Date: Mon, 23 Feb 2009 20:27:05 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Maxim Sobolev <sobomax@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: <alpine.BSF.2.00.0902232026180.92010@fledge.watson.org> In-Reply-To: <49A30456.5010400@FreeBSD.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> <49A2ED6A.9040202@FreeBSD.org> <alpine.BSF.2.00.0902231853040.92010@fledge.watson.org> <49A30456.5010400@FreeBSD.org>
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On Mon, 23 Feb 2009, Maxim Sobolev wrote: >>> Unfortunately access to BIOS is not always an option and also some BIOSes >>> don't even provide a feature to turn HTT off. >> >> It's not quite that simple -- in a world of device drivers pinning threads >> to CPUs for workload distribution, callout threads and >> sched_bind()/sched_pin() for crypto load distribution, etc, you need a >> whole infrastructure for software-disabled CPUs. Disabling it using the >> BIOS or device.hints is the only reliable way to do this right now. >> Changing the architecture of the kernel to disable CPU cores after boot is >> a significant investment of work, and as I mentioned elsewhere, it is >> disable to do this so that we can support dynamic reconfiguration in the >> presence of a hypervisor, but it's highly non-trivial. There may be some >> shortcuts that can be taken for policy reasons in the probing of CPUs when >> the topology is detected that avoid the full dynamic solution having to be >> done in the short-term, that in effect are a short-hand for device.hints >> entries, but I don't know to what extent the CPU topology from ACPI is >> available at the point where we'd need to know that. > > So, are you suggesting that we should disable machdep.hyperthreading_allowed > with ULE in 7.x and current to avoid confusion? Possibly even without ULE. Robert N M Watson Computer Laboratory University of Cambridge
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