# Power Management References - disk

[TOC]

## Hibernation Basics

Linux makes an image from current memory contents and system states using swap space. When user tries to resume, the make-shift image is loaded. As the system states are stored in persistence storage, memory can be powered off completely. This makes hibernation more power-saving than suspend-to-ram. On the other hand, resuming the system from contents in the disk may be slow. Thus resuming in general takes longer time.

## Setting up hibernation

Because of its nature, hibernation is much trickier to set up. For example, you'll need a swap partion or swap file for the hibernation image. See See [*Hibernation*](https://wiki.archlinux.org/title/Power_management/Suspend_and_hibernate#Hibernation) in *Power management/Suspend and hibernate* from Arch Linux wiki.

## Behaviors

The behavior of suspension can be obeserved in `dmesg` by runing `pm-hibernate` after enable the `/sys/power/pm_debug_messages`. The `pm-hibernate` is part of the `pm-utils` tool. You can install them on Ubuntu by:

$ sudo apt install pm-utils

To enable the `pm_debug_messages`, simply `cat` 1 into it:

$ sudo sh -c 'echo 1 > /sys/power/pm_debug_messages'

Doing this will enable extra messages regarding power management in the `dmesg`.

Finally, to start doing hibernation:

$ sudo pm-hibernate

Note that the machine hasn't setup swap files properly, so those are not catual hiberanation behaviors. That being said, some notable differences between suspend-to-ram can already be observed. For example, fomr logs you could see kernel trying to create image for hibernation.

### Suspension Behavior

[  486.343412] PM: hibernation: Configured hibernation resume from disk to 8388610
[  486.343416] PM: hibernation: Hibernation image partition 8:2 present
[  486.343416] PM: hibernation: Looking for hibernation image.
[  486.343419] PM: Image not found (code -16)
[  486.343420] PM: hibernation: Hibernation image not present or could not be loaded.
[  486.343434] PM: hibernation: Hibernation mode set to 'platform'
[  486.414408] PM: hibernation: hibernation entry
[  486.430803] Filesystems sync: 0.016 seconds
[  486.430808] Freezing user space processes ... (elapsed 0.002 seconds) done.
[  486.432950] OOM killer disabled.
[  486.433076] PM: hibernation: Marking nosave pages: [mem 0x00000000-0x00000fff]
[  486.433079] PM: hibernation: Marking nosave pages: [mem 0x00058000-0x00058fff]
[  486.433080] PM: hibernation: Marking nosave pages: [mem 0x000a0000-0x000fffff]
[  486.433083] PM: hibernation: Marking nosave pages: [mem 0x63355000-0x63355fff]
[  486.433085] PM: hibernation: Marking nosave pages: [mem 0x63355000-0x63355fff]
[  486.433086] PM: hibernation: Marking nosave pages: [mem 0x78d01000-0x78d48fff]
[  486.433088] PM: hibernation: Marking nosave pages: [mem 0x78d5d000-0x78d8efff]
[  486.433090] PM: hibernation: Marking nosave pages: [mem 0x78e39000-0x78e8efff]
[  486.433093] PM: hibernation: Marking nosave pages: [mem 0x78ed4000-0x78efefff]
[  486.433095] PM: hibernation: Marking nosave pages: [mem 0x78f85000-0x78fdefff]
[  486.433098] PM: hibernation: Marking nosave pages: [mem 0x79000000-0xffffffff]
[  486.435101] PM: hibernation: Basic memory bitmaps created
[  486.435164] PM: hibernation: Preallocating image memory
[  487.293741] PM: hibernation: Allocated 1489814 pages for snapshot
[  487.293745] PM: hibernation: Allocated 5959256 kbytes in 0.85 seconds (7010.88 MB/s)
[  487.293747] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
[  487.295314] printk: Suspending console(s) (use no_console_suspend to debug)
[  487.446347] PM: freeze of devices complete after 151.027 msecs
[  487.472987] PM: late freeze of devices complete after 26.634 msecs
[  487.473373] ACPI: EC: interrupt blocked
[  487.474286] PM: noirq freeze of devices complete after 1.263 msecs
[  487.474289] PM: end freeze of devices complete after 27.936 msecs
[  487.474290] ACPI: PM: Preparing to enter system sleep state S4
[  487.474865] ACPI: EC: event blocked
[  487.474866] ACPI: EC: EC stopped
[  487.474866] ACPI: PM: Saving platform NVS memory
[  487.475044] Disabling non-boot CPUs ...
[  487.476593] smpboot: CPU 1 is now offline
[  487.487157] smpboot: CPU 2 is now offline
[  487.489168] smpboot: CPU 3 is now offline
[  487.494976] smpboot: CPU 4 is now offline
[  487.500770] smpboot: CPU 5 is now offline
[  487.502399] smpboot: CPU 6 is now offline
[  487.504000] smpboot: CPU 7 is now offline
[  487.504306] Checking wakeup interrupts
[  487.504308] Calling kvm_suspend+0x0/0x30 [kvm]
[  487.504347] Calling mce_syscore_suspend+0x0/0x20
[  487.504350] Calling ledtrig_cpu_syscore_suspend+0x0/0x20
[  487.504353] Calling timekeeping_suspend+0x0/0x2e0
[  487.504384] Calling irq_gc_suspend+0x0/0x80
[  487.504387] Calling save_ioapic_entries+0x0/0x170
[  487.504455] Calling i8259A_suspend+0x0/0x40
[  487.504459] Calling fw_suspend+0x0/0x20
[  487.504461] Calling acpi_save_bm_rld+0x0/0x30
[  487.504471] Calling intel_epb_save+0x0/0x40
[  487.504473] Calling lapic_suspend+0x0/0x30
[  487.504483] PM: hibernation: Creating image:
[  487.738865] PM: hibernation: Need to copy 1462837 pages
[  487.738867] PM: hibernation: Normal pages needed: 1462837 + 1024, available pages: 2699502
[  489.139089] PM: hibernation: Image created (1462837 pages copied)

