* [PATCH 1/3] deadline-iosched: allow non-sequential batching
2008-08-14 8:17 [PATCH 0/3] deadline-iosched: performance, style and documentation changes Aaron Carroll
@ 2008-08-14 8:17 ` Aaron Carroll
2008-08-14 8:17 ` [PATCH 2/3] deadline-iosched: non-functional fixes Aaron Carroll
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Aaron Carroll @ 2008-08-14 8:17 UTC (permalink / raw)
To: jens.axboe; +Cc: linux-kernel
Deadline currently only batches sector-contiguous requests, so except
for a few circumstances (e.g. requests in a single direction), it is
essentially first come first served. This is bad for throughput, so
change it to CSCAN, which means requests in a batch do not need to be
sequential and are issued in increasing sector order.
Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
---
block/deadline-iosched.c | 14 +++-----------
1 files changed, 3 insertions(+), 11 deletions(-)
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 342448c..07b80e4 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -258,17 +258,9 @@ static int deadline_dispatch_requests(struct request_queue *q, int force)
else
rq = dd->next_rq[READ];
- if (rq) {
- /* we have a "next request" */
-
- if (dd->last_sector != rq->sector)
- /* end the batch on a non sequential request */
- dd->batching += dd->fifo_batch;
-
- if (dd->batching < dd->fifo_batch)
- /* we are still entitled to batch */
- goto dispatch_request;
- }
+ if (rq && dd->batching < dd->fifo_batch)
+ /* we have a next request are still entitled to batch */
+ goto dispatch_request;
/*
* at this point we are not running a batch. select the appropriate
--
1.5.4.5
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH 2/3] deadline-iosched: non-functional fixes
2008-08-14 8:17 [PATCH 0/3] deadline-iosched: performance, style and documentation changes Aaron Carroll
2008-08-14 8:17 ` [PATCH 1/3] deadline-iosched: allow non-sequential batching Aaron Carroll
@ 2008-08-14 8:17 ` Aaron Carroll
2008-08-14 8:17 ` [PATCH 3/3] block: update documentation for deadline fifo_batch tunable Aaron Carroll
2008-08-14 9:41 ` [PATCH 0/3] deadline-iosched: performance, style and documentation changes Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Aaron Carroll @ 2008-08-14 8:17 UTC (permalink / raw)
To: jens.axboe; +Cc: linux-kernel
* convert goto to simpler while loop;
* use rq_end_sector() instead of computing manually;
* fix false comments;
* remove spurious whitespace;
* convert rq_rb_root macro to an inline function.
Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
---
block/deadline-iosched.c | 26 +++++++++++++-------------
1 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 07b80e4..fd31117 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -33,7 +33,7 @@ struct deadline_data {
*/
struct rb_root sort_list[2];
struct list_head fifo_list[2];
-
+
/*
* next in sort order. read, write or both are NULL
*/
@@ -53,7 +53,11 @@ struct deadline_data {
static void deadline_move_request(struct deadline_data *, struct request *);
-#define RQ_RB_ROOT(dd, rq) (&(dd)->sort_list[rq_data_dir((rq))])
+static inline struct rb_root *
+deadline_rb_root(struct deadline_data *dd, struct request *rq)
+{
+ return &dd->sort_list[rq_data_dir(rq)];
+}
/*
* get the request after `rq' in sector-sorted order
@@ -72,15 +76,11 @@ deadline_latter_request(struct request *rq)
static void
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
{
- struct rb_root *root = RQ_RB_ROOT(dd, rq);
+ struct rb_root *root = deadline_rb_root(dd, rq);
struct request *__alias;
-retry:
- __alias = elv_rb_add(root, rq);
- if (unlikely(__alias)) {
+ while (unlikely(__alias = elv_rb_add(root, rq)))
deadline_move_request(dd, __alias);
- goto retry;
- }
}
static inline void
@@ -91,7 +91,7 @@ deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
if (dd->next_rq[data_dir] == rq)
dd->next_rq[data_dir] = deadline_latter_request(rq);
- elv_rb_del(RQ_RB_ROOT(dd, rq), rq);
+ elv_rb_del(deadline_rb_root(dd, rq), rq);
}
/*
@@ -106,7 +106,7 @@ deadline_add_request(struct request_queue *q, struct request *rq)
deadline_add_rq_rb(dd, rq);
/*
- * set expire time (only used for reads) and add to fifo list
+ * set expire time and add to fifo list
*/
rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
@@ -162,7 +162,7 @@ static void deadline_merged_request(struct request_queue *q,
* if the merge was a front merge, we need to reposition request
*/
if (type == ELEVATOR_FRONT_MERGE) {
- elv_rb_del(RQ_RB_ROOT(dd, req), req);
+ elv_rb_del(deadline_rb_root(dd, req), req);
deadline_add_rq_rb(dd, req);
}
}
@@ -212,7 +212,7 @@ deadline_move_request(struct deadline_data *dd, struct request *rq)
dd->next_rq[WRITE] = NULL;
dd->next_rq[data_dir] = deadline_latter_request(rq);
- dd->last_sector = rq->sector + rq->nr_sectors;
+ dd->last_sector = rq_end_sector(rq);
/*
* take it off the sort and fifo list, move
@@ -222,7 +222,7 @@ deadline_move_request(struct deadline_data *dd, struct request *rq)
}
/*
- * deadline_check_fifo returns 0 if there are no expired reads on the fifo,
+ * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
* 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
*/
static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
--
1.5.4.5
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH 3/3] block: update documentation for deadline fifo_batch tunable
2008-08-14 8:17 [PATCH 0/3] deadline-iosched: performance, style and documentation changes Aaron Carroll
2008-08-14 8:17 ` [PATCH 1/3] deadline-iosched: allow non-sequential batching Aaron Carroll
2008-08-14 8:17 ` [PATCH 2/3] deadline-iosched: non-functional fixes Aaron Carroll
@ 2008-08-14 8:17 ` Aaron Carroll
2008-08-14 9:41 ` [PATCH 0/3] deadline-iosched: performance, style and documentation changes Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Aaron Carroll @ 2008-08-14 8:17 UTC (permalink / raw)
To: jens.axboe; +Cc: linux-kernel
Update the description of fifo_batch to match the current implementation,
and include a description of how to tune it.
Signed-off-by: Aaron Carroll <aaronc@gelato.unsw.edu.au>
---
Documentation/block/deadline-iosched.txt | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/Documentation/block/deadline-iosched.txt b/Documentation/block/deadline-iosched.txt
index c23cab1..7257676 100644
--- a/Documentation/block/deadline-iosched.txt
+++ b/Documentation/block/deadline-iosched.txt
@@ -30,12 +30,18 @@ write_expire (in ms)
Similar to read_expire mentioned above, but for writes.
-fifo_batch
+fifo_batch (number of requests)
----------
-When a read request expires its deadline, we must move some requests from
-the sorted io scheduler list to the block device dispatch queue. fifo_batch
-controls how many requests we move.
+Requests are grouped into ``batches'' of a particular data direction (read or
+write) which are serviced in increasing sector order. To limit extra seeking,
+deadline expiries are only checked between batches. fifo_batch controls the
+maximum number of requests per batch.
+
+This parameter tunes the balance between per-request latency and aggregate
+throughput. When low latency is the primary concern, smaller is better (where
+a value of 1 yields first-come first-served behaviour). Increasing fifo_batch
+generally improves throughput, at the cost of latency variation.
writes_starved (number of dispatches)
--
1.5.4.5
^ permalink raw reply related [flat|nested] 5+ messages in thread