Improvement of startup time
using Software Suspend
- Project Update Sony Corporation
Hiroki KAMINAGA
kaminaga@sm.sony.co.jp
2006/MAR/24
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Contents:
• aim
• swsusp functionality in detail
• use of swsusp for snapshot boot
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AIM:
• System startup time reduction
– By using image of known system state,
we try to accomplish kernel, module, and
application startup time reduction
• Other aspect
– By using system image as a file, we can trace
system development progress and error.
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Target envirionment:
• Target hardware
– OMAP OSK 5912 starter kit
•
Hardware Features:
ARM9 core operating at 192 Mhz.
DSP core operating at 192 Mhz.
Target software
TLV320AIC23 Stereo Codec
– Linux kernel 2.6.11
32 Mbyte DDR SDRAM
32 Mbyte Flash ROM
– Omap patch
RS-232 Serial Port
– U-boot
10 MBPS Ethernet port
USB Host Port
– Arm swsusp support patch
Compact flash connector
(developed and posted to ML)
On board IEEE 1149.1 JTAG
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Swsusp (1):
• 3 states supported by linux
– Standby state
• Minimal power savings, low latency to working
system. Cpu retains power. ACPI S1
– Suspend to ram
• Sufficient power savings, system in low-power.
Memory in self refresh mod. ACPI S3
– Suspend to disk
• Greatest power savings, similar to suspend to ram,
mem contents written to disk. ACPI S4
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Swsusp (2):
• Swsusp is suspend to disk
(or suspend to swap, `sw` stands for swap)
• Save image to nor flash instead of disk
• On resume, read from nor flash instead of
disk
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Swsusp (3):
• Basic flow of swsusp (suspend phase)
–
–
–
–
–
–
–
Freeze processes
Free unnecessary memory
Suspend devices
Make snapshot image (in memory)
Resume devices
Write snapshot image to swap
Powerdown machine
Note: swsusp needs half of total memory
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Swsusp (4):
• Basic flow of swsusp (resume)
–
–
–
–
–
–
–
Resume begin at `late_initcall`
Read image from swap to mem
Freeze process
Suspend devices
Restore snapshot image
Resume devices
Thaw processes
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Swsusp (5):
• Swsusp resume takes time.
– Swsusp procedure is kicked at late_initcall
• Almost before init process starts
– Doing I/O twice
• Swap to mem (allocated mem)
• Mem to mem (allocated mem to orig mem addr)
– Redundant device state transitions
• Device gets setup, suspend, and resume again.
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Snapshot boot (1):
• Co-operate kernel side suspend/resume
and boot loader side init setups
• Use snapshot image created by kernel
• Boot loader does:
–
–
–
–
Power up board
Load snapshot image to original memory
Initialize and do setups for resume
Jump to resume entry point
(not normal entry point)
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Snapshot boot (2):
restore resume
regs
dev
KERNEL
LAND
init
BOOT
LOADER board
copy
image
continue
process
setup
dev
ON
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Snapshot boot (3):
• Implemented in u-boot boot loader
– new command:
• bootss <image addr> <resume entry point>
– Procedure:
• Load snapshot image in flash to mem
• Initialization and setups
–
–
–
–
Setup clock speed
Setup timer
Setup various MMIO registers
Enable MMU
• Jump to resume entry point
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DEMO:
• [[[demo of swsusp and snapshot boot]]]
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Reference:
• Swsusp.txt
– Documentation/power/swsusp.txt
• Uboot
– http://sourceforge.net/projects/u-boot/
• Suspend2
– http://www.suspend2.net
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EOF
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