Date: Mon, 23 Feb 2009 10:39:38 -0800 From: Maxim Sobolev <sobomax@FreeBSD.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: Frank Behrens <frank@ilse.behrens.de>, Jeff Roberson <jeff@FreeBSD.org>, "current@freebsd.org" <current@FreeBSD.org>, stable@FreeBSD.org Subject: Re: The machdep.hyperthreading_allowed & ULE weirdness in 7.1 Message-ID: <49A2ED6A.9040202@FreeBSD.org> In-Reply-To: <alpine.BSF.2.00.0902231801450.92010@fledge.watson.org> References: <alpine.BSF.2.00.0902231000300.98609@fledge.watson.org> <200902231652.n1NGqMxH047731@post.behrens.de> <49A2DE9D.4090902@FreeBSD.org> <alpine.BSF.2.00.0902231801450.92010@fledge.watson.org>
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Robert Watson wrote: > In the mean time, it sounds like the sysctl does need to be > reimplemented or removed, but one question is how far to take it -- > caches are shared to varying degrees at varying levels of the topology. > However, I believe the recommendation has generally moved to disabling > hyperthreading using the BIOS, as that uses the vendor's notion of > hyperthreading. The idea of changing the setting at run-time is > currently untenable because we don't have the OS infrastructure to take > CPUs out of service, although growing it would be useful in order to > support virtual machine dynamic CPU reconfiguration. Well, as far as I know, what SCHED_4BSD does is simply stopping scheduling threads to the logical core(s). One doesn't need infrastructure to take CPU off-line for doing the same in SCHED_ULE. Unfortunately access to BIOS is not always an option and also some BIOSes don't even provide a feature to turn HTT off. -Maxim
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