Processors are unquestionably at the heart of every computer, handling countless instructions and shuffling data at speeds unimaginable just a few years ago. But although processors are critical elements of any desktop or workstation, server systems frequently demand the highest levels of performance. Corporate servers must often service hundreds (even thousands) of users through shared applications, Web services, and other support tasks such as email storage. Increasing performance demands are quickly leading to multiprocessor platforms where each processor handles a large number of threads. For a network, such operation is a key to the future.



Something Borrowed

Sun's line of UltraSPARC processors has enjoyed a long and leading role in high-performance server platforms. However, as IT demands increase, Sun believes that processor designs should be tailored to better serve the complex, multithreaded environment that is so common in servers, rather than wringing ever-more megahertz through a single-threaded chip. This notion of "multithreading performance over raw speed" is the underlying concept behind Sun's Throughput Computing roadmap.

However, chip designs are a notoriously difficult and expensive undertaking, especially for sophisticated processors. Marc Tremblay, chief architect of Sun's Scalable Systems Group, says that Niagara was actually the result of an acquisition intended to speed the introduction of a new processor. "We have been on the path of Throughput Computing for nine years through a variety of projects and products. In 2002 we evaluated a company named Afara and decided to acquire it because we felt we could get to the third generation of CMT [chip multithreading] products more quickly. We made major modifications to the original design, including going to 90nm as opposed to 130nm, and after roughly two years, taped out [created chip prototypes for] Niagara."



Counting Threads

Tremblay says that Niagara's CMT was not simply an extension or modification of single-threaded chip designs. Instead, the entire processor was designed from the ground up with features that favor multithreading operation. "The key feature is the level of CMT offered. Intel and AMD have announced plans to ship a dual-core chip in the 90nm generation. In the same generation, we will be shipping a 32-thread chip at a fraction of the power dissipated by these dual cores." Ultimately, this results in significant performance and power differences. "The main difference here is the fact that the pipeline, the switch, the memory subsystem, etc. were all designed with CMT in mind, as opposed to designing a single-threaded pipeline and try to make it a CMT in 90nm [chip fabrication processes]." Although no performance data was available at press time, expect to see more detailed data as Niagara-based systems become available.

Tremblay points out that disruptive CMT could potentially have a positive impact. "Disruptive CMTs, with tens of threads, should, in general, do well in markets where SMPs, say 32-way, and horizontal systems are currently used. The key is that one can either run threads or processes on each one of these 32 hardware thread contexts. Obviously if there is a possibility to share code or data, CMTs will do even better. With server-room wide load balancers, we expect this to make CMTs systems pervasive [in the IT industry]." Tremblay says that Niagara-based systems should enable a new category of network applications and lower the costs of delivering current network applications.



Getting Ready

Niagara should help customers tackle their current problems without requiring substantial new investments (other than the systems). "The industry certainly has responded very positively to the early disclosures on Niagara. It is disruptive, and it solves customers' problems, as opposed to requiring new applications, new compilers, etc." Sun expects to ship Niagara-based systems in early 2006, but the availability of Niagara chips is not yet confirmed. This means third-party developers will have to wait a bit longer before working with Niagara chips.

Although Niagara-based systems are more than a year away, Tremblay says that it's not too early for network planners and administrators to begin some groundwork in preparation for possible CMT systems. "Understanding that chips with tens of threads are coming into systems in early 2006 should help IT planners and administrators architect their server rooms and also should help them in discussions with ISVs." Early investigations into application compatibility and performance needs now may help to ease the adoption of such CMT systems in the future.

by Stephen J. Bigelow