A Linux Power Management "mini-summit" was held on July 13th, 2009 - on the first day of the Montreal Linux Symposium. The Linux Symposium generously provided the facilities. We repeated the process used in 2008: http://lwn.net/Articles/292447/ This year the meeting room was more accessible to the general attendees of the Linux Symposium, so we had a fair number of "drop-ins". 25 signed in (listed below) plus a few more that came and went. While this exceeded our cap of 20, the extra people did not hinder our goal of focusing on a single discussion. Attendees --------- Len Brown - Intel - ACPI, SFI, Suspend co-Maintainer Howard Alyne - Wind River Pierre Phaneuf Rafael J. Wysocki - SUSE Labs/Novell, U. Warsaw; Hibernate and Suspend Maintainer Per-Inge Tallberg - Ericsson Rickard Andersson - Ericsson Paul Mundt - Renesas - SH Maintainer Magnus Damm - Renesas Richard Wooodruff - Texas Instruments, OMAP Stephen Hui - Zarlink John Linville - Red Hat - Wireless LAN maintainer Mark Brown - Marvell Samuel Thibault - labri.fr Lucas Nussbaun - inria.fr Srinivas Sripathi - Motorola Jason Baron - Red Hat Aristu Rozanaski - Red Hat - RHEL6 kernel maintainer Christopher Curtis - RipTide Software Klaus Pedersen - Nokia H. Peter Anvin - Intel - x86 maintainer Ernest Szedeman - Nortel Rick Leir - Leirtech David Ahern - Cisco Wending Wen - Rheinmetall Jason Chagas - Marvell Some of the attendees are in photos here: http://picasaweb.google.com/lenb417/2009LinuxSymposium# Agenda ------ 1. Review changes over the last year 2. Survey tools, techniques, workloads 3. Discuss upcoming work Summary of Power Management kernel changes since last year ---------------------------------------------------------- ACPI Platform BIOS compatibility fixes ACPI ACPI_SCI_EN work-around resume memory corruption workarounds hibernation: NVS memory handling handle overlapping memory zones suspend/resume framework re-work (Rafael Wysocki) shipped suspend/resume RTC test feature ordering update/workaround simplified driver interface now available r8169 etc. drivers now using it PCI PM framework re-worked to simplify drivers graphics drivers better support suspend/resume i915 video restore, though has bugs ATI making progress, especially older cards NVIDIA - continues to trail no open source support for devices after 7200 power aware scheduling sched_mc_power_savings per-CPU timers fixed clock_events_broadcast() bugs fixed (no longer needed on Westmere, which has always running LAPIC timer) range timers shipped upstream eg. range timers used android to group around wireless Intel shipped Nehalem (Core i7), which has always-running-TSC Run Time power management is receiving some attention now. OMAP (Richard Woodruff) 2008 had TI releasing aggressive full-off reference code on public portals Customers snapshotted this code at different points Heavy support burden ramping variants into production Linux-OMAP community have been creating a cleaner version of aggressive PM code suitable for mainline kernel in Linux-OMAP PM branch. Hope of reduced burden for future kernels with mainlined code ACPI sub-system (Len Brown) quality has been the focus for the last year. We continue to process about 300 bugs/year with 50-60 unresolved at any given time. Wireless: (John Linville) mac-80211 is now suspend/resume aware IEEE-80211 has run-time power saving features eg. negotiate w/ access point starting to deploy in drivers beacon filtering (reduces CPU wake-ups) TX power upcoming in cfg-80211 API Nokia tablets pushing power savings SH: (Paul Mundt) cpuidle integration using clocksources & clockevents from upstream can switch between timers depending on sleep states Hibernate & STR enabled, can test w/ RTC & kexec-jump-and-return s390: added suspend/resume support 5-second boot on Atom netbook for Moblin async API is upstream Fedora Core-11 boots in 20 seconds on a notebook Down from 60 seconds in Fedora Core-10 PM-QOS shipped Documentation/power/pm_qos_interface.txt Survey of Tools, Techniques, workloads for optimizing power management ---------------------------------------------------------------------- powertop bootchart bootgraph CONFIG_POWER_TRACER=y LTT-lite performance counters for energy coming OMAP uses on-board instrumentation suspend/resume debug I/F Power meters: O(100) Watts Up Pro; O(600) Extech; O(1000) Yokogawa O(600) HP/Agilent 34401A OMAP: measure per-power-plane w/ lab instruments 500mA vs uA range difficult to measure w/ precision multi-channel DAC - each channel calibrated to range Workloads for measuring power: handheld: no standard workloads however device vendors have internal benchmarks #1 idle #2 specific workloads #3 combination use-case SpecPower benchmark