Patch from Nick Piggin <piggin@cyberone.com.au>
This is pretty well correct I think. If we get a write from the
process we are anticipating a read from, then the read isn't sync,
right?
I still don't think this will help the Oracle load, however.
drivers/block/as-iosched.c | 68 ++++++++++++++++++++++++---------------------
1 files changed, 37 insertions(+), 31 deletions(-)
diff -puN drivers/block/as-iosched.c~as-break-anticipation-on-write drivers/block/as-iosched.c
--- 25/drivers/block/as-iosched.c~as-break-anticipation-on-write Mon Feb 24 15:09:23 2003
+++ 25-akpm/drivers/block/as-iosched.c Mon Feb 24 15:09:23 2003
@@ -33,6 +33,7 @@ struct ant_stats {
int expired_fifo_writes;
int close_requests;
int matching_ids;
+ int broken_by_write;
int ant_delay_hist[100]; /* milliseconds */
@@ -749,17 +750,23 @@ elevator_wrap:
}
/*
- * as_antic_req, has @ad been anticipating this @arq?
+ * as_antic_req returns true if we have been anticipating this request.
+ *
+ * It also returns true if the process against which we are anticipating
+ * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
+ * dispatch it ASAP, because we know that application will not be submitting
+ * any new reads.
*/
-static int
-as_antic_req(struct as_data *ad, struct as_rq *arq)
+static int as_antic_req(struct as_data *ad, struct as_rq *arq)
{
- if (as_close_req(ad, arq)) {
+ if (rq_data_dir(arq->request) == READ && as_close_req(ad, arq)) {
ant_stats.close_requests++;
return 1;
}
if (ad->current_id == arq->request_id) {
ant_stats.matching_ids++;
+ if (rq_data_dir(arq->request) == WRITE)
+ ant_stats.broken_by_write++;
return 1;
}
return 0;
@@ -770,12 +777,10 @@ as_antic_req(struct as_data *ad, struct
* the sort_list. This function keeps caches up to date, and checks if the
* request might be one we are "anticipating"
*/
-static void
-as_update_arq(struct as_data *ad, struct as_rq *arq)
+static void as_update_arq(struct as_data *ad, struct as_rq *arq)
{
const int data_dir = rq_data_dir(arq->request);
-
if (data_dir == READ)
ant_stats.reads++;
else
@@ -784,11 +789,12 @@ as_update_arq(struct as_data *ad, struct
/* keep the next_arq cache up to date */
ad->next_arq[data_dir] = as_choose_req(ad, arq, ad->next_arq[data_dir]);
- /* have we been anticipating this request? */
- if (ad->antic_status != ANTIC_OFF && data_dir == READ
- && as_antic_req(ad, arq)) {
-
- /* statistics stuff */
+ /*
+ * have we been anticipating this request?
+ * or does it come from the same process as the one we are anticipating
+ * for?
+ */
+ if (ad->antic_status != ANTIC_OFF && as_antic_req(ad, arq)) {
sector_t last = ad->last_sector[data_dir];
sector_t this = arq->request->sector;
unsigned long delay = jiffies - ad->antic_start;
@@ -796,24 +802,25 @@ as_update_arq(struct as_data *ad, struct
int neg;
int log2;
- if (delay >= ARRAY_SIZE(ant_stats.ant_delay_hist))
- delay = ARRAY_SIZE(ant_stats.ant_delay_hist) - 1;
- ant_stats.ant_delay_hist[delay]++;
- ant_stats.anticipate_hits++;
-
- lba_offset = this - last;
- neg = 0;
- if (lba_offset < 0) {
- lba_offset = -lba_offset;
- neg = 1;
+ if (data_dir == READ) {
+ if (delay >= ARRAY_SIZE(ant_stats.ant_delay_hist))
+ delay = ARRAY_SIZE(ant_stats.ant_delay_hist)-1;
+ ant_stats.ant_delay_hist[delay]++;
+ ant_stats.anticipate_hits++;
+
+ lba_offset = this - last;
+ neg = 0;
+ if (lba_offset < 0) {
+ lba_offset = -lba_offset;
+ neg = 1;
+ }
+ log2 = ffs(lba_offset);
+ BUG_ON(log2 >= 32);
+ if (neg)
+ ant_stats.lba_backward_offsets[log2]++;
+ else
+ ant_stats.lba_forward_offsets[log2]++;
}
- log2 = ffs(lba_offset);
- BUG_ON(log2 >= 32);
- if (neg)
- ant_stats.lba_backward_offsets[log2]++;
- else
- ant_stats.lba_forward_offsets[log2]++;
-
del_timer(&ad->antic_timer);
ad->antic_status = ANTIC_FINISHED;
if (arq)
@@ -826,8 +833,7 @@ as_update_arq(struct as_data *ad, struct
* can_start_anticipation indicates weather we should either run arq
* or keep anticipating a better request.
*/
-static int
-can_start_anticipation(struct as_data *ad, struct as_rq *arq)
+static int can_start_anticipation(struct as_data *ad, struct as_rq *arq)
{
if (ad->antic_status == ANTIC_FINISHED)
/*
_