Re: 2.6.0-test8/test9 io scheduler needs tuning?

[Nick Piggin]

cliff white wrote:

> On Tue, 28 Oct 2003 05:52:45 +0800
> Michael Frank <mhf@xxxxxxxxxxxxx> wrote:
>
>
> > To my surprise 2.6 - which used to do better then 2.4 - does no longer 
> > handle these test that well.
> >
> > Generally, IDE IO throughput is _very_ uneven and IO _stops_ at times with the
> > system cpu load very high (and the disk LED off).
> >
> > IMHO the CPU scheduling is OK but the IO scheduling acts up here.
> >
> > The test system is a 2.4GHz P4 with 512M RAM and a 55MB/s udma IDE harddisk.
> >
> > The tests load the system to loadavg > 30. IO should be about 20MB/s on avg.
> >
> > Enclosed are vmstat -1 logs for 2.6-test9-Vanilla, followed by 2.6-test8-Vanilla 
> > (-mm1 behaves similar), 2.4.22-Vanilla and 2.4.21+swsusp all compiled wo preempt.
> >
> > IO on 2.6 stops now for seconds at a time. -test8 is worse than -test9
>
> We see the same delta at OSDL. Try repeating your tests with 'elevator=deadline' 
> to confirm.
> For example, on the 8-cpu platform:
> STP id Kernel Name         MaxJPM      Change  Options
> 281669 linux-2.6.0-test8   7014.42      0.0    
> 281671 linux-2.6.0-test8   8294.94     +18.26%  elevator=deadline
>
> The -mm kernels don't show this big delta. We also do not see this delta on
> smaller machines

I'm working with Randy to fix this. Attached is what I have so far. See how
you go with it.

 linux-2.6-npiggin/drivers/block/as-iosched.c |   30 ++++++---------------------
 1 files changed, 7 insertions(+), 23 deletions(-)

diff -puN drivers/block/as-iosched.c~as-fix drivers/block/as-iosched.c
--- linux-2.6/drivers/block/as-iosched.c~as-fix	2003-10-27 14:53:47.000000000 +1100
+++ linux-2.6-npiggin/drivers/block/as-iosched.c	2003-10-27 14:54:04.000000000 +1100
@@ -99,7 +99,6 @@ struct as_data {
 	sector_t last_sector[2];	/* last REQ_SYNC & REQ_ASYNC sectors */
 	struct list_head *dispatch;	/* driver dispatch queue */
 	struct list_head *hash;		/* request hash */
-	unsigned long new_success; /* anticipation success on new proc */
 	unsigned long current_batch_expires;
 	unsigned long last_check_fifo[2];
 	int changed_batch;		/* 1: waiting for old batch to end */
@@ -585,18 +584,11 @@ static void as_antic_stop(struct as_data
 	int status = ad->antic_status;
 
 	if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
-		struct as_io_context *aic;
-
 		if (status == ANTIC_WAIT_NEXT)
 			del_timer(&ad->antic_timer);
 		ad->antic_status = ANTIC_FINISHED;
 		/* see as_work_handler */
 		kblockd_schedule_work(&ad->antic_work);
-
-		aic = ad->io_context->aic;
-		if (aic->seek_samples == 0)
-			/* new process */
-			ad->new_success = (ad->new_success * 3) / 4 + 256;
 	}
 }
 
@@ -612,14 +604,8 @@ static void as_antic_timeout(unsigned lo
 	spin_lock_irqsave(q->queue_lock, flags);
 	if (ad->antic_status == ANTIC_WAIT_REQ
 			|| ad->antic_status == ANTIC_WAIT_NEXT) {
-		struct as_io_context *aic;
 		ad->antic_status = ANTIC_FINISHED;
 		kblockd_schedule_work(&ad->antic_work);
-
-		aic = ad->io_context->aic;
-		if (aic->seek_samples == 0)
-			/* new process */
-			ad->new_success = (ad->new_success * 3) / 4;
 	}
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
@@ -708,11 +694,10 @@ static int as_can_break_anticipation(str
 		return 1;
 	}
 
-	if (ad->new_success < 256 &&
-			(aic->seek_samples == 0 || aic->ttime_samples == 0)) {
+	if (aic->seek_samples == 0 || aic->ttime_samples == 0) {
 		/*
-		 * Process has just started IO and we have a bad history of
-		 * success anticipating on new processes!
+		 * Process has just started IO. Don't anticipate.
+		 * TODO! Must fix this up.
 		 */
 		return 1;
 	}
@@ -1292,7 +1277,7 @@ fifo_expired:
 
 		ad->changed_batch = 0;
 
-		arq->request->flags |= REQ_SOFTBARRIER;
+//		arq->request->flags |= REQ_SOFTBARRIER;
 	}
 
 	/*
@@ -1391,6 +1376,7 @@ static void as_add_request(struct as_dat
 
 	} else {
 		as_add_aliased_request(ad, arq, alias);
+
 		/*
 		 * have we been anticipating this request?
 		 * or does it come from the same process as the one we are
@@ -1427,8 +1413,6 @@ static void as_requeue_request(request_q
 
 	/* Stop anticipating - let this request get through */
 	as_antic_stop(ad);
-
-	return;
 }
 
 static void
@@ -1437,10 +1421,12 @@ as_insert_request(request_queue_t *q, st
 	struct as_data *ad = q->elevator.elevator_data;
 	struct as_rq *arq = RQ_DATA(rq);
 
+#if 0
 	/* barriers must flush the reorder queue */
 	if (unlikely(rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)
 			&& where == ELEVATOR_INSERT_SORT))
 		where = ELEVATOR_INSERT_BACK;
+#endif
 
 	switch (where) {
 		case ELEVATOR_INSERT_BACK:
@@ -1823,8 +1809,6 @@ static int as_init(request_queue_t *q, e
 	if (ad->write_batch_count < 2)
 		ad->write_batch_count = 2;
 
-	ad->new_success = 512;
-
 	return 0;
 }
 

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