1. Improvement of startup time using Software Suspend - Project Update -
Sony Corporation
Hiroki KAMINAGA
2006/MAR/24
JapanTechnicalJamboree7

2. JapanTechnicalJamboree7
Contents:
aim
swsusp functionality in detail
use of swsusp for snapshot boot
2006/MAR/24
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3. JapanTechnicalJamboree7
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.
2006/MAR/24
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Target envirionment:
Target hardware
OMAP OSK 5912 starter kit
Target software
Linux kernel
Omap patch
U-boot
Arm swsusp support patch (developed and posted to ML)
Hardware Features:
ARM9 core operating at 192 Mhz.
DSP core operating at 192 Mhz.
TLV320AIC23 Stereo Codec
32 Mbyte DDR SDRAM
32 Mbyte Flash ROM
RS-232 Serial Port
10 MBPS Ethernet port
USB Host Port
Compact flash connector
On board IEEE JTAG
2006/MAR/24
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5. JapanTechnicalJamboree7
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
2006/MAR/24
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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
2006/MAR/24
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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
Power off device, save (co)processor regs, snapshot, restore regs, poweron device, write to swap
Note: swsusp needs half of total memory
2006/MAR/24
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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
Check sig, alloc mem, read image, freeze process, free mem, suspend dev, poweroff dev,
Save processor regs, realloc image to orig addr, restore regs, poweron dev, resume dev, free mem thaw process
2006/MAR/24
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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.
2006/MAR/24
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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)
2006/MAR/24
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11. JapanTechnicalJamboree7
Snapshot boot (2):
restore
regs
resume
dev
continue
process
KERNEL
LAND
init
board
copy
image
setup
dev
BOOT
LOADER ON
2006/MAR/24
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12. JapanTechnicalJamboree7
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
2006/MAR/24
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DEMO:
[[[demo of swsusp and snapshot boot]]]
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14. JapanTechnicalJamboree7
Reference:
Swsusp.txt
Documentation/power/swsusp.txt
Uboot
Suspend2
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EOF
2006/MAR/24
JapanTechnicalJamboree7