Date: Fri, 5 Mar 2010 22:14:50 -0600 From: Kevin Day <toasty@dragondata.com> To: freebsd-hackers@freebsd.org Subject: ACPI/power implementation causing performance loss with i7/Nehalem turbo boost Message-ID: <0ECDEB94-E60E-45C7-98AC-5E948DE4649C@dragondata.com>
next in thread | raw e-mail | index | archive | help
Recently I bumped into something very weird. In some CPU heavy = workloads, FreeBSD ran faster inside VMware's ESX hypervisor than it did = running natively on bare metal. Simple pure CPU applications (such as = "openssl speed") would run 10-30% faster on VMware. This seemed very = counterintuitive, until I discovered what I believe to be the cause.=20 Intel Nehalem and i5/i7 processors have a feature called "Turbo Boost", = where the more cores that are inactive (ACPI states C2 or C3) the higher = the clock rate of the active cores. In some processors increasing the = clock speed by more than 1ghz. On a hunch, I disabled turbo boost = (through the BIOS) on our ESX system, and this brought the speeds back = on par with the bare metal FreeBSD box. So, it seems that the VMware hypervisor is deactivating cores on the CPU = when idle, but FreeBSD itself isn't. Is anyone working on giving = FreeBSD's idle loop/scheduler the ability to go into deeper sleep = states? It seems this would have more than just a power savings benefit = now. Intel documentation on Turbo Boost: = http://download.intel.com/design/processor/applnots/320354.pdf?iid=3Dtech_= tb+paper -- Kevin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?0ECDEB94-E60E-45C7-98AC-5E948DE4649C>