236 lines
8.2 KiB
Plaintext
236 lines
8.2 KiB
Plaintext
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From kernel/suspend.c:
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* BIG FAT WARNING *********************************************************
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*
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* If you have unsupported (*) devices using DMA...
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* ...say goodbye to your data.
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*
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* If you touch anything on disk between suspend and resume...
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* ...kiss your data goodbye.
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*
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* If your disk driver does not support suspend... (IDE does)
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* ...you'd better find out how to get along
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* without your data.
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*
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* If you change kernel command line between suspend and resume...
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* ...prepare for nasty fsck or worse.
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*
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* If you change your hardware while system is suspended...
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* ...well, it was not good idea.
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*
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* (*) suspend/resume support is needed to make it safe.
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You need to append resume=/dev/your_swap_partition to kernel command
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line. Then you suspend by
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echo shutdown > /sys/power/disk; echo disk > /sys/power/state
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. If you feel ACPI works pretty well on your system, you might try
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echo platform > /sys/power/disk; echo disk > /sys/power/state
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Article about goals and implementation of Software Suspend for Linux
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Author: G<><47>bor Kuti
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Last revised: 2003-10-20 by Pavel Machek
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Idea and goals to achieve
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Nowadays it is common in several laptops that they have a suspend button. It
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saves the state of the machine to a filesystem or to a partition and switches
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to standby mode. Later resuming the machine the saved state is loaded back to
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ram and the machine can continue its work. It has two real benefits. First we
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save ourselves the time machine goes down and later boots up, energy costs
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are real high when running from batteries. The other gain is that we don't have to
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interrupt our programs so processes that are calculating something for a long
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time shouldn't need to be written interruptible.
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swsusp saves the state of the machine into active swaps and then reboots or
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powerdowns. You must explicitly specify the swap partition to resume from with
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``resume='' kernel option. If signature is found it loads and restores saved
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state. If the option ``noresume'' is specified as a boot parameter, it skips
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the resuming.
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In the meantime while the system is suspended you should not add/remove any
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of the hardware, write to the filesystems, etc.
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Sleep states summary
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====================
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There are three different interfaces you can use, /proc/acpi should
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work like this:
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In a really perfect world:
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echo 1 > /proc/acpi/sleep # for standby
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echo 2 > /proc/acpi/sleep # for suspend to ram
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echo 3 > /proc/acpi/sleep # for suspend to ram, but with more power conservative
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echo 4 > /proc/acpi/sleep # for suspend to disk
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echo 5 > /proc/acpi/sleep # for shutdown unfriendly the system
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and perhaps
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echo 4b > /proc/acpi/sleep # for suspend to disk via s4bios
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Frequently Asked Questions
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==========================
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Q: well, suspending a server is IMHO a really stupid thing,
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but... (Diego Zuccato):
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A: You bought new UPS for your server. How do you install it without
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bringing machine down? Suspend to disk, rearrange power cables,
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resume.
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You have your server on UPS. Power died, and UPS is indicating 30
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seconds to failure. What do you do? Suspend to disk.
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Ethernet card in your server died. You want to replace it. Your
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server is not hotplug capable. What do you do? Suspend to disk,
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replace ethernet card, resume. If you are fast your users will not
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even see broken connections.
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Q: Maybe I'm missing something, but why don't the regular I/O paths work?
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A: We do use the regular I/O paths. However we cannot restore the data
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to its original location as we load it. That would create an
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inconsistent kernel state which would certainly result in an oops.
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Instead, we load the image into unused memory and then atomically copy
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it back to it original location. This implies, of course, a maximum
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image size of half the amount of memory.
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There are two solutions to this:
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* require half of memory to be free during suspend. That way you can
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read "new" data onto free spots, then cli and copy
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* assume we had special "polling" ide driver that only uses memory
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between 0-640KB. That way, I'd have to make sure that 0-640KB is free
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during suspending, but otherwise it would work...
