Date: Tue, 04 Feb 2003 15:41:54 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: Brendon and Wendy <brendy33@attbi.com>, Chris Luke <chrisy@flix.net>, freebsd-smp@freebsd.org Subject: Re: mp_machdep.c patch Message-ID: <XFMail.20030204154154.jhb@FreeBSD.org> In-Reply-To: <3E4021D4.7D1FCD43@mindspring.com>
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On 04-Feb-2003 Terry Lambert wrote: > John Baldwin wrote: >> > You have to enable HT in the BIOS. If it is not enabled in the >> > BIOS, it will not add entries to the MP Table for the virtual >> > processors, and they will not be recognized. >> >> This is not correct. Some BIOS's list all virtual processors in >> the mptable (in which case the HTT patch is not needed and basically >> has no affect) but most only list the first core in each physical >> CPU. Enabling/disabling HT in the BIOS usually only affects ACPI's >> MADT table, not the MP table. The HT patch I wrote doesn't use the >> BIOS at all. It _only_ uses the values in registers returned from >> cpuid. > > I have personal experience with a machine that modifies the > contents of the MP Table, based on the BIOS settings, with > regard to hyperthreading. These are in the vast minority. > The problem with the use of the "cpuid 1" instruction to count > the number of cores on a processor is that doing this does not > take into account user settings in the BIOS, where hyperthreading > is intentionally being disabled, for whatever reason. Yes, which is why the real solution for 5.x going forward is to use ACPI's MADT. > One question this raises is whether or not ACPI would indicate > "present, but disabled" vs. "not present". The FALLBK approach > requires the former, if BIOS controls are to be maintained. This > is likely BIOS implementation dependent, unfortunately: if it's > even possible, some vendor likely implements their BIOS by making > the entries disappear from ACPI. ACPI enumerates present and disabled CPU's as present and disabled. The ACPI support is on my todo list, btw, but first I have to rework the APIC_IO support to work well with ACPI. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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