Set cpu count how ?


log in

Advanced search

Questions and Answers : Unix/Linux : Set cpu count how ?

Author Message
Profile David Anderson (not *that* DA)
Avatar
Send message
Joined: 5 Dec 09
Posts: 103
Credit: 20,845,296
RAC: 20,738
United States
Message 1070921 - Posted: 26 Jan 2011, 21:10:10 UTC

Just a random David A volunteer, not 'the' David A.

With Hyperthreading turned on Linux reports
the CPU count higher than it really is.
(Xeon 5670, 2 cpus, 6 cores each shows
as 24, not 12 in /proc/cpuinfo, so boinc
starts too many processes for best cpu use)
(This is a new machine, just going into service).

This issue is known in Linux kernel discussions
(google found one in 2006) but it is not really
considered a bug.

I'll bet there is a simple way to put some xml
somewhere that will let me set the cpu count
boinc projects (like Seti, Einstein) see
as the cpu count.

Thanks in advance for any suggestions.
____________

Profile Gundolf Jahn
Send message
Joined: 19 Sep 00
Posts: 3184
Credit: 354,976
RAC: 22
Germany
Message 1070925 - Posted: 26 Jan 2011, 21:29:49 UTC - in response to Message 1070921.

Try setting "On multiprocessors, use at most 50% of the processors" in your Computing preferences (or corresponding in local preferences).

Greets,
Gundolf (There's no "sharp s" on a Spanish keyboard:-)

Profile David Anderson (not *that* DA)
Avatar
Send message
Joined: 5 Dec 09
Posts: 103
Credit: 20,845,296
RAC: 20,738
United States
Message 1070939 - Posted: 26 Jan 2011, 22:09:52 UTC

A Dual-Core processor machine has no BIOS option letting me
chose hyperthreading (Linux /proc/cpuinfo shows 'ht' in
the flags, so I think the cpu has hyperthreading. Maybe.)

The (new) 12 core machine BIOS has hyperthreading as an option.

So I guess I either turn off hyperthreading on the 12 core machine
or I live with only 1 cpu (50%) on the 2 core machine,
or I just let things run as they are. I wonder which
would give the best WU production (but it could take a long time
to figure out... and at least with present settings all cpus
are busy... so for now I'll just let things run and watch for
anything odd).
[Ignoring the possibility of updating BIOS/firmware on the 2-core machine...]

Thanks for the prompt response. Much appreciated!
____________

Profile arkayn
Volunteer tester
Avatar
Send message
Joined: 14 May 99
Posts: 3544
Credit: 46,236,174
RAC: 31,468
United States
Message 1070967 - Posted: 26 Jan 2011, 23:43:16 UTC

Yes the X5670 does have hyperthreading so it is 6 cores/12 logical threads per CPU. As you have 2 of them that does equal 24 processors to BOINC.
____________

Profile Gundolf Jahn
Send message
Joined: 19 Sep 00
Posts: 3184
Credit: 354,976
RAC: 22
Germany
Message 1071090 - Posted: 27 Jan 2011, 8:12:42 UTC - in response to Message 1070939.

So I guess I either turn off hyperthreading on the 12 core machine
or I live with only 1 cpu (50%) on the 2 core machine...

If you use the local preferences, only that machine is affected where you set them.

Gundolf

Profile David Anderson (not *that* DA)
Avatar
Send message
Joined: 5 Dec 09
Posts: 103
Credit: 20,845,296
RAC: 20,738
United States
Message 1071164 - Posted: 27 Jan 2011, 16:43:49 UTC

Ah. My goodness. The boinc-gui is perfectly clear on its
preferences page that the preferences are for
that computer only, but somehow the message did not penetrate
my brain.

Thank you Gundolf Jahn for gently pointing out I had
missed the obvious.

So now running 12 cores on the new machine.

Interestingly having cut down the process count boinc runs
from 24 to 12 resulted in the wattage decreasing by 30 watts.
It is two systems on a meter (not just the one system)
but the overall wattage decreased from 560 to 530 with that
one change.

The question arkayn raises in my head is whether I'll get more
WU production with 24 processes running or with 12.
Is the answer well known and certain? Or does it depend
on other things?

Thanks again folks.

____________

Profile David Anderson (not *that* DA)
Avatar
Send message
Joined: 5 Dec 09
Posts: 103
Credit: 20,845,296
RAC: 20,738
United States
Message 1071172 - Posted: 27 Jan 2011, 17:07:29 UTC

A forum search for 'hyperthread' turned up lots of interesting info.
But no firm answer. For now I am leaving hyptherthead on but
restricting to 50% so each of the 12 cores has one task.

Any and all suggestions are welcome.
____________

Questions and Answers : Unix/Linux : Set cpu count how ?

Copyright © 2014 University of California