Date: Mon, 21 Nov 2011 03:09:23 +0400 From: Solar Designer <solar@...nwall.com> To: john-users@...ts.openwall.com Subject: Re: OpenMP not using all threads On Sun, Nov 20, 2011 at 03:21:16PM -0700, Stephen John Smoogen wrote: > Most (if not all) Linode systems are virtualized systems Yes. > which I believe normally don't do well with hyperthreading. I think you're wrong about this. What I think Linode actually does here is limit the customer's use of CPU time through giving them only 4 out of probably 16 logical CPUs (in a dual quad-core Xeon machine). Due to hyperthreading, these 4 actually let the customer use up to approximately 40% of the 8 physical cores' performance. If they gave the customer 8 logical CPUs, this would allow this single customer to almost fully (85% or so) use _both_ Xeon CPUs installed in the machine (as long as there's otherwise-idle CPU time), which Linode might not want to offer (or not at the same price). > For high compute > virtualization you usually need systems with cpu-pinning and such to > get the performance that you get from bare metal. CPU pinning is not that important for these machines and software. Alexander
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