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[log in to unmask]" type="cite">Hi
AthenaMP, ATLAS multi-process software is being designed to use any number of cores. However all the ATLAS multi-core queues setup across the grid so far have been configured to specify 8 cores.
While I am afraid I cannot find the documentation to back it up I believe the WLCG 'agreed' that experiments should be able to request 4n cores (where n is an integer). Even if this wasn't agreed I believe this is what ATLAS have adopted and for the moment are happy with 8 cores. I cannot predict what ATLAS will do with certainty but for those sites that primarily support ATLAS, if they were going to look into multi-core jobs, I would suggest working on ways to dynamically allocate 8 core jobs when ATLAS occasionally need them, rather than setup a dedicated whole node queue with dedicated resources. The dynamic job allocation was one of the requirements we look at when choosing HTCondor.
Anyway it is certainly something to discuss at a technical meeting!
Alastair
On 19 Sep 2013, at 11:21, Sam Skipsey <[log in to unmask]> wrote:
On 19 September 2013 10:48, Christopher J. Walker <[log in to unmask]> wrote:
On 19/09/13 10:12, Andrew Lahiff wrote:I believe it is perfectly possible to do this with CREAM too (though I'm not sure we have it set up on all CEs.
Hi,
For the record, for the new batch system at RAL we have multicore queues
on our CREAM CEs (currently configured to use 8 cores). However, on the
ARC CEs jobs can request exactly how many cores (and how much memory)
they need rather than having to use a specific queue.
Sure, it's basically how our MPI support works at Glasgow, IIRC, and we're entirely behind CREAM CEs.IIRC, when I asked the experiments why this wasn't sufficient and they wanted to auto discover how big the slot they had got was, it was because on a 12 core node, if you have jobs requesting 8 slots, they may actually end up on a 12 slot machine - and if they know this they can make use of the extra slots they discover they have.
Well, this is the difference between "whole node queues" and "multicore queues" (and between shared memory multicore queues and message passing multicore queues). Our MPI support provides precisely that - so a job can request any number of cores and it'll get them, but almost never all on the same node, as they don't need to be for MPI.(This seems sufficient for biomed, and indeed any other entity that writes MPI-based code.)
We don't support OpenMP style shared-memory parallelism where you require N slots all on the same node. (This makes the scheduling problem harder as has been discussed before.)
ATLAS/CMS seem to want whole node queues, in which case, if you assume a whole node queue is sensible a priori, it is reasonable for them to want to know how big the node they'll get is in advance.(This would be particularly pessimal for an 8 slot job arriving on a 64 slot node, for example.)We did have a whole node queue at Glasgow for testing (Andy Washbrook used this), but the scheduling was exceedingly pessimal (as running 10 jobs would offline 10 nodes, without checking how big the nodes were first... so if it hit a 64 core node...) so we turned it off.
SamChris
This is how both
ATLAS and CMS are running multicore jobs at RAL now. Condor is then
responsible for scheduling the mix of single and multicore jobs.
Regards,
Andrew.
-----Original Message-----
From: Testbed Support for GridPP member institutes [mailto:[log in to unmask]] On Behalf Of Alessandra Forti
Sent: 19 September 2013 09:57
To: [log in to unmask]
Subject: Re: Technical Meetings
Well that's for testing. If it goes in production it will be more than one node and most of the things that are keeping this back are operational i.e. how not to waste resources and how to do the accounting if a job requests a certain number of CPU or the whole node.
cheers
alessandra
On 18/09/2013 18:18, Christopher J. Walker wrote:
On 18/09/13 17:22, David Colling wrote:
Hi Alessandra,QMUL now has a single node MPI queue - Dan has more details. What more
Yes they are indeeedee. I only know of bits and pieces in the LHC
world but do know, for example, that our T2K colleagues make
extensive use of them. The Imperial T2K people code and debug locally
and then run on the RAL resources. This is proving so successful that
we are considering adding a bigger node - perhaps to the GridPP
cloud so that others could use it via OpenStack. These are at the
*ideas* stage at the moment, but if we did would there be any takers
or would we have just thrown away a chunk of money (or rather given
it to T2K as I am sure that they would use them)?
I guess that the question is what should GridPP be doing about this?
I don't see it as our place to fund development in the individual
experiments but should we be acting as a conduit for best practise?
Organising Goofit tutorials? Interacting with EGI as Stephen suggests?
What else? Is there a focus that we can develop with very little money?
I think that these are questions for next Tuesday rather than Friday
but I will add a specific discussion to the discussion agenda for this.
does one need?
Chris
Best,
david
On 18/09/13 14:41, Alessandra Forti wrote:
Hi,
multicore should become a reality at the end of LS1. We should
definitely have it as an activity.
cheers
alessandra
On 18/09/2013 14:12, David Colling wrote:
Hi,
I am just drawing up an agenda and is it worth having an item on
FTS3 (from Andrew L.)?
Also the many and multicore activity. Is somebody able to describe
what has been happening in these two areas? Is this something that
we want to have as an activity in GridPP5?
Best,
david
--
Facts aren't facts if they come from the wrong people. (Paul Krugman)
-- Facts aren't facts if they come from the wrong people. (Paul Krugman)