Abstract: Each computing node of a distributed computing system may implement a hardware mechanism at the network interface for message driven prefetching of application data. For example, a parallel data-intensive application that employs function shipping may distribute respective portions of a large data set to main memory on multiple computing nodes. The application may send messages to one of the computing nodes referencing data that is stored locally on the node. For each received message, the network interface on the recipient node may extract the reference, initiate the prefetching of referenced data into a local cache (e.g., an LLC), and then store the message for subsequent interpretation and processing by a local processor core. When the processor core retrieves a stored message for processing, the referenced data may already be in the LLC, avoiding a CPU stall while retrieving it from memory. The hardware mechanism may be configured via software.

Abstract: The disclosed embodiments provide a system in which a processor chip accesses an off-chip cache via silicon photonic waveguides. The system includes a processor chip and a cache chip that are both coupled to a communications substrate. The cache chip comprises one or more cache banks that receive cache requests from a structure in the processor chip optically via a silicon photonic waveguide. More specifically, the silicon photonic waveguide is comprised of waveguides in the processor chip, the communications substrate, and the cache chip, and forms an optical channel that routes an optical signal directly from the structure to a cache bank in the cache chip via the communications substrate. Transmitting optical signals from the processor chip directly to cache banks on the cache chip facilitates reducing the wire latency of cache accesses and allowing each cache bank on the cache chip to be accessed with uniform latency.

Abstract: Each computing node of a distributed computing system may implement a hardware mechanism at the network interface for message driven prefetching of application data. For example, a parallel data-intensive application that employs function shipping may distribute respective portions of a large data set to main memory on multiple computing nodes. The application may send messages to one of the computing nodes referencing data that is stored locally on the node. For each received message, the network interface on the recipient node may extract the reference, initiate the prefetching of referenced data into a local cache (e.g., an LLC), and then store the message for subsequent interpretation and processing by a local processor core. When the processor core retrieves a stored message for processing, the referenced data may already be in the LLC, avoiding a CPU stall while retrieving it from memory. The hardware mechanism may be configured via software.

Abstract: The disclosed embodiments provide a system that uses broadcast-based TLB sharing to reduce address-translation latency in a shared-memory multiprocessor system with two or more nodes that are connected by an optical interconnect. During operation, a first node receives a memory operation that includes a virtual address. Upon determining that one or more TLB levels of the first node will miss for the virtual address, the first node uses the optical interconnect to broadcast a TLB request to one or more additional nodes of the shared-memory multiprocessor in parallel with scheduling a speculative page-table walk for the virtual address. If the first node receives a TLB entry from another node of the shared-memory multiprocessor via the optical interconnect in response to the TLB request, the first node cancels the speculative page-table walk. Otherwise, if no response is received, the first node instead waits for the completion of the page-table walk.

Abstract: In a multi-chip module (MCM), optical waveguides in a first plane convey modulated optical signals among integrated circuits (which are sometimes referred to as ‘chips’). Moreover, an optical-butterfly switch, optically coupled to the optical waveguides, dynamically allocates communication bandwidth among the integrated circuits. This optical-butterfly switch includes optical components in the first plane and a second plane, and optical couplers that couple the modulated optical signals to and from the first plane and the second plane. In this way, the MCM communicates the modulated optical signals among the integrated circuits without optical-waveguide crossings in a given plane.

Abstract: The disclosed embodiments provide a system that performs distributed page-table lookups in a shared-memory multiprocessor system with two or more nodes, where each of these nodes includes a directory controller that manages a distinct portion of the system's address space. During operation, a first node receives a request for a page-table entry that is located at a physical address that is managed by the first node. The first node accesses its directory controller to retrieve the page-table entry, and then uses the page-table entry to calculate the physical address for a subsequent page-table entry. The first node determines the home node (e.g., the managing node) for this calculated physical address, and sends a request for the subsequent page-table entry to that home node.

Abstract: The disclosed embodiments provide a system that uses broadcast-based TLB sharing to reduce address-translation latency in a shared-memory multiprocessor system with two or more nodes that are connected by an optical interconnect. During operation, a first node receives a memory operation that includes a virtual address. Upon determining that one or more TLB levels of the first node will miss for the virtual address, the first node uses the optical interconnect to broadcast a TLB request to one or more additional nodes of the shared-memory multiprocessor in parallel with scheduling a speculative page-table walk for the virtual address. If the first node receives a TLB entry from another node of the shared-memory multiprocessor via the optical interconnect in response to the TLB request, the first node cancels the speculative page-table walk. Otherwise, if no response is received, the first node instead waits for the completion of the page-table walk.

Abstract: The disclosed embodiments provide techniques for reducing address-translation latency and the serialization latency of combined TLB and data cache misses in a coherent shared-memory system. For instance, the last-level TLB structures of two or more multiprocessor nodes can be configured to act together as either a distributed shared last-level TLB or a directory-based shared last-level TLB. Such TLB-sharing techniques increase the total amount of useful translations that are cached by the system, thereby reducing the number of page-table walks and improving performance. Furthermore, a coherent shared-memory system with a shared last-level TLB can be further configured to fuse TLB and cache misses such that some of the latency of data coherence operations is overlapped with address translation and data cache access latencies, thereby further improving the performance of memory operations.

