Message-ID: <20120924113718.GK20960@dastard>
Date:	Mon, 24 Sep 2012 21:37:18 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, xfs@....sgi.com, hch@....de
Subject: Re: [PATCH 1/6] xfstest: add fio git submodule

On Mon, Sep 24, 2012 at 02:03:42PM +0400, Dmitry Monakhov wrote:
> On Sun, 23 Sep 2012 22:16:57 -0500, Eric Sandeen <sandeen@...hat.com> wrote:
> > On 9/23/12 2:24 PM, Dmitry Monakhov wrote:
> > > FIO is very flexible io generator, i would call it IO swiss knife.
> > > Currently we have tonnes of hardcoded application which reproduces
> > > some predefined scenario. This approach has obvious dissadvantages
> > > 1) Lack of flexability: once written it is hard to modify it in future
> > > 2) Code base is large, many routines written again and again
> > > 
> > > At the same time add new fio based tast is just add simle INI file.
> > > This greatly simplify code review. I do beleve that some day we will
> > > replace most of hardcoded io binaries with fio.
> > 
> > The submodule approach is interesting, but I wonder - we have quite a few
> > dependencies on other binaries already; what are the pros and cons of creating
> > this as a git submodule vs. simply expecting fio to be installed on the
> > system like any of the other dependencies we have today?
> Pro:
>  P1) allow to specify exact commit as a submodule HEAD this guarantee
>      that we will have known version and functionality regardless to
>      distribution package manager (which are known to be very conservative)

You haven't provided a method to do this in this patch. All
you've provided is a submodule that tracks the fio tree head.
All this needs to be properly documented in the README file, at
minimum.

And conservative is good, too. I don't want tests to fail because of
rapid changes in the fio tree causing regressions in fio itself. The
tools that xfstests depends on need to be stable and relatively
unchanging, because we're not testing them - we're testing the
filesystem. The less the environemnt changes around the things we're
actually supposed to be regression testing, the better.

>  P2) Prevent duplicating of source code (fsstress.c/aio-stress.c and
>      etc).  If some one want to add new feature to submodule he
>      simply push it to official submodule repo and move submodule HEAD
>      In that both parties(submodule maintainer and project maintainer)
>      will benefit because new features will be available to every
>      submodule user
> Cons:
>  C1) New dependencies
>  C2) Learn people how to work with submodules
> 
> I'll not assume (C2) as a serious argument because this is just one more
> git's command. For most users should just add new option to clone:
> git clone --recursive git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git

Doesn't work for me. I keep local mirrors of all git trees that I
use regularly and update them by cron jobs so that I don't have to
go to the internet for every local tree that I clone or update.

That's particularly important for me because I'm a *long* way from
the US or Europe and cloning from scratch over the internet takes a
long time and suck up a lot of bandwidth. I don't even allow my test
machines to access the internet - they only know about the local
network and mirrors. I'd have to overide the fio submodule URL in
the xfstests repository on every test machine, and that gets messy
in a hurry.

Also, we distribute xfstests as a tarball, and there has been talk of
proper packaging (rpm/deb) as well. In those cases, the git
submodule approach does not work as we have to depend on the distro
supplied fio packages...

> (C1) Is not big deal in case of Fio because we already depends from
> libaio.

There's also a fio version dependency. i.e. _require_fio has to
detect whether the currently installed fio is of sufficiently recent
version for the tests to run.

> (P2) Makes xfstest coverage larger because all new tests which use new 
>      submodules functionality will start to work by default (today it
>       silently ignored). As i already told fio is under rapid
>      development Jens Axboe does very good job so (P2) really works for
>      me, new features i need for xfstets was reviewed and accepted by Jens
> http://git.kernel.dk/?p=fio.git;a=commit;h=8b28bd41375930664a0ff9ff9b101a88ac416ac5
> http://git.kernel.dk/?p=fio.git;a=commit;h=9c25d2e3f498707c4fd5a4bb0adf9867ecb17768
> http://git.kernel.dk/?p=fio.git;a=commit;h=e615ceafbe3962a35b7a7e06a0c8f4e2c0652c65

For me, that's not a "pro" - that's a "con" as i explained above.

> > (I package fio for Fedora, is it not commonly available on other
> > distros?)

Available for Debian, which means all it's derivatives also have it.

In short, I'd prefer we continue to use package level dependencies
detected through configure/_require_foo infrastructure than using
source tree level dependencies. Package level dependencies are much,
much easier to manage for most people and don't require everyone to
have internet access on the machines that xfstests is being built
on....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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