Messages in this thread Patch in this message | | | From | "Chen, Kenneth W" <> | Subject | RE: [patch] use cheaper elv_queue_empty when unplug a device | Date | Tue, 29 Mar 2005 11:02:13 -0800 |
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Nick Piggin wrote on Tuesday, March 29, 2005 1:20 AM > Speaking of which, I've had a few ideas lying around for possible > performance improvement in the block code. > > I haven't used a big disk array (or tried any simulation), but I'll > attach the patch if you're looking into that area. > > linux-2.6-npiggin/drivers/block/ll_rw_blk.c | 63 ++++++++++------------------ > 1 files changed, 23 insertions(+), 40 deletions(-) > > diff -puN drivers/block/ll_rw_blk.c~blk-efficient drivers/block/ll_rw_blk.c > --- linux-2.6/drivers/block/ll_rw_blk.c~blk-efficient 2005-03-29 19:00:07.000000000 +1000 > +++ linux-2.6-npiggin/drivers/block/ll_rw_blk.c 2005-03-29 19:10:45.000000000 +1000 > @@ -2557,7 +2557,7 @@ EXPORT_SYMBOL(__blk_attempt_remerge); > > static int __make_request(request_queue_t *q, struct bio *bio) > { > - struct request *req, *freereq = NULL; > + struct request *req; > int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err; > sector_t sector; > > @@ -2577,19 +2577,18 @@ static int __make_request(request_queue_ > > -again: > spin_lock_irq(q->queue_lock); > > if (elv_queue_empty(q)) { >
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> +get_rq: > /* > - * Grab a free request from the freelist - if that is empty, check > - * if we are doing read ahead and abort instead of blocking for > - * a free slot. > + * Grab a free request. This is might sleep but can not fail. > + */ > + spin_unlock_irq(q->queue_lock); > + req = get_request_wait(q, rw); > + /* > + * After dropping the lock and possibly sleeping here, our request > + * may now be mergeable after it had proven unmergeable (above). > + * We don't worry about that case for efficiency. It won't happen > + * often, and the elevators are able to handle it. > */ > -get_rq: > - if (freereq) { > - req = freereq; > - freereq = NULL; > - } else { > - spin_unlock_irq(q->queue_lock); > - if ((freereq = get_request(q, rw, GFP_ATOMIC)) == NULL) { > - /* > - * READA bit set > - */ > - err = -EWOULDBLOCK; > - if (bio_rw_ahead(bio)) > - goto end_io; > - > - freereq = get_request_wait(q, rw); > - } > - goto again; > - } > > req->flags |= REQ_CMD; >
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> @@ -2693,10 +2675,11 @@ get_rq: > req->rq_disk = bio->bi_bdev->bd_disk; > req->start_time = jiffies; > > + spin_lock_irq(q->queue_lock); > + if (elv_queue_empty(q)) > + blk_plug_device(q); > add_request(q, req); > out: > - if (freereq) > - __blk_put_request(q, freereq); > if (bio_sync(bio)) > __generic_unplug_device(q);
This part of change in __make_request() is very welcome for enterprise workload. I have an unpublished version of patch does something similar. I will look through all other changes in your patch.
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