Messages in this thread | | | Date | Wed, 28 Oct 2009 22:24:39 +0000 | From | Alan Cox <> | Subject | Re: Hyperthreading on 4 core CPU DECREASES performance??? |
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> This is Ubuntu Hardy, 2.6.24 kernel. I tried the same with 2.6.31, > with the same effect. > > This article from Intel: > > http://software.intel.com/sites/oss/pdfs/mclinux.pdf > > It talks about intelligent handling of multiple cores as a done deal, > but in my experience that did not actually occur. > > I would like to know how can I make the scheduler to prefer to spread > the tasks across physical cores as opposed to bundling two on one core > and leaving some cores idle.
The scheduler will try and do balancing for packages and for HT. Make sure your distribution is built with the SCHED_SMT and SCHED_MC options enabled. Some of the non-enterprise distirbutions may well not have these enabled.
For hand laying out threads see: man pthread_setaffinity_np
The win from HT depends a lot on the CPU and also the workload mix. In some workloads it will decrease performance.
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