Featured Research

from universities, journals, and other organizations

Software may be able to take over from hardware in managing caches

Date:
September 13, 2013
Source:
Massachusetts Institute of Technology
Summary:
It may be time to let software, rather than hardware, manage the high-speed on-chip memory banks known as "caches."

In today's computers, moving data to and from main memory consumes so much time and energy that microprocessors have their own small, high-speed memory banks, known as "caches," which store frequently used data. Traditionally, managing the caches has required fairly simple algorithms that can be hard-wired into the chips.
Credit: Illustration: Christine Daniloff/MIT

In today's computers, moving data to and from main memory consumes so much time and energy that microprocessors have their own small, high-speed memory banks, known as "caches," which store frequently used data. Traditionally, managing the caches has required fairly simple algorithms that can be hard-wired into the chips.

Related Articles


In the 21st century, however, in order to meet consumers' expectations for steadily increasing computational power, chipmakers have had to begin equipping their chips with more and more cores, or processing units. And as cores proliferate, cache management becomes much more difficult.

Daniel Sanchez, an assistant professor in MIT's Department of Electrical Engineering and Computer Science, believes that it's time to turn cache management over to software. This week, at the International Conference on Parallel Architectures and Compilation Techniques, Sanchez and his student Nathan Beckmann presented a new system, dubbed Jigsaw, that monitors the computations being performed by a multicore chip and manages cache memory accordingly.

In experiments simulating the execution of hundreds of applications on 16- and 64-core chips, Sanchez and Beckmann found that Jigsaw could speed up execution by an average of 18 percent -- with more than twofold improvements in some cases -- while actually reducing energy consumption by as much as 72 percent. And Sanchez believes that the performance improvements offered by Jigsaw should only increase as the number of cores does.

Location, location, location

In most multicore chips, each core has several small, private caches. But there's also what's known as a last-level cache, which is shared by all the cores. "That cache is on the order of 40 to 60 percent of the chip," Sanchez says. "It is a significant fraction of the area because it's so crucial to performance. If we didn't have that cache, some applications would be an order of magnitude slower."

Physically, the last-level cache is broken into separate memory banks and distributed across the chip; for any given core, accessing the nearest bank takes less time and consumes less energy than accessing those farther away. But because the last-level cache is shared by all the cores, most chips assign data to the banks randomly.

Jigsaw, by contrast, monitors which cores are accessing which data most frequently and, on the fly, calculates the most efficient assignment of data to cache banks. For instance, data being used exclusively by a single core is stored near that core, whereas data that all the cores are accessing with equal frequency is stored near the center of the chip, minimizing the average distance it has to travel.

Jigsaw also varies the amount of cache space allocated to each type of data, depending on how it's accessed. Data that is reused frequently receives more space than data that is accessed infrequently or only once.

In principle, optimizing cache space allocations requires evaluating how the chip as a whole will perform given every possible allocation of cache space to all the computations being performed on all the cores. That calculation would be prohibitively time-consuming, but by ignoring some particularly convoluted scenarios that are extremely unlikely to arise in practice, Sanchez and Beckmann were able to develop an approximate optimization algorithm that runs efficiently even as the number of cores and the different types of data increases dramatically.

Quick study

Of course, since the optimization is based on Jigsaw's observations of the chip's activity, "it's the optimal thing to do assuming that the programs will behave in the next 20 milliseconds the way they did in the last 20 milliseconds," Sanchez says. "But there's very strong experimental evidence that programs typically have stable phases of hundreds of milliseconds, or even seconds."

Sanchez also points out that the new paper represents simply his group's "first cut" at turning cache management over to software. Going forward, they will be investigating, among other things, the co-design of hardware and software to improve efficiency even further and the possibility of allowing programmers themselves to classify data according to their memory-access patterns, so that Jigsaw doesn't have to rely entirely on observation to evaluate memory allocation.

"More and more of our computation is happening in data centers," say Jason Mars, an assistant professor of computer science at the University of Michigan. "In the data-center space, it's going to be very important to be able to have the microarchitecture partition and allocate resources on an application-by-application basis."

"When you have multiple applications that are running inside a single box," he explains, "there's a point of interference where jobs can hurt the performance of each other. With current commodity hardware, there are a limited number of mechanisms we have to manage how jobs hurt each other."

Mars cautions that a system like Jigsaw dispenses with a layer of abstraction between chip hardware and the software running on it. "Companies like Intel, once they expose the microarchitectural configurations through the software layer, they have to keep that interface over future generations of the processor," Mars says. "So if Intel wanted to do something audacious with the microarchitecture to make a big change, they'll have to keep that legacy support around, which can limit the design options they can explore."

"However," he adds, "the techniques in Jigsaw seem very practical, and I could see some variant of this hardware-software interface being adopted in future designs. It's a pretty compelling approach, actually."


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Larry Hardesty. Note: Materials may be edited for content and length.


Cite This Page:

Massachusetts Institute of Technology. "Software may be able to take over from hardware in managing caches." ScienceDaily. ScienceDaily, 13 September 2013. <www.sciencedaily.com/releases/2013/09/130913114036.htm>.
Massachusetts Institute of Technology. (2013, September 13). Software may be able to take over from hardware in managing caches. ScienceDaily. Retrieved December 19, 2014 from www.sciencedaily.com/releases/2013/09/130913114036.htm
Massachusetts Institute of Technology. "Software may be able to take over from hardware in managing caches." ScienceDaily. www.sciencedaily.com/releases/2013/09/130913114036.htm (accessed December 19, 2014).

Share This


More From ScienceDaily



More Computers & Math News

Friday, December 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Navy Unveils Robot Fish

Navy Unveils Robot Fish

Reuters - Light News Video Online (Dec. 18, 2014) The U.S. Navy unveils an underwater device that mimics the movement of a fish. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
How 2014 Shaped The Future Of The Internet

How 2014 Shaped The Future Of The Internet

Newsy (Dec. 18, 2014) It has been a long, busy year for Net Neutrality. The stage is set for an expected landmark FCC decision sometime in 2015. Video provided by Newsy
Powered by NewsLook.com
White House: Sony Hack a 'serious National Security Matter'

White House: Sony Hack a 'serious National Security Matter'

AFP (Dec. 18, 2014) White House spokesperson Josh Earnest says cyber attacks that ultimately prompted Sony Pictures to scrap the release of a madcap comedy about North Korea are a "serious national security matter." Duration: 00:35 Video provided by AFP
Powered by NewsLook.com
Google Maps Lets You Tour Street View in Virtual Reality

Google Maps Lets You Tour Street View in Virtual Reality

Buzz60 (Dec. 18, 2014) Google Maps now lets Android users see cities on Street View in virtual reality with the special Cardboard feature. Sean Dowling (@Seandowlingtv) has the details. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins