Aaron » Uncategorized

Block-level Inline Data Deduplication in ext3

aaron — Mon, 20 Dec 2010 06:29:25 +0000

For our class project in advanced operating systems, Kris and I took our first foray into Linux kernel programing. We added block deduplication to ext3, a popular filesystem for Linux. The goal is to reduce the number of writes and to save space on the disk. This could be useful for Solid State Disks, where writes are slow and disk space is expensive. Our code is a bit buggy, but the idea has potential.

Programming Contest: 2nd place in region

aaron — Sat, 06 Nov 2010 06:10:42 +0000

My team placed 2nd in the North Central North America Region of the ACM International Collegiate Programing Competition! We’ve also advanced to the world finals on March 3rd in Sharm El Sheikh, Egypt.

Benchmarking Linux And Hardware

aaron — Mon, 04 Oct 2010 00:36:05 +0000

Modern operating systems provide abstractions of hardware to make programming easier. However, it can be possible to learn some details about the hardware using simple benchmarks running in userspace. I wrote some of these benchmarks in C to measure these things on my computer:

The cost of a context switch in Linux
The size of the TLB and the cost of a TLB miss
The seek time and rotational delay of a hard drive.

Context Switch

For this test, I create several processes and have each one call sched_yield() 100000 times. Each call yields the processor and thus causes a context switch. If you compare this to the time needed to just create the processes, you can get a rough idea of how long a context switch takes. It’s about 1350ns on the test computer.

TLB

Here I iteratively access more and more pages in each test until there is a jump in the average read time. On the test computer, it looks like the TLB has 64 entries and it takes about 4.5ns to handle a TLB miss.

Hard Drive

I found seek time and rotational delay by doing random reads across the disk, and recording the time and distance between reads. My disk is a 4200rpm, so rotational delay is about 14ms. Seek time ranges from 5ms to 20ms, depending on the distance between reads.

If instead you do sequential reads across the disk, but increase the distance between reads by 1 block each time, you get more information.

You can read about the correct way to interpret these disk measurements in Talagala, Arpaci-Dusseau, Patterson.

Modern Algebra Notes

aaron — Wed, 05 May 2010 00:30:15 +0000

modern algebra notes (PDF)
modern algebra notes (lyx)

There are probably some errors. I used LyX to make this note sheet.

Image Epitomes

aaron — Mon, 26 Apr 2010 20:27:07 +0000

An image can be condensed into an epitome, which captures the essence and statistically significant features of the image. I created some matlab code based on Vincent Cheung’s examples that can be used for super-resolution. Here is an example result:

High resolution sample image

Epitome for sample image

The epitome itself may not be very interesting, however, it can be used to reconstruct details of a degraded image.

Original low resolution image

Image after being reconstructed with above epitome

Programming Contest: 10th place in region

aaron — Sat, 31 Oct 2009 03:09:49 +0000

My team placed 10th out of 201 in the North Central North America region for the ACM International Collegiate Programming Contest.

Presentation Studio Theme Editor

aaron — Sat, 29 Aug 2009 17:49:59 +0000

Solidworks is a popular 3D CAD software suite. An existing plugin for Solidworks allows users to export a 3D model as a 3D PDF document. However, there were only four templates available for the layout and style of the PDF. During my internship at Solidworks Labs, I created Presentation Studio Theme Editor, which allows users to create their own templates. Some of its features are:

What you see is what you get
Drag and resize elements with snapping
Z-ordering
Context pop-up bars
Undo and redo
Drag and drop images and text