MIT news info....
An operating system, whether Windows, the Apple OS, Linux or any other, is software that mediates between applications, like word processors and Web browsers, and those rudimentary bit operations. Like everything else, operating systems will have to be reimagined for a world in which computer chips have hundreds or thousands of cores.
A computer with hundreds or thousands of cores tackling different aspects of a problem and exchanging data offers much more opportunity than an ordinary computer does for something to go badly wrong. At the same time, it has more resources to throw at any problems that do arise. So, says Anant Agarwal, who leads the Angstrom project, a multicore operating system needs both to be more self-aware — to have better information about the computer’s performance as a whole — and to have more control of the operations executed by the hardware.
But crucial to the Angstrom operating system — dubbed FOS, for factored operating system — is a software-based performance measure, which Agarwal calls “heartbeats.” Programmers writing applications to run on FOS will have the option of setting performance goals: A video player, for instance, may specify that the playback rate needs to be an industry standard 30 frames per second. Software will automatically interpret that requirement and emit a simple signal — a heartbeat — each time a frame displays. If the heartbeat fell below 30, FOS could allocate more cores to the video player. Alternatively, if system resources are in short supply, it could adopt some computational short cuts in order to get the heartbeat back up again.
Computer-science professor Martin Rinard’s group has been investigating cases where accuracy can be traded for speed and has developed a technique it calls “loop perforation.” A loop is an operation that’s repeated on successive pieces of data — like, say, pixels in a frame of video — and to perforate a loop is simply to skip some iterations of the operation. Graduate student Hank Hoffmann has been working with Agarwal to give FOS the ability to perforate loops on the fly.
Since Angstrom has the luxury of building a chip from the ground up, it’s also going to draw on work that Kaashoek has done with assistant professor Nickolai Zeldovich to secure operating systems from outside attack. An operating system must be granted some access to primitive chip-level instructions — like Kaashoek’s cache swap command and cache address request. But Kaashoek and Zeldovich have been working to minimize the number of operating-system subroutines that require that privileged access. The fewer routes there are to the chip’s most basic controls, the harder they are for attackers to exploit.
Computer-science professor Srini Devadas has done work on electrical data connections that Angstrom is adopting , but outside Angstrom, he’s working on his own approach to multicore operating systems that in some sense inverts Kaashoek’s primitive cache-swap procedure. Instead of moving data to the cores that require it, Devadas’ system assigns computations to the cores with the required data in their caches. Sending a core its assignment actually consumes four times as much bandwidth as swapping the contents of caches does, so it also consumes more energy. But in multicore chips, multiple cores will frequently have cached copies of the same data. If one core modifies its copy, all the other copies have to be updated, too, which eats up both energy and time. By reducing the need for cache updates, Devadas says, a multicore system that uses his approach could outperform one that uses the traditional approach. And the disparity could grow if chips with more and more cores end up caching more copies of the same data.
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Operating systems for multicore chips will need more information about their own performance — and more resources for addressing whatever problems arise.
Larry Hardesty, MIT News Office.
An operating system, whether Windows, the Apple OS, Linux or any other, is software that mediates between applications, like word processors and Web browsers, and those rudimentary bit operations. Like everything else, operating systems will have to be reimagined for a world in which computer chips have hundreds or thousands of cores.
A computer with hundreds or thousands of cores tackling different aspects of a problem and exchanging data offers much more opportunity than an ordinary computer does for something to go badly wrong. At the same time, it has more resources to throw at any problems that do arise. So, says Anant Agarwal, who leads the Angstrom project, a multicore operating system needs both to be more self-aware — to have better information about the computer’s performance as a whole — and to have more control of the operations executed by the hardware.
But crucial to the Angstrom operating system — dubbed FOS, for factored operating system — is a software-based performance measure, which Agarwal calls “heartbeats.” Programmers writing applications to run on FOS will have the option of setting performance goals: A video player, for instance, may specify that the playback rate needs to be an industry standard 30 frames per second. Software will automatically interpret that requirement and emit a simple signal — a heartbeat — each time a frame displays. If the heartbeat fell below 30, FOS could allocate more cores to the video player. Alternatively, if system resources are in short supply, it could adopt some computational short cuts in order to get the heartbeat back up again.
Computer-science professor Martin Rinard’s group has been investigating cases where accuracy can be traded for speed and has developed a technique it calls “loop perforation.” A loop is an operation that’s repeated on successive pieces of data — like, say, pixels in a frame of video — and to perforate a loop is simply to skip some iterations of the operation. Graduate student Hank Hoffmann has been working with Agarwal to give FOS the ability to perforate loops on the fly.
Since Angstrom has the luxury of building a chip from the ground up, it’s also going to draw on work that Kaashoek has done with assistant professor Nickolai Zeldovich to secure operating systems from outside attack. An operating system must be granted some access to primitive chip-level instructions — like Kaashoek’s cache swap command and cache address request. But Kaashoek and Zeldovich have been working to minimize the number of operating-system subroutines that require that privileged access. The fewer routes there are to the chip’s most basic controls, the harder they are for attackers to exploit.
Computer-science professor Srini Devadas has done work on electrical data connections that Angstrom is adopting , but outside Angstrom, he’s working on his own approach to multicore operating systems that in some sense inverts Kaashoek’s primitive cache-swap procedure. Instead of moving data to the cores that require it, Devadas’ system assigns computations to the cores with the required data in their caches. Sending a core its assignment actually consumes four times as much bandwidth as swapping the contents of caches does, so it also consumes more energy. But in multicore chips, multiple cores will frequently have cached copies of the same data. If one core modifies its copy, all the other copies have to be updated, too, which eats up both energy and time. By reducing the need for cache updates, Devadas says, a multicore system that uses his approach could outperform one that uses the traditional approach. And the disparity could grow if chips with more and more cores end up caching more copies of the same data.
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