linux-kernel - Re: [PATCH 0/2] null

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Date:   Tue, 10 Jul 2018 18:49:17 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "mb@...htnvm.io" <mb@...htnvm.io>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "loberman@...hat.com" <loberman@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Damien Le Moal <Damien.LeMoal@....com>
Subject: Re: [PATCH 0/2] null_blk: zone support

On Tue, 2018-07-10 at 12:45 -0600, Jens Axboe wrote:
> The difference between the job file and the
> workload run can be huge. Consider something really basic:
> 
> [randwrites]
> bs=4k
> rw=randwrite
> 
> which would be 100% random 4k writes. If I run this on a zoned device,
> then that'd turn into 100% sequential writes.

That's not correct. The ZBD code in the github pull request serializes writes
per zone, not globally.

> > What I derived from the fio source code is as follows (please correct me
> > if I got anything wrong):
> > * The purpose of the zonesize, zonerange and zoneskip job options is to
> >   limit the I/O range to a single zone with size "zonesize". The I/O
> >   pattern for zoned block devices is different: I/O happens in multiple
> >   zones simultaneously. The number of zones to which I/O happens is
> >   called the number of open zones.
> 
> The only difference is that fio currently only has one zone active. When
> it finishes one, it goes to the next. See my above suggestion on adding
> the notion of open zones, which would extend this to more than 1.

Thanks, I will look into this.

Bart.