Date: Fri, 18 Sep 2009 18:48:07 +0300 From: Alexander Motin <mav@FreeBSD.org> To: "b. f." <bf1783@googlemail.com> Cc: jkim@FreeBSD.org, freebsd-acpi@FreeBSD.org, brueffer@FreeBSD.org, jhb@FreeBSD.org Subject: Re: acpi(4) corrections, clarifications Message-ID: <4AB3ABB7.30800@FreeBSD.org> In-Reply-To: <d873d5be0909180805h49c9a49ck7cd0177bcd04c1c@mail.gmail.com> References: <d873d5be0909180805h49c9a49ck7cd0177bcd04c1c@mail.gmail.com>
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b. f. wrote: > While this documentation cleanup is going on, I'd like to point out > that acpi(4) could use some improvements: > > (1)In the "SYSCTL VARIABLES" section, under hw.acpi.cpu.cx_lowest, > acpi(4) states "To enable ACPI CPU idling control, > machdep.cpu_idle_hlt must be set to 1". However, apparently only the > pc98 port still uses this OID, while amd64, i386, etc., use something > like machdep.idle=hlt, so this remark should be changed. And in any > case, is this statement correct? Can't idling now be used with other > values of machdep.idle, like mwait, mwait_hlt, amdc1e, hlt, and acpi? > > (2)Under the "BUGS" section, acpi(4) states: > > "The acpi CPU idle power management drive conflicts with the local > APIC (LAPIC) timer. Disable APIC mode with hint.apic.0.disabled or do > not use the C2 and C3 states if APIC mode is enabled." > > However, mav@, in his recent series of recommendations on > power-saving, advocated the use of hints like hint.apic.0.clock="0" > instead. Is simply turning off the timer sufficient to use the deeper > sleep states, or must all of the local apic be disabled? Some > machines won't boot with hint.apic.0.disabled, so it would be useful > to determine whether this is really necessary. It is enough to disable APIC timer to use C2/C3. No need to disable whole APIC. There were some objections that legacy timers may not route their interrupts properly on some new systems, but I am not sure whether disabling whole APIC help them somehow, but SMP it kill definitely. -- Alexander Motin
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