From: Nick Piggin <piggin@cyberone.com.au>
The problem was last_request_pos being reset to the new request before
being used to calculate the seek delta. Stupid mistake - I have seen it
before, but I guess either I forgot to fix it or it crept back in. Also a
few small tweaks to improve seeky loads.
Anyway, previously the regressed rawread workload would get ~600K/s with
antic_expire = 10, ~900K/s with antic_expire = 0. Now there isn't a big
difference either way at ~900K/s (I didn't bother doing a full run, just
looked at vmstat output because its consistent).
drivers/block/as-iosched.c | 15 +++++++--------
1 files changed, 7 insertions(+), 8 deletions(-)
diff -puN drivers/block/as-iosched.c~as-fix-seeky-loads drivers/block/as-iosched.c
--- 25/drivers/block/as-iosched.c~as-fix-seeky-loads 2003-06-11 18:47:19.000000000 -0700
+++ 25-akpm/drivers/block/as-iosched.c 2003-06-11 18:47:19.000000000 -0700
@@ -721,13 +721,13 @@ static int as_close_req(struct as_data *
delay = ((jiffies - ad->antic_start) * 1000) / HZ;
if (delay <= 1)
- delta = 32;
+ delta = 64;
else if (delay <= 20 && delay <= ad->antic_expire)
- delta = 32 << (delay-1);
+ delta = 64 << (delay-1);
else
return 1;
- return (last - delta <= next) && (next <= last + delta);
+ return (last - (delta>>1) <= next) && (next <= last + delta);
}
/*
@@ -794,7 +794,8 @@ static int as_can_break_anticipation(str
s = arq->request->sector - ad->last_sector[REQ_SYNC];
else
s = ad->last_sector[REQ_SYNC] - arq->request->sector;
- if (aic->seek_mean > s) {
+
+ if (aic->seek_mean > (s>>1)) {
/* this request is better than what we're expecting */
return 1;
}
@@ -877,8 +878,6 @@ static void as_update_iohist(struct as_i
}
/* Calculate read -> read seek distance */
- aic->last_request_pos = rq->sector + rq->nr_sectors;
-
if (!aic->seek_samples)
seek_dist = 0;
else if (aic->last_request_pos < rq->sector)
@@ -886,7 +885,8 @@ static void as_update_iohist(struct as_i
else
seek_dist = aic->last_request_pos - rq->sector;
-#if 0 /* TODO does this fix IBM's rawio random reads? */
+ aic->last_request_pos = rq->sector + rq->nr_sectors;
+
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
@@ -897,7 +897,6 @@ static void as_update_iohist(struct as_i
else
seek_dist = min(seek_dist, (aic->seek_mean * 4)
+ 2*1024*64);
-#endif
aic->seek_samples += 256;
aic->seek_total += 256*seek_dist;
_