Re: extra I/O at the start of disk zone test?

On Thu, Jan 31 2008, Ryan Thomas wrote:
> Yes, that aligns the zones for me.

Great, I've committed the fix. Thanks for reporting it!

>
> Thanks
> Ryan
>
>
> -----Original Message-----
> From: Jens Axboe [mailto:jens.axboe_at_oracle.com]
> Sent: Thursday, January 31, 2008 7:25 AM
> To: Ryan Thomas
> Cc: fio-devel_at_kernel.dk
> Subject: Re: extra I/O at the start of disk zone test?
>
> On Thu, Jan 31 2008, Ryan Thomas wrote:
> > With the following job description
> >
> >
> > [global]
> > bs=1k
> > direct=1
> > rw=read
> > ioengine=libaio
> > iodepth=2
> > zonesize=1k
> > zoneskip=1023k
> > write_bw_log
> >
> > [/dev/cciss/c0d1]
> > write_iolog=foo2
> >
> > The idea here is that I wanted to line up my zones to start at 1M
> > boundaries across the disk by writing 1k and skipping the next 1023k.
> > In practice I don't get the alignment because of an extra initial I/O.
> > I get an iolog that looks like
> >
> >
> >
> > # head foo2
> >
> > fio version 2 iolog
> >
> > /dev/cciss/c0d1 add
> >
> > /dev/cciss/c0d1 open
> >
> > /dev/cciss/c0d1 read 0 1024
> >
> > /dev/cciss/c0d1 read 1024 1024
> >
> > /dev/cciss/c0d1 read 1049600 1024
> >
> > /dev/cciss/c0d1 read 2098176 1024
> >
> >
> >
> > There's a read that I don't expect in that log, namely the read
> starting
> > at byte 1024. Because that read is there, the disk zones get offset
> by
> > one block. I expected output like
>
> It's due to how fio accounts the zone bytes. Right now it does them when
> the io completes, but that's clearly not correct for iodepth > 1. The
> patch below should fix things up for you, can you confirm it works?
>
> diff --git a/io_u.c b/io_u.c
> index 7890a87..8201ccd 100644
> --- a/io_u.c
> +++ b/io_u.c
> @@ -375,6 +375,7 @@ static int fill_io_u(struct thread_data *td, struct
> io_u *io_u)
> * If using a write iolog, store this entry.
> */
> out:
> + td->zone_bytes += io_u->buflen;
> log_io_u(td, io_u);
> return 0;
> }
> @@ -765,7 +766,6 @@ static void io_completed(struct thread_data *td,
> struct io_u *io_u,
>
> td->io_blocks[idx]++;
> td->io_bytes[idx] += bytes;
> - td->zone_bytes += bytes;
> td->this_io_bytes[idx] += bytes;
>
> io_u->file->last_completed_pos = io_u->endpos;
>
> --
> Jens Axboe
>

-- 
Jens Axboe