From: Nick Piggin <piggin@cyberone.com.au>
This patch makes some minor tweaks to the scheduler. Well
tested. Makes a bit of difference. Especially lower write_expire,
which seems to be good for gcc in contest loads.
Lowered antic_expire a bit. This should help all regressions.
It _may_ be a little too low for old computers whose processes
have high thinktimes and disks have high seek times. We really
want the driver to be able to pass up a guesstimate of the
average seek time of its device. Anyway.
Nick
Here are some results. I'll do some for deadline in a sec.
Cat kernel tree during seq read
mm 15.07
np 14.50
Cat kernel tree during seq write
mm 19.13
np 16.33
ls -l kernel tree during seq read
mm 9.10
np 9.39
ls -l kernel tree during seq write
mm 5.45
np 5.49
Contest - bottom figure is +np
no_load:
Kernel [runs] Time CPU% Loads LCPU% Ratio
2.5.65-mm4 1 68 97.1 0.0 0.0 1.00
2.5.65-mm4 1 69 95.7 0.0 0.0 1.00
io_load:
Kernel [runs] Time CPU% Loads LCPU% Ratio
2.5.65-mm4 1 108 63.9 89.8 23.1 1.59
2.5.65-mm4 1 100 70.0 81.2 22.0 1.45
read_load:
Kernel [runs] Time CPU% Loads LCPU% Ratio
2.5.65-mm4 1 106 67.0 15.9 7.5 1.56
2.5.65-mm4 1 100 72.0 15.6 8.0 1.45
list_load:
Kernel [runs] Time CPU% Loads LCPU% Ratio
2.5.65-mm4 1 97 70.1 7.0 20.6 1.43
2.5.65-mm4 1 94 72.3 6.0 19.1 1.36
tiobench was nothing special. even with large numbers of seq
writers, the lower write_expire hasn't made a noticable impact.
OraSim (np should average slightly better)
mm - 138, 136
np - 129, 140
nickbench - mm
Bench 2 - 2 threads, streaming reader & writer
IO Rate: 40.63 MB/s
Reads per write: 1.80
Bench 3 - 2 threads, streaming readers
IO Rate: 47.08 MB/s
Reads per read: 1.15
Bench 4 - 2 threads, streaming writers
IO Rate: 39.98 MB/s
Writes per write: 1.82
Bench 5 - 1 thread, read then write each block of 1 file
Read then write: 22.64 MB/s
CPU time per byte: 5130.859375 us/B
Bench 6 - 4 threads, streaming readers
IO Rate: 45.01 MB/s
Greatest reads per read unfairness between 4 readers: 0.97
nickbench - np
Bench 2 - 2 threads, streaming reader & writer
IO Rate: 42.19 MB/s
Reads per write: 2.08
Bench 3 - 2 threads, streaming readers
IO Rate: 45.56 MB/s
Reads per read: 1.00
Bench 4 - 2 threads, streaming writers
IO Rate: 40.64 MB/s
Writes per write: 1.68
Bench 5 - 2 thread, read then write each block of 1 file
Read then write: 22.65 MB/s
CPU time per byte: 5238.281250 us/B
Bench 6 - 4 threads, streaming readers
IO Rate: 44.89 MB/s
Greatest reads per read unfairness between 4 readers: 0.95
drivers/block/as-iosched.c | 19 +++++++++----------
1 files changed, 9 insertions(+), 10 deletions(-)
diff -puN drivers/block/as-iosched.c~as-minor-tweaks drivers/block/as-iosched.c
--- 25/drivers/block/as-iosched.c~as-minor-tweaks 2003-03-24 21:28:31.000000000 -0800
+++ 25-akpm/drivers/block/as-iosched.c 2003-03-24 21:28:31.000000000 -0800
@@ -64,7 +64,7 @@ static unsigned long read_expire = HZ /
* ditto for writes, these limits are not hard, even
* if the disk is capable of satisfying them.
*/
-static unsigned long write_expire = HZ / 2;
+static unsigned long write_expire = HZ / 5;
/*
* read_batch_expire describes how long we will allow a stream of reads to
@@ -79,9 +79,9 @@ static unsigned long read_batch_expire =
static unsigned long write_batch_expire = HZ / 20;
/*
- * max time we may wait to anticipate a read
+ * max time we may wait to anticipate a read (default around 6ms)
*/
-static unsigned long antic_expire = HZ / 100;
+static unsigned long antic_expire = ((HZ / 150) ? HZ / 150 : 1);
/*
* This is the per-process anticipatory I/O scheduler state. It is refcounted
@@ -170,7 +170,7 @@ enum anticipation_states {
ANTIC_WAIT_NEXT, /* Currently anticipating a request vs
last read (which has completed) */
ANTIC_FINISHED, /* Anticipating but have found a candidate
- or timed out */
+ * or timed out */
};
/*
@@ -633,9 +633,8 @@ static void as_antic_waitnext(struct as_
&& ad->antic_status != ANTIC_WAIT_REQ);
timeout = ad->antic_start + ad->antic_expire;
-#if 0 /* TODO unif me. This should be fixed. */
timeout = min(timeout, ad->current_batch_expires);
-#endif
+
mod_timer(&ad->antic_timer, timeout);
ad->antic_status = ANTIC_WAIT_NEXT;
@@ -710,7 +709,7 @@ static int as_close_req(struct as_data *
if (delay <= 1)
delta = 32;
- else if (delay <= 20 && delay <= ad->antic_expire / 2)
+ else if (delay <= 20 && delay <= ad->antic_expire)
delta = 32 << (delay-1);
else
return 1;
@@ -771,7 +770,7 @@ static int as_can_break_anticipation(str
return 1;
}
- if (aic && aic->ttime_mean > max(HZ/200, 1)) {
+ if (aic && aic->ttime_mean > ad->antic_expire) {
ant_stats.big_thinktime++;
return 1;
}
@@ -1147,7 +1146,7 @@ static int as_dispatch_request(struct as
ant_stats.expired_write_batches++;
}
- if (!(reads && writes && as_batch_expired(ad))) {
+ if (!(reads && writes && as_batch_expired(ad)) ) {
/*
* batch is still running or no reads or no writes
*/
@@ -1194,7 +1193,7 @@ static int as_dispatch_request(struct as
}
/*
- * there are either no reads or the last batch was a read
+ * the last batch was a read
*/
if (writes) {
_