Fighting for the power.

[Dmitry Kolosov]

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?