SMP (Was: Why did you choose DragonFly?)

Samuel J. Greear sjg at
Mon Sep 20 15:26:04 PDT 2010

2010/9/20 Przemysław Pawełczyk <pp_o2 at>:
> On Mon, 20 Sep 2010 13:33:28 -0600
> "Samuel J. Greear" <sjg at> wrote:
>> This mail is intended for the infrequent responders and lurkers on the
>> list just as much as the regular posters.
>> What has drawn you to use the DragonFly BSD operating system and/or
>> participate in its development by following this list? Technical
>> features, methodologies, something about the community? I suspect the
>> HAMMER filesystem to be the popular choice, but what other features
>> affect or do you see affecting your day to day life as an
>> administrator, developer, or [insert use case here], now or in the
>> future?
> Hi Sam,
> A question for a question.
> Why _no one_ answered my question concerning DF BSD contained in my
> post:
> What did I do wrong?
> I thought them over before I gathered enough temerity to ask here for
> anything.
> Why do you ask me -"a lurker" - to answer your questions when you
> (plural) are treating "the lurkers" that way?
> Regards
> --
> Przemysław Pawełczyk (P2O2) [pron. Pshemislav Paveltchick]
>, pp_o2 at

I will try to answer here and now.

The purpose of my question(s) is because I believe DragonFly BSD is
not adequately represented in the easily accessible (main page and
pages directly linked from it) literature on our website. I would like
to fix this so that questions like yours need not arise in the future.
As a first step I wanted to learn what people like about DragonFly and
what keeps people using this OS and participating in the community so
that I could expand on those points.

DragonFly BSD is not necessarily targeted -to- SMP, rather it supports
SMP and adopts a slightly different model than other mainstream
operating systems. Most OS kernels use primarily "hard" locks in the
form of mutexes and spinlocks. DragonFly prefers "soft" locks in the
form of tokens and, even better, lockless algorithms. I do not believe
anyone is ready to make any bold claims about our current SMP
performance. However, I do believe many developers would claim that
even though we may be a bit behind in performance today our
model/methodology positions us well for the future.

Modern hardware should be pretty well supported, if FreeBSD supports
it then generally so should we and if we don't it is likely not too
much work to port that support over. Matt Dillon just brought up
DragonFly on a new AMD 880-series-based motherboard with a 6-core CPU
and that is apparently working quite well.

HAMMER is definitely a competitor to ZFS, although not in terms of
volume management. We have LVM for that, but currently it does not
support many of the targets one might expect (None of the real RAID
levels). HAMMER is partly MPSAFE and many of the subsystems above it
are also partially or fully MPSAFE, performance on multiple CPU's
should be quite good from the point of view of the filesystem.

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