Re: disk statistics issue in 2.6.27

[Miquel van Smoorenburg <mikevs@xs4all.net>]

On Wed, 2008-10-22 at 19:17 +0200, Jens Axboe wrote:
> On Wed, Oct 22 2008, Miquel van Smoorenburg wrote:
> > On Mon, 2008-10-20 at 19:12 +0200, Jens Axboe wrote:
> > > On Sun, Oct 19 2008, Miquel van Smoorenburg wrote:
>
> > > > I noticed that the "iostat -k -x 2" output does't make any sense.
> > > > The number of reads/sec and number of writes/sec are about what I
> > > > would expect, and so are the other fields, but rkB/sec and wkB/sec
> > > > are  completely off-scale: gigabytes read/written per second.
> > >
> > 
> > > Are the reported values in iostat any sort of multiple of the real
> > > throughtput, or is is just insanely large?
> > 
> > It looks like it's a multiple, but it appears to vary between 128 and
> > 512, and is different for reads and writes, so I do not know what to
> > make of it.
> > 

I added some debug statements to block/blk-core.c, and it appears that
blk_end_io() is always called with nr_bytes == 16320 Kbytes (16711680).

Ofcourse I should have noticed earlier that iostat -x 2 always prints
32640 as "average request size" (in sectors).

Mike.