Improving Xen idle power efficiency

Xen Power ImprovementsWill Auld, Yang Z Zhang, Winston WangIntel Corporation

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Agenda• Background• Power saving in client• Power saving in server• Summary 3

Room to save POWER• Ideal/standard  Native OS power consumption• Reality  Hypervisor power consumption• LARGE DELTA (~40% for client at start) 4

Client architecture Client Xen Configuration Linux Win7 DomU Dom0 DomU VM VM VM Xen Hypervisor Hardware 5

Goal • Native OS power efficiency • Close the Power gap with Native Win7 Code Drop Fix Identify Code Gap Root Cause 6

Current results• ~40% idle power gap 2 years ago• ~5% idle power gap now Idle Power Gap 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Project Start Project End• More?• Increasingly harder to extract 7

LCD brightness control LCD Display – ~20% idle power − Broken brightness controls Win7> Dom0> Fix: −Added emulation of ACPI video extension − Specifically, brightness control methods _BCL, _BCM, and _BQC − Added to VM guest ACPI BIOS − Pass through control knob output to Dom0 take platform action −Make sure Dom0 LCD brightness is really working 8

Runtime IO power managementDysfunctional IO power management• ~15% Idle power• 1st available in 2.6.32 kernel, but: − not functioning correctlyFix:• Enable energy-saving states at run time and auto suspended when idle• Gap dropped from ~25% to 6.8% after fix − HP 8440p mobile platform based on Nehalem processor 9

ATA_link power Max_PerfATA_link static power setting− ~6% idle power in max_performance Run Time− But performance suffers with min_power− Even worse: −All SCSI hosts active with/without attached devices Mim_PowerFix:− Runtime update for ATA_link power setting −Toggle min_power / max_performance, as needed− Disable clocks on deviceless ports 10

Network powerWired and Wi-Fi− ~16 % idle power (650mw)− Many interrupts break deep c state during idle Win7> Dom0>Fix:− Enable Wi-Fi and E1000 power saving mode in Dom0− Add Win7 power management PV driver to pass control settings to Dom0 11

GFX power managementiGFX power management inactive− ~16% idle power (650mw)− VT-d requires device reset −Reset clears all regs including BIOS enabled power management regs − Disables: RC6 (render standby), turbo, and GPMT (Graphics Power Modulation Technology) VT-d operation BIOS PM ON PM PM ON Reset OFF Save / RestoreFix:− Save/Restore PM registers around FLR 12

Client summary• Started with a ~40% gap• Ended with ~5% gap• Greatly improved and got close to the goal 13

Server power savings -- increasing idle time• Timer alignment• Power aware scheduling• Reducing periodic tasks 14

Timer alignment• Independent, frequent timer interrupts • Frequent wake-ups• Reduced idle time, greater power consumption intr arrived intr arrived Timer intr idle busy idle busy Cpu0: CPU idle CPU busy intr arrived Cpu1: Resultant Socket Socket C-state : 15

Timer alignment• Proposal • Configurable timer consolidate window, such as 50 ns • Compute timer interrupt moment • Shift timer handle moment to next timer consolidate moment• Benefit • Fewer interrupts  longer idle time  power savings• Challenges • Guest schedule impact– performance impact • Cross CPU timer synchronization • IPI frequency and synchronization 16

Timer alignment intr arrived intr arrived Timer intr idle busy idle busy Cpu0: CPU idle CPU busy New intr arrived intr arrived Cpu1: Resultant Socket Socket C-state : Gained C-State• Shifting CPU1’s interrupt to match CPU0’s Nice gain in C-State• Repeated over and over adds up 17

Power aware scheduling• ACPI modes – − Performance  Power hungry mode − Energy mode  Power savings mode − Balanced• Task to Scheduling − Performance − Schedule vCPUs one per physical core before pairing − Energy − Schedule vCPUs one per logical core  − power down more cores  − power down more sockets 18

Power saving scheduler packages pkg 0 pkg 1 cores core 0 core 1 core 0 core 1 HT cpu 0 cpu 1 cpu 2 cpu 3 cpu 4 cpu 5 cpu 6 cpu 7running task vcpu0 vcpu1 vcpu2 power aware scheduler Idle CPU/in deep C-state Busy CPU Not in deep C-state 19

Reduce periodic activity• Power-unfriendly RTC emulation: − VMM updates RTC clock twice per second − Solution − Update RTC clock only on Read If a clock ticks where no one can see it, does the time change?• Frequent Wake-ups to check buffered I/O: − Wakeup multiple times a second (Polling model) − Solution (Push model) − Event channel to notify buffered I/O change status No more polling 20

Server summary• Significant areas of work• Need to quantify the impacts 21

Overall summary• Every component counts – software and hardware• Make sure the basics are working• Still more to do 22

Questions? 23

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Improving Xen idle power efficiency

by XenProject.org on Sep 04, 2012

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