Fighting for the power.
Dmitry Kolosov
ivakras1 at gmail.com
Mon May 11 20:24:19 UTC 2009
Понедельник 11 мая 2009 23:13:09 Kevin Oberman писали:
> > From: Dmitry Kolosov <ivakras1 at gmail.com>
> > Date: Mon, 11 May 2009 22:59:13 +0400
> > Sender: owner-freebsd-acpi at freebsd.org
> >
> > Понедельник 04 мая 2009 02:18:14 Alexander Motin писали:
> > > I would like to summarize some of my knowledge on reducing FreeBSD power
> > > consumption and describe some new things I have recently implemented in
> > > 8-CURRENT. The main character of this story is my 12" Acer TravelMate
> > > 6292 laptop with C2D T7700 2.4GHz CPU, 965GM chipset and SATA HDD, under
> > > amd64 8-CURRENT.
> > >
> > > Modern systems, especially laptops, are implementing big number of
> > > power-saving technologies. Some of them are working automatically, other
> > > have significant requirements and need special system tuning or
> > > trade-offs to be effectively used.
> > >
> > > So here is the steps:
> > >
> > > 1. CPU
> > > CPU is the most consuming part of the system. Under the full load it
> > > alone may consume more then 40W of power, but for real laptop usage the
> > > most important is idle consumption.
> > > Core2Duo T7700 CPU has 2 cores, runs on 2.4GHz frequency, supports EIST
> > > technology with P-states at 2400, 2000, 1600, 1200 and 800MHz levels,
> > > supports C1, C2 and C3 idle C-states, plus throttling. So how can we use it:
> > > P-states and throttling
> > > Enabling powerd allows to effectively control CPU frequency/voltage
> > > depending on CPU load. powerd on recent system can handle it quite
> > > transparently. By default, frequency controlled via mix of EIST and
> > > throttling technologies. First one controls both core frequency and
> > > voltage, second - only core frequency. Both technologies give positive
> > > power-saving effect. But effect of throttling is small and can be
> > > completely hidden by using C2 state, that's why I recommend to disable
> > > throttling control by adding to /boot/loader.conf:
> > > hint.p4tcc.0.disabled=1
> > > hint.acpi_throttle.0.disabled=1
> > > In my case frequency/voltage control saves about 5W of idle power.
> > > C-states
> > > - C1 stops clock on some parts of CPU core during inactivity. It is
> > > safe, cheap and supported by CPUs for ages. System uses C1 state by default.
> > > - C2 state allows CPU to turn off all core clocks on idle. It is also
> > > cheap, but requires correct ACPI-chipset-CPU interoperation to be used.
> > > Use of C2 state can be enabled by adding to /etc/rc.conf:
> > > performance_cx_lowest="C2"
> > > economy_cx_lowest="C2"
> > > Effect from this state is not so big when powerd is used, but still
> > > noticeable,
> > > - C3 state allows CPU completely stop all internal clocks, reduce
> > > voltage and disconnect from system bus. This state gives additional
> > > power saving effect, but it is not cheap and require trade-offs.
> > > As soon as CPU is completely stopped in C3 state, local APIC timers in
> > > each CPU core, used by FreeBSD as event sources on SMP, are not
> > > functioning. It stops system time, breaks scheduling that makes system
> > > close to dead. The only solution for this problem is to use some
> > > external timers. Originally, before SMP era, FreeBSD used i8254 (for HZ)
> > > and RTC (for stats) chipset timers. I have made changes to 8-CURRENT to
> > > resurrect them for SMP systems. To use them, you can disable local APIC
> > > timers by adding to /boot/loader.conf:
> > > hint.apic.0.clock=0
> > > Also, to drop/rise voltage on C3, CPU needs time (57us for my system).
> > > It means that C3 state can't be effectively used when system is waking
> > > up often. To increase inactivity periods we should reduce interrupt rate
> > > as much as possible by adding to loader.conf:
> > > kern.hz=100
> > > It may increase system response time a bit, but it is not significant
> > > for laptop. Also we may avoid additional 128 interrupts per second per
> > > core, by the cost of scheduling precision, with using i8254 timer also
> > > for statistic collection purposes instead of RTC clock, by using another
> > > newly added option:
> > > hint.atrtc.0.clock=0
> > > As result, system has only 100 interrupts per core and CPUs are using C3
> > > with high efficiency:
> > > %sysctl dev.cpu |grep cx
> > > dev.cpu.0.cx_supported: C1/1 C2/1 C3/57
> > > dev.cpu.0.cx_lowest: C3
> > > dev.cpu.0.cx_usage: 0.00% 0.00% 100.00% last 7150us
> > > dev.cpu.1.cx_supported: C1/1 C2/1 C3/57
> > > dev.cpu.1.cx_lowest: C3
> > > dev.cpu.1.cx_usage: 0.00% 0.00% 100.00% last 2235us
> > > Result of effective C3 state usage, comparing to C2+powerd, is about 2W.
> > >
> > > 2. PCI devices
> > > PCI bus provides method to control device power. For example, I have
> > > completely no use for my FireWire controller and most of time - EHCI USB
> > > controller. Disabling them allows me to save about 3W of power. To
> > > disable all unneeded PCI devices you should build kernel without their
> > > drivers and add to loader.conf:
> > > hw.pci.do_power_nodriver=3
> > > To enable devices back all you need to do is just load their drivers as
> > > modules.
> > >
> > > 3. Radios
> > > WiFi and Bluetooth adapters can consume significant power when used (up
> > > to 2W when my iwn WiFi is connected) or just enabled (0.5W). Disabling
> > > them with mechanical switch on laptop case saves energy even when they
> > > are not connected.
