A FORMAL APPROACH TO PROTOCOL OFFLOAD FOR WEB SERVERS By Juan Manuel Sol¶a-Sloan A thesis submitted in partial ful¯llment of the requirements for the degree of DOCTOR OF PHILOSOPHY in COMPUTING INFORMATION SCIENCE AND ENGINEERING UNIVERSITY OF PUERTO RICO MAYAGUEZÄ CAMPUS May, 2009 Approved by: Nayda G. Santiago-Santiago, Ph.D Date Member, Graduate Committee Manuel Rodr¶³guez-Mart¶³nez,Ph.D Date Member, Graduate Committee Domingo Rodr¶³guez-Rodr¶³guez,Ph.D Date Member, Graduate Committee Isidoro Couvertier-Reyes, Ph.D Date President, Graduate Committee Dorial Castellanos-Rodr¶³guez,Ph.D Date Representative of Graduate Studies Nestor Rodr¶³guez-Rivera, Ph.D Date Chairperson of the Department ABSTRACT The use of networks as computational tools has been fundamental in Com- puter Information Science and Engineering research. As computers have evolved, the demands for faster data transmission have incremented. Protocol processing and application processing compete for a share of CPU time when the underlying network evolves. O²oad Engines have been proposed as ways to alleviate the CPU of the host of the cost of processing the protocols used in an end-to-end communication. These engines are proposed as part of the network interface hardware or as a component near or even inside the CPU. However, an increase in performance is not guaranteed after the installation of this type of engine. The operating system of the host is capable of processing the protocols faster than the engine in some particular occasions. A probabilistic model that estimates the performance metrics of utilization and delay, before and after extracting the protocol processing from the CPU of the host is presented in this document. This novel approach focuses on solving the issues presented by abstracting the inherent characteristics of protocol processing. A test bed was setup to validate the analytical model. The test bed was designed using an emulation-based approach mixed with a real implementation to reproduce the behavior of a TCP O²oad Engine installed as part of a server that runs Apache 2.2. The ¯le system used for populating the Web server has been divided into ¯ve di®erent classes based on its sizes. Each ¯le class has been requested using benchmarks to stress the server in di®erent ways. The analysis of the results obtained shows that the analytical model estimates the utilization and delay of the system. The analysis shows that, for some cases, ii the inclusion of an o²oad engine improves overall system performance. The in- clusion of the model into the operating system can be used to determine when and which objects are going to be handled by the o²oad engine and which are going to be handled by the operating system. Also, by using our model, we can provision the operating system with the capability of balancing the load between the o²oad engine and the host. iii RESUMEN El uso de redes como instrumentos de investigaci¶onha sido fundamental en Ciencias e Ingeniera de la Informaci¶ony la Computaci¶on. La demanda por una transmisi¶onde datos m¶asr¶apidaha incrementado gracias a la evoluci¶onen la computaci¶on. El procesamiento de los protocolos de comunicaci¶onas¶³como el procesamiento de programas de aplicaci¶oncompiten por una fracci¶onde tiempo del procesador principal cuando la red que transmite los datos evoluciona de una velocidad menor a una mayor. Los motores de descarga1 han sido propuestos como una alternativa para aliviar al procesador principal del computador an¯tri¶ondel costo de procesar los protocolos de comunicaci¶on.Estos motores pueden ser incluidos como un equipo adicional que se a~nadea la tarjeta de red o como un componente cerca, o dentro, del procesador principal. Sin embargo, un aumento en el desempe~nodel com- putador no est¶agarantizado despu¶esde la instalaci¶onde un motor de descarga. El sistema operativo del computador an¯tri¶ones capaz de procesar los protoco- los de comunicaci¶onm¶asr¶apidoque el motor de descargue en algunas ocasiones particulares. Un modelo probabil¶³stico que estima utilizaci¶ony demora, antes de y despu¶esde extraer el procesamiento de los protocolos de comunicaci¶ondel procesador principal, se presenta en este documento. Este enfoque novedoso se centra en resolver los asuntos expuestos representando en el modelo anal¶³ticolas caracter¶³sticasinherentes del procesamiento de los protocolos de comunicaci¶on.El 1 \O²oad Engines" iv modelo anal¶³ticofue validado utilizando un experimento. Nuestra base experimen- tal fue dise~nadautilizando un enfoque basado en la emulaci¶ony complementado con una implementaci¶onreal que reproduce la conducta de un motor de descarga de TCP/IP instalado como parte de un servidor que corre Apache 2.2. El sis- tema de archivos que se utiliz¶opara poblar el servidor de Web ha sido dividido en cinco clases que est¶anbasadas en el tama~nodel archivo. Archivos de cada clase fueron solicitados del servidor de Web utilizando los programas de