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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Date:	Thu, 30 Apr 2015 07:07:46 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
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 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).

> 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.

> No, I won't be switching to xfs any time soon, but then it would take a
> hell of a lot of evidence to get me to move away from ext4.  I trust
> ext[n] deeply because it has proven many times over the years that it
> can take one hell of a lot (of self inflicted wounds;).

Regards,

Daniel
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