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suspend2 shares this fundamental limitation, but does not include user
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data and disk caches into "used memory" by saving them in
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advance. That means that the limitation goes away in practice.
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Q: Does linux support ACPI S4?
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A: Yes. That's what echo platform > /sys/power/disk does.
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Q: My machine doesn't work with ACPI. How can I use swsusp than ?
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A: Do a reboot() syscall with right parameters. Warning: glibc gets in
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its way, so check with strace:
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reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 0xd000fce2)
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(Thanks to Peter Osterlund:)
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#include <unistd.h>
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#include <syscall.h>
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#define LINUX_REBOOT_MAGIC1 0xfee1dead
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#define LINUX_REBOOT_MAGIC2 672274793
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#define LINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2
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int main()
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{
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syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
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LINUX_REBOOT_CMD_SW_SUSPEND, 0);
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return 0;
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}
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Also /sys/ interface should be still present.
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Q: What is 'suspend2'?
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A: suspend2 is 'Software Suspend 2', a forked implementation of
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suspend-to-disk which is available as separate patches for 2.4 and 2.6
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kernels from swsusp.sourceforge.net. It includes support for SMP, 4GB
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highmem and preemption. It also has a extensible architecture that
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allows for arbitrary transformations on the image (compression,
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encryption) and arbitrary backends for writing the image (eg to swap
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or an NFS share[Work In Progress]). Questions regarding suspend2
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should be sent to the mailing list available through the suspend2
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website, and not to the Linux Kernel Mailing List. We are working
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toward merging suspend2 into the mainline kernel.
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Q: A kernel thread must voluntarily freeze itself (call 'refrigerator').
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I found some kernel threads that don't do it, and they don't freeze
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so the system can't sleep. Is this a known behavior?
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A: All such kernel threads need to be fixed, one by one. Select the
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place where the thread is safe to be frozen (no kernel semaphores
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should be held at that point and it must be safe to sleep there), and
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add:
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if (current->flags & PF_FREEZE)
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refrigerator(PF_FREEZE);
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If the thread is needed for writing the image to storage, you should
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instead set the PF_NOFREEZE process flag when creating the thread.
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Q: What is the difference between between "platform", "shutdown" and
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"firmware" in /sys/power/disk?
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A:
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shutdown: save state in linux, then tell bios to powerdown
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platform: save state in linux, then tell bios to powerdown and blink
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"suspended led"
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firmware: tell bios to save state itself [needs BIOS-specific suspend
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partition, and has very little to do with swsusp]
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"platform" is actually right thing to do, but "shutdown" is most
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reliable.
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Q: I do not understand why you have such strong objections to idea of
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selective suspend.
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A: Do selective suspend during runtime power managment, that's okay. But
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its useless for suspend-to-disk. (And I do not see how you could use
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it for suspend-to-ram, I hope you do not want that).
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Lets see, so you suggest to
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* SUSPEND all but swap device and parents
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* Snapshot
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* Write image to disk
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* SUSPEND swap device and parents
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* Powerdown
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Oh no, that does not work, if swap device or its parents uses DMA,
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you've corrupted data. You'd have to do
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* SUSPEND all but swap device and parents
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* FREEZE swap device and parents
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* Snapshot
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* UNFREEZE swap device and parents
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* Write
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* SUSPEND swap device and parents
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Which means that you still need that FREEZE state, and you get more
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complicated code. (And I have not yet introduce details like system
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devices).
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Q: There don't seem to be any generally useful behavioral
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distinctions between SUSPEND and FREEZE.
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A: Doing SUSPEND when you are asked to do FREEZE is always correct,
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but it may be unneccessarily slow. If you want USB to stay simple,
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slowness may not matter to you. It can always be fixed later.
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For devices like disk it does matter, you do not want to spindown for
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FREEZE.
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Q: After resuming, system is paging heavilly, leading to very bad interactivity.
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A: Try running
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cat `cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u` > /dev/null
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after resume. swapoff -a; swapon -a may also be usefull.
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