The document discusses 'zero copy' data transfer, which allows for data movement from disk to user buffers without involving the operating system's kernel, resulting in fewer data copies and context switches. It contrasts traditional data transfer practices with zero copy methods, showcasing a significant performance boost of approximately 65%. Limitations include its suitability only for static content and inability to modify or append data during transfer.

1. Zero Copy: A Green Approach
to Data Transfer
Pramod B Nagaraja
IBM India Pvt LTD

2. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice

Performance Comparison

Application Scenario

Limitations

Conclusion

3. What is Zero Copy ?
•
Data transfer from disk to user buffers without
an intermediate copy into OS Kernel buffers
•
Computer operations in which CPU does not
perform the task of copying data from one
memory area to another
• DMA
• MMU

4. What is Zero Copy ?
•
Fewer intermediate Data Copies, fewer
context switches
•
Linux :: sendfile, sendfile64

5. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice

Performance Comparison

Application Scenario

Limitations

Conclusion

6. Application Scenario

7. Data Transfer : Age-Old Practice
File.read(fd, buf, len);
Socket.send(socket, buf, len);
inputStream = new FileInputStream(fname);
output = new
DataOutputStream(socket.getOutputStream());
byte[] b = new byte[4096];
long read = 0, total = 0;
while((read = inputStream.read(b))>=0) {
total = total + read;
output.write(b);
}

8. Data Transfer : Age-Old Practice

4 Data Copies

9. Data Transfer : Age-Old Practice

4 Context Switches

10. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice

Performance Comparison

Application Scenario

Limitations

Conclusion

11. Data Transfer : Best Practice

FileChannel Approach
java.nio.channels.FileChannel.transferTo(pos, cnt, writableChannel);
SocketChannel sc = SocketChannel.open();
sc.connect(sad);
FileChannel fc = new
FileInputStream(fname).getChannel();
long nsent = 0, curnset = 0;
curnset = fc.transferTo(0, fsize, sc);

12. Data Transfer : Best Practice
 3 Data Copies

13. Data Transfer : Best Practice
 2 Context Switches

14. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice
•
Performance Comparison

Application Scenario

Limitations

Conclusion

15. Performance Comparison
• ~ 65% Performance Boost up !
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
63
M B
350
M B
1
GB
Traditio
nal
FileCha
nnel
Measurements take on Linux (xi32) with 2.6 kernel

16. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice

Performance Comparison
•
Application Scenario
•
Limitations
•
Conclusion

17. Application Scenario

FTP Servers

Web Servers

Mail Servers

Any Applications serving static content

18. Agenda

Zero Copy

Data Transfer : Age-Old Practice

Data Transfer : Best Practice

Performance Comparison

Application Scenario
•
Limitations
•
Conclusion

19. Theoretically Speaking there is no difference
b/w Theory and Practice .. but in Practice
there is !!

20. Limitations

Suitable only for static content

Not suitable if Data to be transferred needs to
be modified/appended with/appended to, etc

FileChannels can only be used to transfer
data from File to File, File to Socket objects.

21. References

More details can be found @
http://www.ibm.com/developerworks/library/j-
zerocopy/index.html

http://www.linuxjournal.com/article/6345

22. Q&A

23. Thank You !!!!