linux-kernel - Re: [PATCH 12/12] cciss: fix for iostat

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Message-ID: <20061106210504.GK19471@kernel.dk>
Date:	Mon, 6 Nov 2006 22:05:04 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Mike Miller (OS Dev)" <mikem@...rdog.cca.cpqcorp.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 12/12] cciss: fix for iostat

On Mon, Nov 06 2006, Jens Axboe wrote:
> On Mon, Nov 06 2006, Mike Miller (OS Dev) wrote:
> > Patch 12 of 12
> > 
> > This patch replaces complete_buffers with end_that_request_first to fix
> > programs like iostat. This has been broken for the last few kernel releases.
> > Please consider this for inclusion.
> > 
> > Thanks,
> > mikem
> > 
> > Signed-off-by: Mike Miller <mike.miller@...com>
> > 
> > 
> > ---
> > 
> > 
> > ---
> > 
> >  drivers/block/cciss.c |   20 ++++----------------
> >  1 files changed, 4 insertions(+), 16 deletions(-)
> > 
> > diff -puN drivers/block/cciss.c~cciss_update_diskstats_fix drivers/block/cciss.c
> > --- linux-2.6/drivers/block/cciss.c~cciss_update_diskstats_fix	2006-11-06 13:28:53.000000000 -0600
> > +++ linux-2.6-root/drivers/block/cciss.c	2006-11-06 13:28:53.000000000 -0600
> > @@ -1156,18 +1156,6 @@ static int cciss_ioctl(struct inode *ino
> >  	}
> >  }
> >  
> > -static inline void complete_buffers(struct bio *bio, int status)
> > -{
> > -	while (bio) {
> > -		struct bio *xbh = bio->bi_next;
> > -		int nr_sectors = bio_sectors(bio);
> > -
> > -		bio->bi_next = NULL;
> > -		bio_endio(bio, nr_sectors << 9, status ? 0 : -EIO);
> > -		bio = xbh;
> > -	}
> > -}
> > -
> >  static void cciss_check_queues(ctlr_info_t *h)
> >  {
> >  	int start_queue = h->next_to_run;
> > @@ -1236,15 +1224,15 @@ static void cciss_softirq_done(struct re
> >  		pci_unmap_page(h->pdev, temp64.val, cmd->SG[i].Len, ddir);
> >  	}
> >  
> > -	complete_buffers(rq->bio, rq->errors);
> > -
> >  #ifdef CCISS_DEBUG
> >  	printk("Done with %p\n", rq);
> >  #endif				/* CCISS_DEBUG */
> >  
> > -	add_disk_randomness(rq->rq_disk);
> >  	spin_lock_irqsave(&h->lock, flags);
> > -	end_that_request_last(rq, rq->errors);
> > +	if (!end_that_request_first(rq, rq->errors, rq->nr_sectors)) {
> > +		add_disk_randomness(rq->rq_disk);
> > +		end_that_request_last(rq, rq->errors);
> > +	}
> >  	cmd_free(h, cmd, 1);
> >  	cciss_check_queues(h);
> >  	spin_unlock_irqrestore(&h->lock, flags);
> 
> Ah, so there's where that went. Your code isn't clear, though -
> end_that_request_first() _must_ return 0, so the above looks confusing.
> It would look cleaner and more informative like:
> 
>         if (end_that_request_first(rq, rq->errors, rq->nr_sectors))
>                 BUG();
> 
>         add_disk_randomness(rq->rq_disk);
>         end_that_request_last(rq, rq->errors);
>         ...
> 
> and so on. Additionally you don't need the lock for
> end_that_request_first(), so it's a lot more optimal to rearrange it
> again.
> 
>         add_disk_randomness(rq->rq_disk);
>         if (end_that_request_first(rq, rq->errors, rq->nr_sectors))
>                 BUG();
> 
>         spin_lock_irqsave(&h->lock, flags);
>         end_that_request_last(rq, rq->errors);
>         cmd_free(h, cmd, 1);
>         ...
> 
> Not only cleaner to read since it's obvious what will happen, also moves
> the heavy path (end_that_request_first()) outside of the controller
> lock.

IOW, simple one-liner fix:

diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index 6ffe2b2..f9f128a 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -1299,6 +1299,7 @@ static void cciss_softirq_done(struct re
 	}
 
 	complete_buffers(rq->bio, rq->errors);
+	disk_stat_add(rq->rq_disk, sectors[rq_data_dir(rq)], rq->nr_sectors);
 
 #ifdef CCISS_DEBUG
 	printk("Done with %p\n", rq);

-- 
Jens Axboe

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