Skip to main content

Reason for getting less Network performance In Linux-2.6.20.9

By

Packets can be sent out immediately with out a delay if it falls under below reasons and without violation of Nagle’s rules

Ø It is full sized.

Ø Or it contains FIN. (Already checked by caller)

Ø Or TCP_NODELAY was set.

Ø Or TCP_CORK is not set, and all sent packets are ACKed. With Minshall's modification: all sent small packets are ACKed.

The reason for getting less Network performance In Linux-2.6.20.9 is as follows.

If we have TSO enabled and if we an 8KB of data to be transmitted, In this case what the TCP/IP stack does is as follows.

STEP1: 8KB of data will be copied from Application to the Kernel Buffer

STEP2: Before forming the TCP segment Nagle’s test will be done, this will be done only if TSO_SEGS is equal to 1. This variable tells the HW to how many chunks this 8kB has to be divided while sending it out on the wire. For Example: IF 8KB of data is to be transmitted and if your MSS is 1448 then your tso_segs will be 6 (i.e. 8192 /1448 ~= 6).

STEP3: TCP/IP stack will only give data of length which is multiple of MSS, i.e., if you have 8KB of data and your max segment size is 1448 then in this case the amount of data that has sent out will be calculated as follows

Amount of data to be sent out = 8192 – (8192 mod 1448)

= 8192 – 952

= 7240

As a result of this only 7240 out of 8192 will be sent out, the remaining amount of data that is 952 will be sent out later as new TCP/IP segment. That is it as fall through again from step2.

STEP4: TCP/IP header will formed successfully for the data of length 7240 and it will be given to the Network driver for sending it out on the wire.

This remaining amount of data 952 bytes will be tried to send out, it will start from step2 again; in this case the tso_segs value will be 1, as a result of this it has to go for Nagel’s test. Since it is not a full sized packet nagle’s test will be failed and the packet will be delayed in sending out. As a result of this we were getting less performance in 2.6.20.9.

This can be avoided by committing the Trimming of data in step3 as our H/W as the feature of handling the entire 8k even if the last chunk is less than MSS or this can also be avoided by disabling Nagle’s algorithm.

Nagle’s algorithm can be disabled by using setsockopt

Labels:

Comments

Post a Comment

Popular posts from this blog

Rajasthan Board 10th Results | rajedubord.nic.in | RBSE

By
Raj Board of Secondary Education, Rajasthan Results at rajeduboard.nic.in Board of Secondary Education, Rajasthan Ajmer declared result of secondary examination today at 4PM official site is rajedubord.nic.in check Secondary Examination- 2008 Result (To be announced on July 1st, 2008 at 4:00 PM) source http:// rajresults.nic.in / Declared result Praveshika Examination-2008 Result (Announced on June 25, 2008 at 4:00 PM) The history of the Board of Secondary Education Rajasthan (BSER) is a remarkable panorama of progressive record of the futurological vision for developing a dynamic system of various sub-systems of examinations and highlights of the academic excellence of the last four decades. The BSER took rapid strides for promotion and development of Secondary Education in Rajasthan, spread over 3,42,239 sq. km. and in more than 6000 schools located in 32 districts involving 8.5 lakhs students for Secondary and Senior Secondary Examination in the year 2000. At present the Board is ...
Post a Comment
Read more

ahsec results 2008 | www.ahsec.nic.in

By
The official website of assam higher secondary education council Results of Assam is down seems they are uploading results , direct link to check ahsec results 2008 is http://resultsassam.nic.in/index.asp You can find results of AHSEC at the link above. current page The Website www.ahsec.nic.in Designed Developed & Hosted by NIC, Assam State Centre, Guwahati is down for result uploading. keep checking this page, I will update as soon as news comes. All the best to AHSEC - assam higher secondary education council students. Direct links http://assam.nic.in/ www.ahsec.nic.in http://resultsassam.nic.in/
Post a Comment
Read more

Encyclopedia of Life - by the World's Leading Scientists

By
An epic effort to promote biodiversity and document all 1.8 million named species on the planet. When completed, http://www.eol.org will serve as a global biodiversity tool, providing scientists, policymakers, students, and citizens information they need to discover and protect the planet and encourage learning and conservation. The Encyclopedia of Life is a collaborative scientific effort led by the Field Museum of Natural History, Harvard University, Marine Biological Laboratory, Missouri Botanical Garden, Smithsonian Institution, and Biodiversity Heritage Library, a consortium including the core institutions and also the American Museum of Natural History (New York), Natural History Museum (London), New York Botanical Garden, and Royal Botanic Gardens (Kew). clipped from www.eol.org clipped from www.eol.org "Imagine an electronic page for each species of organism on Earth, available everywhere by single access on command." - Edward O. Wilson The Encyclopedia of Life (E...
Post a Comment
Read more