est¶andarde comparaci¶on ("benchmarks") de diferentes maneras. El an¶alisisde los resultados expone que el modelo anal¶³ticoestima la uti- lizaci¶ony la demora del sistema. El an¶alisismuestra, que para algunos casos, la inclusi¶onde un motor de descarga mejora el desempe~nogeneral del sistema. La inclusi¶ondel modelo como parte del sistema operativo puede ser utilizada para determinar cuando y cuales objetos ser¶anmanejados por el motor de descarga y que ser¶amanejado por el sistema operativo. Tambi¶en,utilizando nuestro modelo, se le puede proveer al sistema operativo con la capacidad de equilibrar la carga entre el motor de descarga y el procesador principal del computador an¯tri¶on. v Copyright °c 2009 by Juan Manuel Sol¶a-Sloan Dedication This dissertation is dedicated to the ones with character, courage, conviction, determination, and strength.... For those that are true to their ideals and convic- tions and not the ones imposed by others. For all of you my brothers and sisters, I raise my sword into the wind. ACKNOWLEDGMENTS First of all, I want to thank the NSF and the PRECISE program at CECORD, coordinated by Dr. Domingo Rodr¶³guezand Dr. Nestor Rodr¶³guezfor the ¯nancial support during the ¯rst years of this reasearch. Also, I want to thank the AGEP program of the University of Puerto Rico and its coordinator Dr. Manuel G¶omez of the Rio Piedras campus for their support. I specially want to thank Dr. Isidoro Couvertier for informally drafting me as his Ph.D. student on July 2001. Also I want to thank my graduate committee: Dr. Manuel Rodr¶³guez, Dr. Nayda Santiago, and Dr. Domingo Rodr¶³guez. Also I want to thank Dr. Yi Qian for being part of my committee during my ¯rst years at the Ph.D. program. I would like to extend special thanks to my immediate family and my relatives Elda and Hiram Gay for their support during my ¯rst year at the CISE Ph.D. program. I would like to thank the following people for helping me during this research. First of all, Dr. Jos¶eVega Vilca of the Institute of Statistics of the University of Puerto Rico at Rio Piedras for the invaluable time he spent reviewing and commenting on the mathematical model. He should be the ¯fth member of the committee. Also I would like to thank Dr. Hector J. Huyke and Dr. William Frey for their advise and comments on the ethics chapter. Also I like to thank Dr. Ram¶onV¶asquezEspinosa and Dr. Edgar Acu~nafor guiding me. I would like to thank Luis Ortiz Ortiz and Jos¶eVega Vilca for being my studying partners during my preparation for the qualifying examination. viii Also I liked to thank the following professors for being an inspiration to me during my early years: Ricardo Coronado, Jose J. D¶³az-Caballero,Filiberto Arniel- las and Ismael Garc¶³a. Also, I want to thank my friends from the Humanities department and from Pluriverso: Dr. Luis Pab¶on,William Rios, Dr. Javier Vil- lalonga and Francisco Garc¶³a. Also I would like to thank Urayo¶anCamacho and Rafael Linero for their help during tough times. Also I would like to thank the following people for their emotional support: Jaime Alfonso Alcover, Octavio Rodr¶³guez, Jos¶eV¶elezand the Morales family, and attorneys: Nelson Rodr¶³guez,Jes¶usRivera Delgado and Arturo Negr¶onJr. The following were the people that help in maintaining my sanity during tough times. First of all, my other half, Jeyka Laborde P¶erezfor her uncondi- tional love. Special thanks to Dr. Francisco O'Neil Sulsona for his therapies and recommendations. I would like to thank the underground heavy metal community for encouraging me into staying on the program and not quitting. THANKS TO ALL OF YOU... ix TABLE OF CONTENTS page ABSTRACT ENGLISH ............................. ii ABSTRACT SPANISH ............................. iv ACKNOWLEDGMENTS ............................ viii LIST OF TABLES ................................ xiii LIST OF FIGURES ............................... xiv LIST OF ABBREVIATIONS .......................... xvi LIST OF SYMBOLS ............................... xviii 1 INTRODUCTION ............................. 1 1.1 Motivation .............................. 2 1.2 Problem De¯nition ......................... 4 1.3 Contributions and Signi¯cance ................... 5 1.4 Marginal Contributions ....................... 7 1.5 Dissertation Overview ....................... 7 2 SURVEY OF LITERATURE ....................... 9 2.1 Analytical Modeling ......................... 9 2.1.1 Limitations of Classic Modeling .............. 9 2.1.2 Novel Approaches of Analytical Modeling ......... 10 2.1.3 Innovations on Web Tra±c Modeling ........... 13 2.1.4 Innovations in Characterizing File Sizes and Burst Lengths 14 2.1.5 Linear and other models .................. 16 2.1.6 Summary ........................... 17 2.2 Experimental Research ....................... 18 2.2.1 State of the Art ....................... 18 2.2.2 O²oad Engine Technology Issues ............. 19 2.2.3 TCP and IP Processing Issues ..............