The Webpage of Girish Venkatasubramanian

(Updated on May 1, 2011 )

Resume

Research

Publications

Industrial Experience

Academics

Awards and Honors

             

Contact Information

336 B (P.O. Box: 116200, 339), Larsen Hall
Gainesville, FL 32601
Tel (O): (352) 392-8705

E-mail: GIRISHVS AT UFL DOT EDU (All lower case)    
 

I am a PhD graduate from the Department of Electrical and Computer Engineering, University of Florida, Gainesville. I am an alumnus of the Advanced Computing and Information System Lab, where I was advised by Dr. Renato Figueiredo. I completed my Bachelor of Engineering from P.S.G College of Technology, Coimbatore, India (2003) and my Master of Science from University of Florida (2005).

I am currently a member of the Hybrid Computing Group at Intel Labs, Santa Clara, California.

Resume

Resume: PDF format (outdated, email for updated copy) 

Research

During my PhD, I conducted research in the areas of computer architecture, virtualization and full-system modeling & simulation. I have also worked on designing Fault-tolerant Nanoscale Memories. Here's a list of the significant projects I have worked on. (Unless mentioned otherwise, I am the sole architect and developer on these projects)

A simulation framework for the analysis of TLB behavior

To understand the performance impact of the TLB and to investigate the performance improvement due to various architectural modifications, a suitable full-system framework which models the x86 ISA at the micro-operation level and supports customizable tagged TLB models. I developed such a simulation framework using Simics and FeS2 and adding full-fledged tagged TLB models on top of this framework. This is the first academic simulator that is capable of simulating consolidated virtualized workloads in a full-system framework. This simulation framework was the focus of an interview by Jakob Engblom of Windriver Simics. The interview can be found here or a PDF version can be accessed here.

 

TMT - A Tag Management Framework for Translation Lookaside Buffers

The Tag Manager Table (TMT) is a low-latency software-transparent hardware solution for generation and management of tags for hardware-managed TLBs (like on x86) in order to improve the performance of virtualized workloads. Unlike VM-specific tags (ASIDs), the TMT uses process-specific identifiers for tagging TLB entries and avoids TLB flushes during both inter-VM and intra-VM context switches. From simulation based results, it is found that the TMT-generated tags can reduce the number of flushes by about 90% compared to no tags. For 8-way associative TLBs, this reduces the TLB miss rates by 65% to 90% and results in a 4.5% to 25% improvement in the IPC of virtualized workloads.

 

In addition, the TMT may be seamlessly used for non-virtualized workloads as well to reduce 80% to 90% of the TLB-induced performance slowdown. The TMT can also be used as a generic tagging framework for enabling shared Last Level TLBs or for tagging I/O TLBs.

 

CShare TLB - Controlled Sharing of Tagged Translation Lookaside Buffers

With the emergence of TLB tags to facilitate caching the entries of multiple address spaces, the TLB has become a performance-critical shared platform resource. The CShare TLB architecture is proposed to isolate the TLB behavior of virtualized workloads from one another using a TLB Sharing Table (TST) along with the TMT. The CShare TLB may also be used to increase the IPC of consolidated workloads or selectively enhance the IPC of one component workload by controlling the amount of shared TLB space used by the different VMs running these workloads. The performance of a high priority workload due to using the TMT without controlled sharing can be further improved by 1.4X using such TLB usage restrictions. The CShare TLB can be used with both static and dynamic usage control policies.

 

Archer

I am a part of the team working on the NSF ARCHER project. I am responsible for customizing the Archer VM disk by populating it with architectural simulation tools like SESC, PTLSim, FeS2, Pin and Simics and for producing manuals for using these tools on the Archer infrastructure.

 

NanoMAP

Crossbar Nanoscale Memories consisting of non volatile memory elements at the crosspoints of a grid of nanowires is touted as the next paradigm in high density memory design. Such memories formed by methods like stocahstic selection comprise an address space which is far greater than the log2N address space (N wires will have log2N bit address). Hence, a mapper which translates from a log2N address space to the actual addresses and interfaces the memory to the microscale circuitry is needed. NanoMAP is a mapper which uses a hierarchical approach, where the nth stage maps from the log2N space to the n-1th stage and the 1st stage maps from the 2nd stage to the nanoscale memory. With a good choice of the number of stages, the size of the total interface module can be brought down to 3% to 5% the size of a one-stage microscale mapper.

