[Devel] Re: IO scheduler based IO controller V10

[Mike Galbraith]

On Sun, 2009-09-27 at 20:16 +0200, Mike Galbraith wrote:
> On Sun, 2009-09-27 at 18:42 +0200, Jens Axboe wrote:

> I'll give it a shot first thing in the A.M.

> > diff --git a/block/elevator.c b/block/elevator.c
> > index 1975b61..d00a72b 100644
> > --- a/block/elevator.c
> > +++ b/block/elevator.c
> > @@ -497,9 +497,17 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
> >  	 * See if our hash lookup can find a potential backmerge.
> >  	 */
> >  	__rq = elv_rqhash_find(q, bio->bi_sector);
> > -	if (__rq && elv_rq_merge_ok(__rq, bio)) {
> > -		*req = __rq;
> > -		return ELEVATOR_BACK_MERGE;
> > +	if (__rq) {
> > +		/*
> > +		 * If requests are queued behind this one, disallow merge. This
> > +		 * prevents streaming IO from continually passing new IO.
> > +		 */
> > +		if (elv_latter_request(q, __rq))
> > +			return ELEVATOR_NO_MERGE;
> > +		if (elv_rq_merge_ok(__rq, bio)) {
> > +			*req = __rq;
> > +			return ELEVATOR_BACK_MERGE;
> > +		}
> >  	}
> >  
> >  	if (e->ops->elevator_merge_fn)

- = virgin tip v2.6.31-10215-ga3c9602
+ = with patchlet
                                                            Avg
dd pre         67.4     70.9     65.4     68.9     66.2     67.7-
               65.9     68.5     69.8     65.2     65.8     67.0-     Avg
               70.4     70.3     65.1     66.4     70.1     68.4-     67.7-
               73.1     64.6     65.3     65.3     64.9     66.6+     65.6+     .968
               63.8     67.9     65.2     65.1     64.4     65.2+
               64.9     66.3     64.1     65.2     64.8     65.0+
perf stat      8.66    16.29     9.65    14.88     9.45     11.7-
              15.36     9.71    15.47    10.44    12.93     12.7-
              10.55    15.11    10.22    15.35    10.32     12.3-     12.2-
               9.87     7.53    10.62     7.51     9.95      9.0+      9.1+     .745
               7.73    10.12     8.19    11.87     8.07      9.1+
              11.04     7.62    10.14     8.13    10.23      9.4+
dd post        63.4     60.5     66.7     64.5     67.3     64.4-
               64.4     66.8     64.3     61.5     62.0     63.8-
               63.8     64.9     66.2     65.6     66.9     65.4-     64.5-
               60.9     63.4     60.2     63.4     65.5     62.6+     61.8+     .958
               63.3     59.9     61.9     62.7     61.2     61.8+
               60.1     63.7     59.5     61.5     60.6     61.0+


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