Do ACPI (S3 S4) and resume it.

Do S3 S4 and resume it.

e.g.:...-global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0

I. How to do S3 
Linux guest:
# pm-suspend
Windows guest :
Preparation: For do S3,install qxl driver:
Control panel--->Device manager--->Display Adapters-->update
a.win7,winXP,win2003: Click Start-->Turn Off computer-->choose Sleep
b.win2012 win8 win2008:Control panel-->Power Options-->Change what the power buttons do-->Power button settins-->select "Sleep"-->save changes
(qemu)system_powerdown
II. How to do S4
Linux guest:
# pm-hibernate
Windows guest:
a.win7,winXP,win2003: Click Start-->Turn Off computer-->choose hibernate
b.win2012 win8 win2008:Control panel-->Power Options-->Change what the power buttons do-->Power button settins-->select "hibernate"-->save changes
(qemu)system_powerdown

I.For S3 resume:
(1) Press the keyboard.
(2) Send "system_wakeup" qemu command.
(3) Click the mouse in the guest. (Need to use the PS/2 mouse, USB mouse is not supported.)
(4) RTC to wakeup guest:
For linux guest: For example:  #rtcwake  -m mem -t 20s  (Guest will wakeup automatically after 20s)
For windows guest:   "start" -> "control-panel" -> "System and Security" -> "Administrative Tools"-> "Task Scheduler". Select "Create Task..." and create a task as following:
   in the "General" tab, fill in "Name" and "Description", check "Run with highest privileges".
   in the "Action" tab, new a action with "Display a message"
   in the "Conditions" tab check "Wake the computer to run this task".
   in the "Triggers" tab, new a trigger, set one time and select "enabled".
II.For S4 resume:
Boot guest with same CLI.