1) Message boards : LHC@home Science : Collision energies (Message 49951)
Posted 3 days ago by Henry Nebrensky
Post:
Thanks for that - I'll have to read it through properly.
It's nice to see LHC experiments other than the big four get a mention.

For reference., p21 answers a similar question I think: Lead-Lead has a total of 1150 TeV available but there is actually only 5.02 TeV available to the colliding pair of nucleons within; possibly I'm misunderstanding the physics but shouldn't there be a similar downshift between the overall proton(nucleon) energy and that of the actual colliding constituents?
2) Message boards : LHC@home Science : Collision energies (Message 49898)
Posted 13 days ago by Henry Nebrensky
Post:
Hi all,

Does anybody here know roughly what the maximum "physics energy" is for an LHC proton-proton collision?

Since protons are composite particles the collisions are actually between individual quarks/gluons/whatever, and I'd like to get an idea of the "inefficiency" compared to the beam proton energy.

I couldn't see this in a quick look at Wikipedia, probably because I'm not sure what the technical terms would be!

Thanks
3) Message boards : Cafe LHC : Eviction of Russian scientists (Message 48897)
Posted 4 Nov 2023 by Henry Nebrensky
Post:
(Who's "we"?)
That's odd considering we welcome doctors from India/Pakistan.
Only because they accept NHS pay rates...

So scientists aren't considered important?
No - (foreign) scientists are just as much seen as cheap exploitable disposable labour. That's why the UK Government's R&D people and culture strategy avoids any commitment to retaining experienced staff or supporting returns after a career break, but when it comes to getting in naive junior staff there's bullet points a-plenty!
4) Message boards : Cafe LHC : CMS: I'm (almost) back (Message 48896)
Posted 4 Nov 2023 by Henry Nebrensky
Post:
Hi Ivan, glad to hear you've made it home at last...

I've been trying to arrange another trip into London to visit en route, but not been able to stitch (geddit!) all the various stop-offs needed together :(

Focus on your recovery!
5) Message boards : Theory Application : How long may Native-Theory-Tasks run (Message 48154)
Posted 30 May 2023 by Henry Nebrensky
Post:
Theory native logs can be checked, e.g for a task running in slot 0
.../slots/0/cernvm/shared/runRivet.log

If you "head" the runRivet.log, it will tell you the code in use and how many events that specific task is to generate:
[boinc pp jets 8000 170,-,2960 - pythia8 8.301 dire-default 57000 482]
57k in this case. If you then "tail" the log you can see how far it's got and if it's making progress...
6) Message boards : LHC@home Science : Ready to restart! (Message 47245)
Posted 12 Sep 2022 by Henry Nebrensky
Post:
It looks like they are indeed training the magnets these days, there are magnet quenches with no beam.
Possibly, but given the potential side-effects of a quench - remember those magnets scattered around the tunnel after the first startup - I know I would be wary of trying to train to 14TeV current settings before getting 13TeV data in the can. I'm intrigued by the cryptic references to UFOs in that blog post - sounds suspiciously like someone's dropping their spanners on the machine. (Unless that's a dated baguette reference?)
7) Message boards : LHC@home Science : Ready to restart! (Message 47195)
Posted 27 Aug 2022 by Henry Nebrensky
Post:
Meanwhile the LHC magnets remain at 2K, allowing more time to train the magnets.
What does that involve?
8) Message boards : LHC@home Science : Proton Physics : Stable Beams (Message 47054)
Posted 30 Jul 2022 by Henry Nebrensky
Post:
Why does the luminosity at an experiment's IP vary relative to the circulating beam? (e.g. what happened at Alice before/after 20:00-ish?)

