* + * If we failed to merge a read anywhere in the request + * queue, we really don't want to place it at the end + * of the list, behind lots of writes. So place it near + * the front. + * + * We don't want to place it in front of _all_ writes: that + * would create lots of seeking, and isn't tunable. + * We try to avoid promoting this read in front of existing + * reads. + * + * max_bomb_sectors becomes the maximum number of write + * requests which we allow to remain in place in front of + * a newly introduced read. We weight things a little bit, + * so large writes are more expensive than small ones, but it's + * requests which count, not sectors. + */ + if (max_bomb_segments && rw == READ && ret == ELEVATOR_NO_MERGE) { + int cur_latency = 0; + struct request * const cur_request = *req; + + entry = head->next; + while (entry != &q->queue_head) { + struct request *__rq; + + if (entry == &q->queue_head) + BUG(); + if (entry == q->queue_head.next && + q->head_active && !q->plugged) + BUG(); + __rq = blkdev_entry_to_request(entry); + + if (__rq == cur_request) { + /* + * This is where the old algorithm placed it. + * There's no point pushing it further back, + * so leave it here, in sorted order. + */ + break; + } + if (__rq->cmd == WRITE) { + cur_latency += 1 + __rq->nr_sectors / 64; + if (cur_latency >= max_bomb_segments) { + *req = __rq; + break; + } + } + entry = entry->next; + } + } return ret; } @@ -144,7 +193,7 @@ void elevator_linus_merge_req(struct req int elevator_noop_merge(request_queue_t *q, struct request **req, struct list_head * head, struct buffer_head *bh, int rw, - int max_sectors) + int max_sectors, int max_bomb_segments) { struct list_head *entry; unsigned int count = bh->b_size >> 9; @@ -188,7 +237,7 @@ int blkelvget_ioctl(elevator_t * elevato output.queue_ID = elevator->queue_ID; output.read_latency = elevator->read_latency; output.write_latency = elevator->write_latency; - output.max_bomb_segments = 0; + output.max_bomb_segments = elevator->max_bomb_segments; if (copy_to_user(arg, &output, sizeof(blkelv_ioctl_arg_t))) return -EFAULT; @@ -207,9 +256,12 @@ int blkelvset_ioctl(elevator_t * elevato return -EINVAL; if (input.write_latency < 0) return -EINVAL; + if (input.max_bomb_segments < 0) + return -EINVAL; elevator->read_latency = input.read_latency; elevator->write_latency = input.write_latency; + elevator->max_bomb_segments = input.max_bomb_segments; return 0; } --- linux-2.4.17-pre6/drivers/block/ll_rw_blk.c Mon Nov 5 21:01:11 2001 +++ linux-akpm/drivers/block/ll_rw_blk.c Sat Dec 8 11:10:36 2001 @@ -690,7 +690,8 @@ again: } else if (q->head_active && !q->plugged) head = head->next; - el_ret = elevator->elevator_merge_fn(q, &req, head, bh, rw,max_sectors); + el_ret = elevator->elevator_merge_fn(q, &req, head, bh, + rw, max_sectors, elevator->max_bomb_segments); switch (el_ret) { case ELEVATOR_BACK_MERGE: --- linux-2.4.17-pre6/include/linux/elevator.h Thu Feb 15 16:58:34 2001 +++ linux-akpm/include/linux/elevator.h Sat Dec 8 11:10:36 2001 @@ -5,8 +5,9 @@ typedef void (elevator_fn) (struct reque struct list_head *, struct list_head *, int); -typedef int (elevator_merge_fn) (request_queue_t *, struct request **, struct list_head *, - struct buffer_head *, int, int); +typedef int (elevator_merge_fn)(request_queue_t *, struct request **, + struct list_head *, struct buffer_head *bh, + int rw, int max_sectors, int max_bomb_segments); typedef void (elevator_merge_cleanup_fn) (request_queue_t *, struct request *, int); @@ -16,6 +17,7 @@ struct elevator_s { int read_latency; int write_latency; + int max_bomb_segments; elevator_merge_fn *elevator_merge_fn; elevator_merge_cleanup_fn *elevator_merge_cleanup_fn; @@ -24,13 +26,13 @@ struct elevator_s unsigned int queue_ID; }; -int elevator_noop_merge(request_queue_t *, struct request **, struct list_head *, struct buffer_head *, int, int); -void elevator_noop_merge_cleanup(request_queue_t *, struct request *, int); -void elevator_noop_merge_req(struct request *, struct request *); - -int elevator_linus_merge(request_queue_t *, struct request **, struct list_head *, struct buffer_head *, int, int); -void elevator_linus_merge_cleanup(request_queue_t *, struct request *, int); -void elevator_linus_merge_req(struct request *, struct request *); +elevator_merge_fn elevator_noop_merge; +elevator_merge_cleanup_fn elevator_noop_merge_cleanup; +elevator_merge_req_fn elevator_noop_merge_req; + +elevator_merge_fn elevator_linus_merge; +elevator_merge_cleanup_fn elevator_linus_merge_cleanup; +elevator_merge_req_fn elevator_linus_merge_req; typedef struct blkelv_ioctl_arg_s { int queue_ID; @@ -54,22 +56,6 @@ extern void elevator_init(elevator_t *, #define ELEVATOR_FRONT_MERGE 1 #define ELEVATOR_BACK_MERGE 2 -/* - * This is used in the elevator algorithm. We don't prioritise reads - * over writes any more --- although reads are more time-critical than - * writes, by treating them equally we increase filesystem throughput. - * This turns out to give better overall performance. -- sct - */ -#define IN_ORDER(s1,s2) \ - ((((s1)->rq_dev == (s2)->rq_dev && \ - (s1)->sector < (s2)->sector)) || \ - (s1)->rq_dev < (s2)->rq_dev) - -#define BHRQ_IN_ORDER(bh, rq) \ - ((((bh)->b_rdev == (rq)->rq_dev && \ - (bh)->b_rsector < (rq)->sector)) || \ - (bh)->b_rdev < (rq)->rq_dev) - static inline int elevator_request_latency(elevator_t * elevator, int rw) { int latency; @@ -85,7 +71,7 @@ static inline int elevator_request_laten ((elevator_t) { \ 0, /* read_latency */ \ 0, /* write_latency */ \ - \ + 0, /* max_bomb_segments */ \ elevator_noop_merge, /* elevator_merge_fn */ \ elevator_noop_merge_cleanup, /* elevator_merge_cleanup_fn */ \ elevator_noop_merge_req, /* elevator_merge_req_fn */ \ @@ -95,7 +81,7 @@ static inline int elevator_request_laten ((elevator_t) { \ 8192, /* read passovers */ \ 16384, /* write passovers */ \ - \ + 0, /* max_bomb_segments */ \ elevator_linus_merge, /* elevator_merge_fn */ \ elevator_linus_merge_cleanup, /* elevator_merge_cleanup_fn */ \ elevator_linus_merge_req, /* elevator_merge_req_fn */ \ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/