Date: Thu, 24 Feb 2005 18:08:43 -0500 From: Chuck Swiger <cswiger@mac.com> To: Maxim Sobolev <sobomax@portaone.com> Cc: current@FreeBSD.ORG Subject: Re: patch: p4tcc and speedstep cpufreq drivers Message-ID: <421E5E7B.5040104@mac.com> In-Reply-To: <421E49D9.60803@portaone.com> References: <20050224011924.992A65D07@ptavv.es.net> <421DA0B5.4060705@portaone.com> <421E42F2.6010105@root.org> <421E49D9.60803@portaone.com>
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Maxim Sobolev wrote: > Nate Lawson wrote: [ ... ] >> "On-Demand mode may be used at the same time Automatic mode is >> enabled, however, if the system (tries to enable the TCC via On-Demand >> mode[1]) at the same time (automatic mode is enabled[2]) AND (a high temperature >> condition exists [3]), the duty cycle of the automatic mode will override >> the duty cycle selected by the On-Demand mode." >> >> Since automatic mode is set by the BIOS before we even boot, things >> should be fine. > > Well, this is quite tricky part of the spec. My reading is that the > paragraph above applies only to situation if you are (trying to set > on-demand mode [1]) when both (automatic mode is in effect [2]) *and* (high > temperature condition already exists [3]), in that case automatic mode will > win and override any manual settings. I suspect you'd read your paragraph with [1] and [2] joined together, but they can be read seperately just as the spec can. :-) > However, in the case when you have on-demand mode already on and high > temperature condition emerges it will have no effect on duty cycle until > THERMTRIP# kicks in. > > That's in my view explains why there is big AND in the text above. I think the spec is advising developers who try to control TCC that if PROCHOT gets asserted, the CPU may override the programmed settings in favor of the automatic ones. I don't think the spec is asserting that the CPU is forbidden from reducing power usage if PROCHOT condition is detected, regardless of what automatic mode is set to. A reasonable processor would drop to a known minimal power usage state-- hopefully one low enough to keep the CPU from completely overheating even if a fan has failed-- if PROCHOT is seen. [ It may also be the case that a CPU does not do so, in which case the ACPI driver code ought to try to pay attention to PROCHOT and reduce power consumption regardless and not just depend on CPU failsafes to work. If that is your position, well, I would agree with this. :-) ] -- -Chuck
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