On Sun, Feb 04 2001, LA Walsh wrote:
> Seems to have gotten a bit worse. Vmstat output after 'vmware' had completed
> write -- but system unresponsive and writing out a 155M file...
Your numbers seem way too much off to have much to do with i/o scheduling
fairness, but there is a slight bug due to the merge and insertion scan
being done at once now. So you could try with attached patch and see
if it makes any difference whatsoever.
> Those columns are output from a 'vmstat 5'. Meaning it took about 70 seconds
> to write out 158M. Or about 2.2M/s. That's probably not bad. It still locks
> up the system for over a minute though -- which is really undesirable performance
> for interactive use. I'm guessing the vmstat output numbers are showing 4K? 8K?
> blocks? 8K would about make sense for the 2.2M average.
Most likely 4kB blocks. I'd say the numbers are pretty bad...
--
Jens Axboe
--- /opt/kernel/linux-2.4.2-pre1/drivers/block/elevator.c Tue Jan 30 13:32:10
2001
+++ drivers/block/elevator.c Mon Feb 5 01:26:49 2001
@@ -35,6 +35,7 @@
struct list_head *entry = &q->queue_head;
unsigned int count = bh->b_size >> 9, ret = ELEVATOR_NO_MERGE;
+ *req = NULL;
while ((entry = entry->prev) != head) {
struct request *__rq = blkdev_entry_to_request(entry);
@@ -46,10 +47,13 @@
break;
}
+
if (__rq->sem)
continue;
if (__rq->cmd != rw)
continue;
+ if (!*req && BHRQ_IN_ORDER(bh, __rq))
+ *req = __rq;
if (__rq->rq_dev != bh->b_rdev)
continue;
if (__rq->nr_sectors + count > max_sectors)
@@ -65,8 +69,7 @@
__rq->elevator_sequence -= count;
*req = __rq;
break;
- } else if (!*req && BHRQ_IN_ORDER(bh, __rq))
- *req = __rq;
+ }
}
return ret;
--- /opt/kernel/linux-2.4.2-pre1/drivers/block/ll_rw_blk.c Tue Jan 30 13:32:10
2001
+++ drivers/block/ll_rw_blk.c Mon Feb 5 02:02:22 2001
@@ -628,11 +628,19 @@
&& atomic_read(&queued_sectors) < low_queued_sectors)
wake_up(&blk_buffers_wait);
+ if (!list_empty(&q->request_freelist[rw])) {
+ blk_refill_freelist(q, rw);
+ list_add(&req->table, &q->request_freelist[rw]);
+ if (waitqueue_active(&q->wait_for_request))
+ wake_up_nr(&q->wait_for_request, 2);
+ return;
+ }
+
/*
- * Add to pending free list and batch wakeups
+ * free list is empty, add to pending free list and
+ * batch wakeups
*/
list_add(&req->table, &q->pending_freelist[rw]);
-
if (++q->pending_free[rw] >= batch_requests) {
int wake_up = q->pending_free[rw];
blk_refill_freelist(q, rw);
@@ -705,7 +713,7 @@
{
unsigned int sector, count;
int max_segments = MAX_SEGMENTS;
- struct request * req = NULL, *freereq = NULL;
+ struct request *req, *freereq = NULL;
int rw_ahead, max_sectors, el_ret;
struct list_head *head, *insert_here;
int latency;
@@ -767,6 +775,10 @@
el_ret = elevator->elevator_merge_fn(q, &req, head, bh, rw,
max_sectors, max_segments);
+ if (el_ret && q->head_active && !q->plugged
+ && req->queue.prev == &q->queue_head)
+ BUG();
+
switch (el_ret) {
case ELEVATOR_BACK_MERGE:
