linux-kernel - Re: xfs: does mkfs.xfs require fancy switches to get decent performance? (was Tux3 Report: How fast can we fsync?)

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Message-ID: <1430404405.3180.152.camel@gmail.com>
Date:	Thu, 30 Apr 2015 16:33:25 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Daniel Phillips <daniel@...nq.net>
Cc:	Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	Theodore Ts'o <tytso@....edu>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: xfs: does mkfs.xfs require fancy switches to get decent
 performance? (was Tux3 Report: How fast can we fsync?)

On Thu, 2015-04-30 at 07:07 -0700, Daniel Phillips wrote:
> 
> On 04/30/2015 06:48 AM, Mike Galbraith wrote:
> > On Thu, 2015-04-30 at 05:58 -0700, Daniel Phillips wrote:
> >> On Thursday, April 30, 2015 5:07:21 AM PDT, Mike Galbraith wrote:
> >>> On Thu, 2015-04-30 at 04:14 -0700, Daniel Phillips wrote:
> >>>
> >>>> Lovely sounding argument, but it is wrong because Tux3 still beats XFS
> >>>> even with seek time factored out of the equation.
> >>>
> >>> Hm.  Do you have big-storage comparison numbers to back that?  I'm no
> >>> storage guy (waiting for holographic crystal arrays to obsolete all this
> >>> crap;), but Dave's big-storage guy words made sense to me.
> >>
> >> This has nothing to do with big storage. The proposition was that seek
> >> time is the reason for Tux3's fsync performance. That claim was easily
> >> falsified by removing the seek time.
> >>
> >> Dave's big storage words are there to draw attention away from the fact
> >> that XFS ran the Git tests four times slower than Tux3 and three times
> >> slower than Ext4. Whatever the big storage excuse is for that, the fact
> >> is, XFS obviously sucks at little storage.
> > 
> > If you allocate spanning the disk from start of life, you're going to
> > eat seeks that others don't until later.  That seemed rather obvious and
> > straight forward.
> 
> It is a logical falacy. It mixes a grain of truth (spreading all over the
> disk causes extra seeks) with an obvious falsehood (it is not necessarily
> the only possible way to avoid long term fragmentation).

Shrug, but seems it is a solution, and more importantly, an implemented
solution.  What I gleaned up as a layman reader is that xfs has no
fragmentation issue, but tux3 still does.  It doesn't seem right to slam
xfs for a conscious design decision unless tux3 can proudly display its
superior solution, which I gathered doesn't yet exist.

> > He flat stated that xfs has passable performance on
> > single bit of rust, and openly explained why.  I see no misdirection,
> > only some evidence of bad blood between you two.
> 
> Raising the spectre of theoretical fragmentation issues when we have not
> even begun that work is a straw man and intellectually dishonest. You have
> to wonder why he does it. It is destructive to our community image and
> harmful to progress.

Well ok, let's forget bad blood, straw men... and answering my question
too I suppose.  Not having any sexy  IO gizmos in my little desktop box,
I don't care deeply which stomps the other flat on beastly boxen.

	-Mike

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