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Date:      Thu, 22 Mar 2012 14:59:46 +0100
From:      Luigi Rizzo <rizzo@iet.unipi.it>
To:        Alexander Leidinger <Alexander@leidinger.net>
Cc:        Matthias Gamsjager <mgamsjager@gmail.com>, freebsd-stable@freebsd.org, John <john@theusgroup.com>
Subject:   Re: powerd and increase in energy need
Message-ID:  <CA%2BhQ2%2BgP3K3xLzhxCoDCZCYL%2BjW5Q4cTT5a5F4GkifmzOsiBKA@mail.gmail.com>
In-Reply-To: <20120322105109.Horde.srohf5jmRSRPavYNP_frKBA@webmail.leidinger.net>
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> <20120321173728.GA41322@onelab2.iet.unipi.it> <20120322105109.Horde.srohf5jmRSRPavYNP_frKBA@webmail.leidinger.net>

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On Thu, Mar 22, 2012 at 10:51 AM, Alexander Leidinger <
Alexander@leidinger.net> wrote:

> Quoting Luigi Rizzo <rizzo@iet.unipi.it> (from Wed, 21 Mar 2012 18:37:28
> +0100):
>
>  I guess that the credit for power saving goes mostly to the CPU
>> architects. Powerd only gives second-order savings, and C1 vs. C3
>> is ineffective, at least for HZ=1000
>>
>>        CPU     Power (watts)
>>        freq    idle    16 threads
>>        -----------------------
>>         200     48      51
>>        2200     52      83
>>        3200     54     115
>>        3401     56     118
>>
>>        powerd   48     118
>>
>
> I hope you all don't use a cheap PSU, but a _good_ high efficient one,
> which really draws less power when idle instead of generating heat. Some
> PSUs are only efficient in a sweet spot, instead of being efficient over a
> broad range, even when being idle. See http://en.wikipedia.org/wiki/**
> 80_PLUS <http://en.wikipedia.org/wiki/80_PLUS>; for a quick and not so
> in-deep overview (and the reality may differ from manufacturer to
> manufacturer).
>

it isn't such a big deal in my opinion. The %efficiency at low
levels is misleading if you don't factor out the 5-10W plateau for keeping
the
PSU alive (fan, ballast, etc.). See for instance

http://www.techpowerup.com/reviews/Antec/HCG-520/5.html

the table at the end of the page reports 6.73W of idle power. At 40W
this PSU consumes 52.9W, so the apparent efficiency is 75%, but
factoring out the idle power you go way up.

cheers
luigi

-- 
> That does not compute.
>
> http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
> http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137
>
>


-- 
-----------------------------------------+-------------------------------
 Prof. Luigi RIZZO, rizzo@iet.unipi.it  . Dip. di Ing. dell'Informazione
 http://www.iet.unipi.it/~luigi/        . Universita` di Pisa
 TEL      +39-050-2211611               . via Diotisalvi 2
 Mobile   +39-338-6809875               . 56122 PISA (Italy)
-----------------------------------------+-------------------------------



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