### Resuming Behavior

[  487.504861] ACPI: PM: Restoring platform NVS memory
[  487.504899] ACPI: EC: EC started
[  487.504900] Calling init_counter_refs+0x0/0x60
[  487.504905] Calling lapic_resume+0x0/0x30
[  487.504927] Calling intel_epb_restore+0x0/0x90
[  487.504928] Calling acpi_restore_bm_rld+0x0/0x70
[  487.504934] Calling irqrouter_resume+0x0/0x60
[  487.504937] Calling i8259A_resume+0x0/0x40
[  487.505081] Calling i8237A_resume+0x0/0xd0
[  487.505143] Calling ioapic_resume+0x0/0x150
[  487.505166] Calling irq_gc_resume+0x0/0x80
[  487.505169] Calling irq_pm_syscore_resume+0x0/0x20
[  487.505177] Calling timekeeping_resume+0x0/0x170
[  487.505210] Timekeeping suspended for 0.951 seconds
[  487.505220] Calling ledtrig_cpu_syscore_resume+0x0/0x20
[  487.505224] Calling mce_syscore_resume+0x0/0x30
[  487.505237] Calling microcode_bsp_resume+0x0/0x70
[  487.505240] Calling kvm_resume+0x0/0x30 [kvm]
[  487.505279] Enabling non-boot CPUs ...
[  487.505331] x86: Booting SMP configuration:
[  487.505332] smpboot: Booting Node 0 Processor 1 APIC 0x2
[  487.511635] CPU1 is up
[  487.511672] smpboot: Booting Node 0 Processor 2 APIC 0x4
[  487.516582] CPU2 is up
[  487.516612] smpboot: Booting Node 0 Processor 3 APIC 0x6
[  487.521457] CPU3 is up
[  487.521487] smpboot: Booting Node 0 Processor 4 APIC 0x1
[  487.526552] CPU4 is up
[  487.526580] smpboot: Booting Node 0 Processor 5 APIC 0x3
[  487.531500] CPU5 is up
[  487.531531] smpboot: Booting Node 0 Processor 6 APIC 0x5
[  487.536754] CPU6 is up
[  487.536782] smpboot: Booting Node 0 Processor 7 APIC 0x7
[  487.541815] CPU7 is up
[  487.545327] ACPI: PM: Waking up from system sleep state S4
[  487.547392] ACPI: EC: interrupt unblocked
[  487.566645] PM: noirq thaw of devices complete after 19.437 msecs
[  487.567123] PM: early thaw of devices complete after 0.417 msecs
[  487.567236] ACPI: EC: event unblocked
[  487.894462] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[  487.895574] ata1.00: unexpected _GTF length (8)
[  487.896233] ata1.00: unexpected _GTF length (8)
[  487.896389] ata1.00: configured for UDMA/133
[  491.095942] PM: thaw of devices complete after 3528.747 msecs
[  491.096252] PM: hibernation: Writing hibernation image.
[  491.097584] PM: Using 3 thread(s) for compression
[  491.097586] PM: Compressing and saving image data (1465695 pages)...
[  491.097593] PM: Image saving progress:   0%
[  491.674061] PM: Image saving progress:  10%
[  492.233351] PM: Image saving progress:  20%
[  493.631248] PM: Image saving progress:  30%
[  495.120169] PM: Image saving progress:  40%
[  496.439402] PM: Image saving progress:  50%
[  498.121164] PM: Image saving progress:  60%
[  499.713156] PM: Image saving progress:  70%
[  501.333536] PM: Image saving progress:  80%
[  501.676735] PM: hibernation: Wrote 5862780 kbytes in 10.57 seconds (554.66 MB/s)
[  501.878115] PM: hibernation: Basic memory bitmaps freed
[  501.878120] OOM killer enabled.
[  501.878121] Restarting tasks ... 
[  501.878210] usb 2-4: USB disconnect, device number 2
[  501.881219] done.
[  501.947069] video LNXVIDEO:00: Restoring backlight state
[  501.947267] PM: hibernation: hibernation exit