Does this mean that the LHC dynamically alters the lattice even within a fill?
9) Message boards : Theory Application : Sherpa tasks run okay for long time, then they fail (Message 47024)
Posted 15 Jul 2022 by Henry Nebrensky
Post:
7.100 events (8d 17h) atm.
But isn't that going to take more like 14 days to complete, rather than 10?
10) Message boards : Number crunching : CentOS9 squid Win11pro (Message 46857)
Posted 8 Jun 2022 by Henry Nebrensky
Post:
CentOS8 have no Mirror, out of support since 2022/01.
As announced a couple of years ago, CentOS became "CentOS Stream". Conversion instructions for CentOS8 to CentOS Stream8 are at https://www.centos.org/centos-stream/.
(I've not tried them; I've been reverting to C7 instead).
11) Questions and Answers : Getting started : How To Setup VirtualBox With LHC@HOME On Command Line Only Server? (Message 46645)
Posted 15 Apr 2022 by Henry Nebrensky
Post:
I got some cloud VMs and want to contribute to the project, but the native applications always fail, and I couldn't fix it. I am wondering how can I setup VirtualBox with LHC.
As these are already VMs, I doubt Virtualbox will run correctly inside them. Never tried it though.

I did simply `sudo apt install virtualbox -y`, is that all?

Answering the subject line, my old notes for CentOS7/8 (Minimal install) say:

    VBox needs gcc, make, elfutils-libelf-devel, kernel-devel and kernel-headers; not a dependency in the RPM. May also need: setools-libs libsemanage-python
    yum install gcc make elfutils-libelf-devel kernel-devel  kernel-headers setools-libs libsemanage-python libseccomp

    Install the downloaded VirtualBox RPM:
    yum localinstall VBox-version.RPM

    user running BOINCmust be in VBox group:
    usermod --append --groups vboxusers boinc

    Rebuild the kernel modules:
    vboxconfig

    Start VBox services:
    service vboxautostart-service start
service vboxdrv restart

    Optional:
    VBoxManage extpack install /tmp/Oracle_VM_VirtualBox_Extension_Pack-version.vbox-extpack


All as root, via SSH. That should should give a working VirtualBox testable by restarting the BOINC client.
If working, remember to chkconfig the services on before rebooting.
When updating the kernel, remember to re-run vboxconfig to build the new modules before rebooting.

Other useful bits:

VBoxManage list extpacks

VBoxManage list vms
VBoxManage showvminfo 1e6cf289-3176-476f-b80c-6fa3fbe42922
VBoxManage unregistervm 1e6cf289-3176-476f-b80c-6fa3fbe42922 --delete


Distro-specific and SysV-to-systemd translation left as an exercise for the reader.

Note that I've not tested this in a couple of years as I don't have any suitable machine at the moment. Any problems see Yeti's Checklist
12) Message boards : Number crunching : CentOS9 (Message 46488)
Posted 20 Mar 2022 by Henry Nebrensky
Post:
Mirror for CentOS8 is out of Service since 22/01/31.
Isn't that part of the change from CentOS to CentOS Stream? This has caused some "discussion" in the community, including proposals for LHC to move away from CentOS to some other distro. I don't know if there's any clear route on this yet.

CVMFS is not supported for CentOS9 (only CentOS7 and CentOS8).
May well be low-priority due to above.
13) Message boards : ATLAS application : Atlas task slowing right down near the end but still using all cores - continue? (Message 46414)
Posted 3 Mar 2022 by Henry Nebrensky
Post:
I would vote for 240.
Actually, I'd vote for 360 - them Babylonians knew what they were doing ...
Are they the ones responsible for clocks?
... and angles, (which is where clock faces came from?).
But, actually computezrmle was right: 240 also gets you a division by 16, for future expansion.
14) Message boards : ATLAS application : Atlas task slowing right down near the end but still using all cores - continue? (Message 46403)
Posted 2 Mar 2022 by Henry Nebrensky
Post:
I would vote for 240.
Actually, I'd vote for 360 - them Babylonians knew what they were doing - but if people are already struggling with compute times then it would be better to stick to low hanging fruit. :(
15) Message boards : ATLAS application : Atlas task slowing right down near the end but still using all cores - continue? (Message 46402)
Posted 2 Mar 2022 by Henry Nebrensky
Post:
Even within a task, as the number of threads is reduced then each thread must run more events, and it's more likely - but not guaranteed - that they will average out across the threads.
Even with the full 8 cores, that's 25 events per thread, which is more than enough to average things out.
Doesn't that depend on the variance, which I've never studied? In any case, the aim is that the averaging overcomes the variance, which is why divisibility is important for avoiding a small number of events left over.

