blade servers (was Re: [Bioclusters] Any experiences with these guys? reeks)

[Tim Cutts]

On 04-Nov-03, Ognen Duzlevski wrote:
> Could someone educate me on the importance of turning off hyperthreading?
> I guess I've been sleeping in the past several months...

Current Linux kernels don't know how to schedule to it; they see four
distinct CPUs.  If you run two single threaded jobs on a machine with
hyperthreading enabled, it's possible that that the scheduler will
decide to put both on the same physical CPU, and leave the other one
free.  This will not happen if hyperthreading is disabled, and each job
will get a physical CPU to itself.

So, if you run multithreaded code exclusively, or predominantly, switch
hypethreading on.  If you principally run single threaded jobs, switch
it off, until such time as you're running a kernel with a scheduler
which understands hyperthreading (I believe there are some patches to do
this, now)

Tim

-- 
Dr Tim Cutts
Informatics Systems Group
Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK