Date: Mon, 29 Aug 2011 11:24:08 -0600 From: Brett Glass <brett@lariat.net> To: questions@freebsd.org Subject: Turn off hyperthreading on dual core Atom? Message-ID: <201108291724.LAA18734@lariat.net>
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I'm building a few systems using dual core Atom processors, and have noted that when the system boots up it says it has four CPUs: 2 actual cores and 2 virtual ones. But performance is a bit unsteady, and I'm wondering if it's going to be better to turn hyperthreading off. With hyperthreading, the FreeBSD scheduler simply acts as if there are 4 CPUs. Each "CPU" gets clock interrupts (which add overhead), and the scheduler is naive about the fact that two of the "CPUs" are not separate chips and could be held up if its mate has a heavy load. I do not know if the supposed higher utilization of the resources on each chip (including executing one thread while the CPU waits for data for another) is worth it. What has your experience been? --Brett Glass
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