Date: Tue, 20 Sep 2011 22:28:18 +0100 From: Richard Collyer <richard@blueapex.co.uk> To: freebsd-questions@freebsd.org Subject: Re: How can I disable hyperthreads, but NOT smp ? Message-ID: <4E790572.10602@blueapex.co.uk> In-Reply-To: <1316550882.13474.YahooMailClassic@web121217.mail.ne1.yahoo.com> References: <1316550882.13474.YahooMailClassic@web121217.mail.ne1.yahoo.com>
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On 20/09/2011 21:34, Jason Usher wrote: > FreeBSD 6.4-RELEASE system with two physical CPUs, each of which are HT capable. From dmesg: > > cpu0 (BSP): APIC ID: 0 > cpu1 (AP): APIC ID: 1 > cpu2 (AP): APIC ID: 6 > cpu3 (AP): APIC ID: 7 > > I also see this: > > machdep.hyperthreading_allowed: 0 > > The problem is, I have reason to believe that my workload benefits greatly from SMP, but is not playing nicely with hyperthreading. That is, it is trying to farm out 4 things at a time to a cpu setup that really is only able to do two things at a time. > > How can I disable HT completely, but still retain ALL the benefits of SMP ? > > Thanks. It's usually a setting in the BIOS to disable Hyperthreading then reconfigure the kernel to only use 2 cores (which it might do automatically). Hyperthreading is outside the world of FreeBSD. As far as it knows there is still 4 "logical processors". Disabling hyperthreading it should see 2 LPs. Richard -- Richard Collyer Blue Apex Ltd 07900 997 380 Registered as a company in England and Wales (Reg Number: 05982514). Registered Address: 42 King Richards Hill, Earl Shilton, Leicester, LE9 7EY __________ Information from ESET NOD32 Antivirus, version of virus signature database 6480 (20110920) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com
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