[Beowulf] HPC workflows

John Hearns hearnsj at googlemail.com
Wed Nov 28 04:54:53 PST 2018

MArk, again I do not have time to give your answer justice today.
However, as you are in NL, can you send me some olliebollen please? I am a
terrible addict.

On Wed, 28 Nov 2018 at 13:52, mark somers <m.somers at chem.leidenuniv.nl>

> Well, please be careful in naming things:
> http://cloudscaling.com/blog/cloud-computing/grid-cloud-hpc-whats-the-diff/
> (note; The guy only heard about MPI and does not consider SMP based codes
> using i.e. OpenMP, but he did understand there are
> different things being talked about).
> Now I am all for connecting divers and flexible workflows to true HPC
> systems and grids that feel different if not experienced
> with (otherwise what is the use of a computer if there are no users making
> use of it?), but do not make the mistake of thinking
> everything is cloud or will be cloud soon that fast.
> Bare with me for a second:
> There are some very fundamental problems when dealing with large scale
> parallel programs (OpenMP) on virtual machines (most of
> the cloud). Google for papers talking about co-scheduling. All VM
> specialists I know and talked with, state generally that using
> more than 4 cores in a VM is not smart and one should switch to bare metal
> then. Don't believe it? Google for it or just try it
> yourself by doing a parallel scaling experiment and fitting Amdahls law
> through your measurements.
> So, one could say bare metal cloud have arisen mostly because of this but
> they also do come with expenses. Somehow I find that a
> simple rule always seems to apply; if more people in a scheme need to be
> paid, the scheme is probably more expensive than
> alternatives, if available. Or state differently; If you can do things
> yourself, it is always a cheaper option than let some
> others do things (under normal 'open market' rules and excluding the
> option of slavery :)).
> Nice read for some background:
> http://staff.um.edu.mt/carl.debono/DT_CCE3013_1.pdf
> One has to note that in academia one often is in the situation that grants
> are obtained to buy hardware and that running costs
> (i.e. electricity and rack space) are matched by the university making the
> case of spending the grant money on paying amazone or
> google to do your 'compute' not so sensible if you can do things yourself.
> Also given the ease of deploying an HPC cluster
> nowadays with OpenHPC or something commercial like Qlustar or Bright, it
> will be hard pressed to justify long term bare metal
> cloud usage in these settings.
> Those were some technical and economical considerations that play a role
> in things.
> There is also another aspect when for example dealing with sensitive data
> you are to be helt responsible for. The Cloud model is
> not so friendly under those circumstances either. Again your data is put
> "on someone else's computer". Thinking of GDPR and
> such.
> So, back to the point, some 'user driven' workloads might end up on clouds
> or on bare-metal on-premisse clouds (seems to be the
> latest fad right now) but clearly not everything. Especially if the
> workloads are not 'user driven' but technology (or
> economically or socially driven) i.e. there is no other way of doing it
> except using some type of (specialized) technology (or
> it is just not allowed). I therefore also am of opinion that cloud
> computing is also not true (traditional) HPC and that the
> term HPC has been diluted over the year by commercial interest / marketing
> speak.
> BTW, on a side note / rant; The mathematics we are dealing with here are
> the constraints to be met in optimising things. The
> constraints actually determine the final optimal case (
> https://en.wikipedia.org/wiki/Lagrange_multiplier) and people tend to
> 'ignore' or not specify the constraints in their arguments about what is
> the best or optimal thing to do. So what I did here is
> I have given you some example of constraints (technical, economical and
> social) in the 'everything will be cloud' rhetoric to
> keep an eye on before drawing any conclusions about what the future might
> bring :).
> just my little opinion though...
> Disclaimer; I could be horribly wrong :).
> --
> mark somers
> tel: +31715274437
> mail: m.somers at chem.leidenuniv.nl
> web:  http://theorchem.leidenuniv.nl/people/somers
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