for servers (only) Energy Star for client computers idle only requires STR to be enabled by default Energy Star Server spec coming Future Energy Star wants to use energy benchmark BAPCO MobileMark 2007 for Windows Apple joined, so expect something new to work also on Apple No Linux Distro representation EEMBC released something or other... BLTK (Battery Life Toolkit) for Linux http://www.lesswatts.org/projects/bltk/ could use refresh could use handheld new workloads Future plans for the PM development, kernel side ------------------------------------------------- cpuidle C-states generalized to be platform idle states... platform driver can hide platform hooks into CPU power states Runtime PM for Platform Devices. 2.6.32 framework plan simmering SH running on top of prototype now context save/restore for power off power domain platform devices SH specific - Magnus IO devices eg PCI, USB - Alan Stern clock framework (started in ARM, now common on embedded) includes ref-counts/clock architecture specific implementation x86/ACPI system doesn't expose clock dependencies so unclear benefit to that arch Run-time PM of I/O devices, from the PCI POV mostly ability to put device into D1/D2 (~200us) /D3 (10ms) wakeup: PCIe #PME plug-event via root port (PCI #PME is less well specified) ACPI 4.0 adds D3hot Q: has an effect on _SD3? Hibernate/suspend: Axiom: we need more people fixing suspend/resume bugs Suspend2 aka "Tux on Ice" Spring 2009 patch set to replace hibernate w/ TOI was deemed impractical by upstream community, which prefers an incremental approach. Since, Nigel has sent specific patches to Rafael along the lines of gradual cherry-picking that upstream needs. First example is patch to compress hibernation image which Rafael thinks can be integrated. TOI is able to save larger hibernate images due to how it manages memory. This is a nice benefit and we'd like to see if we can do it upstream. patch review bandwidth limited 1. image compression 2. image saving performance currently very slow 3. ability to use multiple devices to save images including multiple swaps, and regular files 4. break the half-of-memory image limitation 5. Image encryption (solution for keys is an issue) It would be great to have Nigel supporting upstream hibernate. TOI supports snapshot boot via "kiosk mode" Hibernate & kexec kexec-jump is upstream (i386, SH, no x86_64) simplifies memory management of the "jumped to" code unclear if any other advantages. kexec-crash-dump is useful can make an oops "look less scary" and be automatic STR performance eliminate console switch async device resume android submitted "auto-suspend" patches compromise between low-level and high-level suspend invocation policy. cpuidle vs auto-suspend suspend is more "draconian", it stops timers etc for you. platform drivers in cpuidle can get to same place. Android OHA -Open Handset Alliance controls android license(s) Android = access to app-store Moblin shall support Android applications OMAP & SH specifics UIO - user space codec etc. have no concept of PM could use clock framework extension (clock framework is accessible via debugfs if necessary) interrupt coalescing deferred I/O to LCD delay until regular (infrequent) update interval use x-damage API to track change to visible screen SH running cpufreq on top of clock framework cpufreq has notifiers, clock framework does not lightweight CPU hotplug IBM proposed "idle throttling" approach using scheduler Intel is proposing simple "forced idle" RT thread PeterZ likes neither implementation, but favors the IBM approach in the long term. SH SMP wants to run Itron on some cores... low latency transition is important Memory Power Management Nokia project w/ U. in Brazil more pain than gain in memory offline prototype "partial RAM self refresh" page tables for kernel memory would allow moving kernel physical memory memory off-line incompatible with high-performance interleaving using NUMA node to segment memory allows tracking unused memory anti-fragmentation went upstream last year consensus: online/offline node granularity only ACPI 4.0 was published Error Reporting extensions processor aggregator device (forced idle to save power) D3hot generalized fan support thermal extensions IPMI op-region Len will do a Linux ACPI 4.0 presentation this Fall virtualization power management PM is still an after-though in the VMM space they have bigger problems KVM gets everything in Linux for free but could benefit from more info from the guests Xen gets to re-invent/port/re-implement everything in Linux VMMS have an easier time moving physical pages and thus doing memory power management -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