 

Moreover, apart from the usual constraints in terms of Area, Power and Speed, Reliability has emerged as one of the important limitations in these memories. The NanoMAP model also comprises an analytical model for the reliability of a nanoscale memory. The defects being considered are unclustered hard defects and the fault tolerance mechanism is ECC with reconfiguration using spares. Using this model, the variation of reliability with redundancy allocation is also studied.

 

Reconfigurable Computing Cluster

I developed a communication mechanism among RC boards in a cluster using MPI and architected a prototype of such a cluster. I adapted parallel cluster benchmarks and developed performance metrics for measuring RC cluster systems.

 

Other Class Projects

A selection from the projects I have done for my coursework.

 

Publications

  1. Venkatasubramanian, G .; Figueiredo, R.J., "A Nanoscale Memory Interface Scheme based on Hierarchical Memory Mapping ,"Sixth IEEE Conference on Nanotechnology (Nano '06), June 2006
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  3. Venkatasubramanian, G.; Boykin, P.O.; Figueiredo, R.J., "Design of high-yield defect-tolerant self-assembled nanoscale memories," IEEE International Symposium on Nanoscale Architectures (Nanoarch '07), Oct. 2007 (Acceptance Rate: ~33%)
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  5. Venkatasubramanian, G.; Figueiredo, R.J.; Illikkal, R.; Newell, D., "A Simulation Analysis of Shared TLBs with Tag Based Partitioning in Multicore Virtualized Environments," Workshop on Managed Multi-Core Systems (MMCS '09) (in conjunction with ASPLOS 2009), Mar. 2009
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  7. Venkatasubramanian, G.; Figueiredo, R.J.; Illikkal, R.; Newell, D., "TMT - A TLB Tag Management Framework for Virtualized Platforms," 21st International Symposium on Computer Architecture and High Performance Computing (SBAC-PAD 2009), Oct. 2009 (Acceptance Rate: 35%)
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  9. Wolinsky, D.; Liu, Y.; St Juste, P.; Venkatasubramanian, G.; Figueiredo, R.J., "On the Design of Scalable, Self-Configuring Virtual Networks," The 21st International Conference for High Performance Computing, Networking, Storage and Analysis (SC '09), Nov. 2009 (Acceptance Rate: 22%)
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  11. Venkatasubramanian, G.; Figueiredo, R.J.; Illikkal, R.; Newell, D., "A Simulation Framework for the Analysis of TLB Behavior in Virtualized Environments," 18th IEEE International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS 2010), Aug. 2010 (Acceptance Rate 16%)
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  13. Venkatasubramanian, G.; Wolinksy, D, Figueiredo, R.J., "Towards Collaborative Research and Education in Computer Architecture with the Archer System," 18th IEEE International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS 2010), Aug. 2010
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  15. Venkatasubramanian, G.; Figueiredo, R.J.; Illikkal, R.; Newell, D., "TMT - A TLB Tag Management Framework for Virtualized Platforms," (Invited) International Journal of Parallel Programming (Link to IJPP official copy)
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  17. Venkatasubramanian, G.; Figueiredo, R.J.; Illikkal, R., "On the Performance of Tagged Translation Lookaside Buffers: A Simulation-Driven Analysis," 19th IEEE International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS 2011), July. 2011 (Selected as one of the top 10 papers in the conference) (Link to IEEE official copy)
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  19. Venkatasubramanian, G., "Tag management architecture and policies for hardware-managed translation lookaside buffers in virtualized platforms," Ph.D Dissertaion, University of Florida, 2011 (Link to Proquest published copy)

Industrial Experience

Graduate Intern at Systems Technology Lab (CTG), Intel Corporation, Hillsboro, Oregon (August to November 2007)

 

Member of Technical Staff Intern at Performance Group, VMware Corporation, Palo Alto, California (September to November 2009)

 

Graduate Intern at Intel Labs (IPR/SPA), Intel Corporation, Hillsboro, Oregon (September to November 2010)

 

Academics

I have a 4.0 GPA for the graduate level courses that I have taken. Some of these are

 

Awards and Honors