> > >
> > > 4. HDA modem
> > > I was surprised, but integrated HDA modem consumed about 1W of power
> > > even when not used. I have used the most radical solution - removed it
> > > mechanically from socket. Case surface in that area become much cooler.
> > >
> > > 5. HDA sound
> > > To reduce number of sound generated interrupts I have added to the
> > > loader.conf:
> > > hint.pcm.0.buffersize=65536
> > > hint.pcm.1.buffersize=65536
> > > hw.snd.feeder_buffersize=65536
> > > hw.snd.latency=7
> > >
> > > 6. HDD
> > > First common recommendation is use tmpfs for temporary files. RAM is
> > > cheap, fast and anyway with you.
> > > Also you may try to setup automatic idle drive spin-down, but if it is
> > > the only system drive you should be careful, as every spin-up reduces
> > > drive's life time.
> > > For several months (until I have bought SATA SSD) I have successfully
> > > used SDHC card in built-in PCI sdhci card reader as main filesystem. On
> > > random read requests it is much faster then HDD, but it is very slow on
> > > random write. Same time it consumes almost nothing. USB drives could
> > > also be used, but effect is much less as EHCI USB controller consumes
> > > much power.
> > > Spinning-down my 2.5" Hitachi SATA HDD saves about 1W of power. Removing
> > > it completely saves 2W.
> > >
> > > 7. SATA
> > > Comparing to PATA, SATA interface uses differential signaling for data
> > > transfer. To work properly it has to transmit pseudo-random scrambled
> > > sequence even when idle. As you understand, that requires power. But
> > > SATA implements two power saving modes: PARTIAL and SLUMBER. These modes
> > > could be activated by either host or device if both sides support them.
> > > PARTIAL mode just stops scrambling, but keeps neutral link state, resume
> > > time is 50-100us. SLUMBER mode powers down interface completely, but
> > > respective resume time is 3-10ms.
> > > I have added minimal SATA power management to AHCI driver. There are
> > > hint.ata.X.pm_level loader tunables can be used to control it now.
> > > Setting it to 1 allows drive itself to initiate power saving, when it
> > > wish. Values 2 and 3 make AHCI controller to initiate PARTIAL and
> > > SLUMBER transitions after every command completion.
> > > Note that SATA power saving is not compatible with drive hot-swap, as
> > > controller unable to detect drive presence when link is powered-down.
> > > In my case PARTIAL mode saves 0.5W and SLUMBER - 0.8W of power.
> > >
> > > So what have I got? To monitor real system power consumption I am using
> > > information provided by ACPI battery via `acpiconf -i0` command:
> > >
> > > Original system:
> > > Design capacity: 4800 mAh
> > > Last full capacity: 4190 mAh
> > > Technology: secondary (rechargeable)
> > > Design voltage: 11100 mV
> > > Capacity (warn): 300 mAh
> > > Capacity (low): 167 mAh
> > > Low/warn granularity: 32 mAh
> > > Warn/full granularity: 32 mAh
> > > Model number: Victoria
> > > Serial number: 292
> > > Type: LION
> > > OEM info: SIMPLO
> > > State: discharging
> > > Remaining capacity: 93%
> > > Remaining time: 2:24
> > > Present rate: 1621 mA
> > > Voltage: 12033 mV
> > >
> > > Tuned system:
> > > %acpiconf -i0
> > > Design capacity: 4800 mAh
> > > Last full capacity: 4190 mAh
> > > Technology: secondary (rechargeable)
> > > Design voltage: 11100 mV
> > > Capacity (warn): 300 mAh
> > > Capacity (low): 167 mAh
> > > Low/warn granularity: 32 mAh
> > > Warn/full granularity: 32 mAh
> > > Model number: Victoria
> > > Serial number: 292
> > > Type: LION
> > > OEM info: SIMPLO
> > > State: discharging
> > > Remaining capacity: 94%
> > > Remaining time: 4:47
> > > Present rate: 826 mA
> > > Voltage: 12231 mV
> > >
> > > So I have really doubled my on-battery time by this tuning - 4:47 hours
> > > instead of 2:24 with default settings. Preinstalled vendor-tuned Windows
> > > XP on the same system, provides maximum 3:20 hours.
> > >
> >
> > My EC does not present rate and time info:
> > 10:49pm][/home/onyx# acpiconf -i0
> > Design capacity: 6000 mAh
> > Last full capacity: 3328 mAh
> > Technology: secondary (rechargeable)
> > Design voltage: 14800 mV
> > Capacity (warn): 172 mAh
> > Capacity (low): 104 mAh
> > Low/warn granularity: 10 mAh
> > Warn/full granularity: 25 mAh
> > Model number: Primary
> > Serial number:
> > Type: LION
> > OEM info: Hewlett-Packard
> > State: high
> > Remaining capacity: 100%
> > Remaining time: unknown
> > Present rate: unknown
> > Voltage: 12522 mV
> >
> > Where to dig? I'm realy need at least 'present rate' to fight for the
> > power.. Also it is an error in capacity detection, i think. Any ideas?
>
> Is the system connected to AC power when you issue the command? Many
> systems do not provide this information unless they are no battery
> power. Thy may also need to have been on battery for at least a minute
> or two to calculate drain rate. (Also, that battery is getting fairly
> old. It has only 55% of it's designed capacity.)
20 minutes on battery. Still no 'Remaining time' nor 'Present rate'. It drains 1% in a minute, while economy profile is C3 state for processor and 500MHz of speed. Anyway, laptop runs less than a hour on battery on economy profile. That laptop (HP Pavilion dv6840er) is less than 1 year old.
It's C4 state available in BIOS settings, i'll try it.
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