Also, do you have a figure for how much time is wasted? Since it's 200 in the pool, the wasted cores at the end are probably a fraction of a percent of inefficiency.
IIRC, back when I was running 8-core native Atlas I would generally see the active threads reduce over usually 1-2 minutes, 5 if slow, for tasks of about 4 hrs total wall-clock. (There might be numbers in some ancient post here, but the laptop's tired tonight :( )
A few minutes in 4 hours is nothing.
Thank you - I did put some effort into setting those machines up...
16) Message boards : ATLAS application : Atlas task slowing right down near the end but still using all cores - continue? (Message 46399)
Posted 2 Mar 2022 by Henry Nebrensky
Post:
... they are random sizes.
You are looking on just 1 task but you would have to look at the long term averages.
Really huge numbers!
... I'm surprised there's a difference though, considering the wide variance in event times.
Even within a task, as the number of threads is reduced then each thread must run more events, and it's more likely - but not guaranteed - that they will average out across the threads.

Was the wide variance I saw unusual?
I've no idea.

Also, do you have a figure for how much time is wasted? Since it's 200 in the pool, the wasted cores at the end are probably a fraction of a percent of inefficiency.
IIRC, back when I was running 8-core native Atlas I would generally see the active threads reduce over usually 1-2 minutes, 5 if slow, for tasks of about 4 hrs total wall-clock. (There might be numbers in some ancient post here, but the laptop's tired tonight :( )
17) Message boards : ATLAS application : Atlas task slowing right down near the end but still using all cores - continue? (Message 46390)
Posted 1 Mar 2022 by Henry Nebrensky
Post:
As CP mentioned each ATLAS task processes 200 events from a pool.
It has struck me before, that changing the task's pool size to 180 or 240 events would give better divisibility.
18) Message boards : Sixtrack Application : Sixtrack BOINC application on track to be ported to GPUs? (Message 46205)
Posted 9 Feb 2022 by Henry Nebrensky
Post:
... and now SQUID. That is a lot to ask of volunteer crunchers.
Set up once, runs for months...
More to the point, you don't even need to start worrying about Squid until after you've been through the VirtualBox/CVMFS palaver at least once (to create useful traffic for a Squid to cache), and then only for the larger scale crunchers.
If Sixtrack becomes as painful to get running as, say, Atlas, then surely this will be a big turn-off when trying to encourage new, casual volunteers to join the project.
19) Message boards : Sixtrack Application : Sixtrack BOINC application on track to be ported to GPUs? (Message 46202)
Posted 9 Feb 2022 by Henry Nebrensky
Post:
I'm intrigued as to how the run-time compilation of C by a python app (p. 54 on) would translate to running on an arbitrary BOINC client, especially a Windows one.
Mmmmm, virtual machine?
But the big selling point of Sixtrack as a BOINC project is precisely that it Just Works, without all the shenanigans of VirtualBox or CVMFS or whatever...
20) Message boards : Sixtrack Application : Sixtrack BOINC application on track to be ported to GPUs? (Message 46188)
Posted 7 Feb 2022 by Henry Nebrensky
Post:
Just curious for XTrack (a part of the new XSuite) i find this pdf and the project seems to be ambitious (see page 15)...
I'm intrigued as to how the run-time compilation of C by a python app (p. 54 on) would translate to running on an arbitrary Boinc client, especially a Windows one.


Next 20


©2024 CERN