Date: Thu, 22 Mar 2012 23:43:18 -0700 From: Kevin Oberman <kob6558@gmail.com> To: perryh@pluto.rain.com Cc: mgamsjager@gmail.com, freebsd-stable@freebsd.org, john@theusgroup.com Subject: Re: powerd and increase in energy need Message-ID: <CAN6yY1uz5VDF-iD_26=gT-YZofc_CNc9qX6GaWv5pXuQK7RU0w@mail.gmail.com> In-Reply-To: <4f6b367c.iDW/lrO6B5MAYpoK%perryh@pluto.rain.com> References: <CA%2BD9Qhv5EmrkqvLetx9T5WD_1BRuCpUyZ=VYnRSjwRYqA7phdg@mail.gmail.com> <20120321000058.177F8256@server.theusgroup.com> <CA%2BD9QhsMMXYbLKg__jZx=7KbCHtK6LjqkfL9WSWs=pdT-t9r0w@mail.gmail.com> <CAN6yY1tKYbTjgQsL1gnfrc9r68c%2BQDCb1SAb%2BM=RFA90jvLpnw@mail.gmail.com> <4f6b367c.iDW/lrO6B5MAYpoK%perryh@pluto.rain.com>
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On Thu, Mar 22, 2012 at 7:26 AM, <perryh@pluto.rain.com> wrote: > Kevin Oberman <kob6558@gmail.com> wrote: > >> Throttling ... is intended for thermal control, not power >> management. The power savings will be negligible ... > > How can it possibly provide any thermal benefit, if it does not > reduce power consumption? =A0Is there some significant heat source, > other than power consumed, that throttling reduces? It does not provide reduced power because it was designed to control overheating. If hte CPU does not exceed the PSV temperature, it should not have any effect at all. That is its only purpose. If the system is idle, it makes no difference. If the CPU is loaded, it significantly lowers power consumption, but the operation takes longer to complete, so the total power consumed is often greater than it would have been with no throttling. Again, TCC is for thermal management, not power reduction. As to report I have seen that Cx states make things worse, I simply am baffled. I wonder if the power readings are really accurate. Theoretically the worst possible case is that there is no advantage to enabling Cx states. There should be no possible way to have it use more power. This is a real possibility, too, as it is very possible to have a system that simply would not use deeper sleep states. USB used to do exactly that, but it's been fixed with the new USB stack in 8. Other things like various forms of polling can also have this effect. You can check on whether your system is ever using deeper sleep by looking at dev.cpu.%d.cx_usage. Finally, all studies of power consumption agree that the lowest power usage is when CPU intensive code run as fast as possible when it is computing and then let deeper sleep modes sharply reduce power consumption when CPU is not needed. --=20 R. Kevin Oberman, Network Engineer E-mail: kob6558@gmail.com
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