Transcript uClinux vs Linux Context Switching and IPC Performance

uClinux vs Linux
Context Switching and IPC
Performance Comparison
2004.09.10
Heechul Yun
Digital Media R&D Center
Contents
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Introduction
ARM9 Cache Architecture
Benchmark
IPC Performance
Context Switching Performance
Conclusion
Future Works
Introduction
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Objective
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Context switch
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Fair performance comparison of uClinux and Linux
Focused on Context Switching and IPC
Restore register and address space of next process
IPC (Inter Process Communication)
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Send & recv messages between processes
uClinux vs Linux
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Linux
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Separate virtual address space for each process
Need to recover address space on context
switching
uClinux
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Single shared address space for all process
No need to recover address space on context
switching
uClinux may be better on context switching
ARM9 MMU Architecture
VA
PA
TLB
Perm
I-Cache
CPU
Memory
D-Cache
Data
Virtually-indexed caches:
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Flush cache on context switch
Direct cost : 1k~18k cycles
Indirect cost : up to 54k cycles
 Up to 270us on 200MHz
Observation:
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Can avoid cache flush if no
address overlap
ARM926EJ-S Virtual Cache Architecture
32
12 11
Tag
Index
1
2
3
4
.
.
.
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128
TAG
=
Hit
5 4
2 1 0
Word Byte
1 2 3 2
4. 5 6 7 8
=
Read data
• Fully virtual address based index & tag
• Separate 4way set-associative 16K I&D Cache.
• 8word for each cache line
Benchmark
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Lmbench2 [Lmbench]
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Famous OS benchmark
Modified for uClinux (vfork, FIFO)
lat_ctx, lat_fifo, bw_pipe is used..
Master
read
write
FIFO 0
Child1
read
write
Child2
read
write
FIFO 1
‘lat_ctx’ FIFO architecture
FIFO 2
Benchmark Setup
App
Kernel
H/W
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LMBench2
lat_fifo, lat_ctx, bw_pipe used
Linux-2.6.7
uClinux 2.6.7
H/W: SMDK24A0
- ARM926ejs based S3C24A0
- 16K I&D Cache
Same H/W, Same Benchmark program are used
The only difference is kernel (uClinux, Linux)
Context Switching Performance
0KB workload
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Each proc immediately
switch to next
pure ctx overhead
comparison
120
100
Context switch time[us]
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80
60
40
20
0
2
4
6
8
10
12
Processes
uclinux
linux
14
16
IPC Performance
Linux
uClinux
Ratio
Lat_fifo
(us)
160.64
31.74
5.06
Bw_pipe
(MB/s)
12.58
25.55
2.03
Conclusion
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The first fair performance comparison between
uClinux and Linux
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Same H/W platform
Same benchmark S/W
uClinux has better IPC & Context switching
performance
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Because cache is valid on context switching
Beneficial for
 Real-time critical application
 IPC oriented application
Future Work (?)
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Extending benchmarks
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Interrupt latency, ….
Share the result with community
Improving uClinux
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Need protection
 inherit ‘Single Address Space Operating System’
research for 64bit processors
More compatibility
 No fork()
 Fixed heap & stack size
Reference
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[FASS’03] Adam Wiggins et el. “Implementations of Fast
Address-Space Switching and TLB Sharing on the StrongARM
Processor”, in the Proceddings of the 8th Australia-Pacific
Computer Systems Architecture Conference, Aizu-Wakmatsu
City, Japan, September 2003.
[LmBench’96] McVoy, L., Staelin, C. “lmbench: Portable tools
for performance analysis”. In: Proceedings of the 1996
[UC] uClinux/ARM 2.6 Project.
http://opensrc.sec.samsung.com/
USENIX Technical Conference, San Diego, CA, USA (2996)
[24A0] Samsung S3C24A0 Product Datasheet.
http://www.samsung.com/Products/Semiconductor/SystemLSI
/MobileSolutions/MobileASSP/MobileComputing/S3C24A0/S3C
24A0.htm
[926] ARM926EJ-S Technical Reference Manual.
http://www.arm.com/pdfs/DDI0198D_926_TRM.pdf
[ARM] ARM Architecture Reference Manual. ARM LTD.
보조 TP
Context Switching Performance
400
Context switch time[us]
350
uc. -s 16k
uc. -s 1k
uc. -s 0k
300
250
200
150
100
50
0
2
4
6
8
10
Processes
12
14
16
Basic Performance
Linux 2.6.7
uClinux 2.6.7
Note
Boot-time
(ms)
437.11
415.16
start_kernel
 shell
Kernel size
(KB)
876
728
Memory size
(KB)
1428
1200
Shell is
different