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:	Wed, 13 May 2015 09:25:39 +0200
From:	Pavel Machek <pavel@....cz>
To:	Daniel Phillips <daniel@...nq.net>
Cc:	Howard Chu <hyc@...as.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	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 Mon 2015-05-11 16:53:10, Daniel Phillips wrote:
> Hi Pavel,
> 
> On 05/11/2015 03:12 PM, Pavel Machek wrote:
> >>> It is a fact of life that when you change one aspect of an intimately interconnected system,
> >>> something else will change as well. You have naive/nonexistent free space management now; when you
> >>> design something workable there it is going to impact everything else you've already done. It's an
> >>> easy bet that the impact will be negative, the only question is to what degree.
> >>
> >> You might lose that bet. For example, suppose we do strictly linear allocation
> >> each delta, and just leave nice big gaps between the deltas for future
> >> expansion. Clearly, we run at similar or identical speed to the current naive
> >> strategy until we must start filling in the gaps, and at that point our layout
> >> is not any worse than XFS, which started bad and stayed that way.
> > 
> > Umm, are you sure. If "some areas of disk are faster than others" is
> > still true on todays harddrives, the gaps will decrease the
> > performance (as you'll "use up" the fast areas more quickly).
> 
> That's why I hedged my claim with "similar or identical". The
> difference in media speed seems to be a relatively small effect

When you knew it can't be identical? That's rather confusing, right?
Perhaps you should post more details how your benchmark is structured
next time, so we can see you did not make any trivial mistakes...?

Or just clean the code up so that it can get merged, so that we can
benchmark ourselves...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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