Abstract: A network is described in which a base optical point-to-point (P2P) network can be reconfigured to a target network topology. This reconfigurable architecture customizes the network topology for different classes of applications to maximize throughput. In particular, the network can function efficiently at high-radix and low-radix traffic patterns. This capability is obtained using configurable electrical circuit switches at each node in the network. These configurable electrical circuit switches can be set so that incoming packets are directly routed to a specified output (either a local destination or an outgoing optical link) without: delay, contention, or buffers. In this way, predefined network topologies can be configured with improved node-to-node bandwidths when compared to the original P2P network by leveraging unused optical links. Furthermore, because the electrical circuit switches can be reconfigured, the network topology can be dynamically reconfigured to suit applications or application phases.

Abstract: The disclosed embodiments provide a system that uses broadcast-based TLB-sharing techniques to reduce address-translation latency in a shared-memory multiprocessor system with two or more nodes that are connected by an electrical interconnect. During operation, a first node receives a memory operation that includes a virtual address. Upon determining that one or more TLB levels of the first node will miss for the virtual address, the first node uses the electrical interconnect to broadcast a TLB request to one or more additional nodes of the shared-memory multiprocessor in parallel with scheduling a speculative page-table walk for the virtual address. If the first node receives a TLB entry from another node of the shared-memory multiprocessor via the electrical interconnect in response to the TLB request, the first node cancels the speculative page-table walk. Otherwise, if no response is received, the first node instead waits for the completion of the page-table walk.

Abstract: The disclosed embodiments provide techniques for reducing address-translation latency and the serialization latency of combined TLB and data cache misses in a coherent shared-memory system. For instance, the last-level TLB structures of two or more multiprocessor nodes can be configured to act together as either a distributed shared last-level TLB or a directory-based shared last-level TLB. Such TLB-sharing techniques increase the total amount of useful translations that are cached by the system, thereby reducing the number of page-table walks and improving performance. Furthermore, a coherent shared-memory system with a shared last-level TLB can be further configured to fuse TLB and cache misses such that some of the latency of data coherence operations is overlapped with address translation and data cache access latencies, thereby further improving the performance of memory operations.

Abstract: A network is described in which a base optical point-to-point (P2P) network can be reconfigured to a target network topology. This reconfigurable architecture customizes the network topology for different classes of applications to maximize throughput. In particular, the network can function efficiently at high-radix and low-radix traffic patterns. This capability is obtained using configurable electrical circuit switches at each node in the network. These configurable electrical circuit switches can be set so that incoming packets are directly routed to a specified output (either a local destination or an outgoing optical link) without: delay, contention, or buffers. In this way, predefined network topologies can be configured with improved node-to-node bandwidths when compared to the original P2P network by leveraging unused optical links. Furthermore, because the electrical circuit switches can be reconfigured, the network topology can be dynamically reconfigured to suit applications or application phases.

Abstract: An arbitration technique for determining mappings for a switch is described. During a given arbitration decision cycle, an arbitration mechanism maintains, until expiration, a set of mappings from a subset of the input ports to a subset of the output ports of the switch. This set of mappings was determined during an arbitration decision cycle up to K cycles preceding the given arbitration decision cycle. Because the set of mappings are maintained, it is easier for the arbitration mechanism to determine mappings from a remainder of the input ports to the remainder of the output ports without collisions.

Abstract: In a multi-chip module (MCM), integrated circuits are coupled by optical waveguides that convey optical signals. The optical waveguides provide dedicated point-to-point optical links between all pairs of the integrated circuits. Moreover, for a given point-to-point optical link between a given pair of integrated circuits, other integrated circuits in the integrated circuits steal access on the given point-to-point optical link when communicating information to one of the given pair of integrated circuits so that the given point-to-point optical link is shared by more than the given pair of integrated circuits. Furthermore, the integrated circuits recover errors in messages in the optical signals corrupted by collisions on the given point-to-point optical link using erasure coding. In this way, the MCM may provide an optical network with increased bandwidth relative to a point-to-point optical network.

Abstract: An arbitration technique for determining mappings for a switch is described. During a given arbitration decision cycle, an arbitration mechanism maintains, until expiration, a set of mappings from a subset of the input ports to a subset of the output ports of the switch. This set of mappings was determined during an arbitration decision cycle up to K cycles preceding the given arbitration decision cycle. Because the set of mappings are maintained, it is easier for the arbitration mechanism to determine mappings from a remainder of the input ports to the remainder of the output ports without collisions.

Abstract: In a multi-chip module (MCM), first and second optical waveguides convey optical signals among integrated circuits. The first and second optical waveguides may be implemented in a first layer or plane on a substrate. Moreover, bridge chips in a second plane may be used to couple the optical signals between the first or second optical waveguides and the integrated circuits. By using a single layer for optical routing, the MCM may provide a point-to-point network among the integrated circuits without optical-waveguide crossing.

Abstract: The disclosed embodiments provide a system that performs distributed page-table lookups in a shared-memory multiprocessor system with two or more nodes, where each of these nodes includes a directory controller that manages a distinct portion of the system's address space. During operation, a first node receives a request for a page-table entry that is located at a physical address that is managed by the first node. The first node accesses its directory controller to retrieve the page-table entry, and then uses the page-table entry to calculate the physical address for a subsequent page-table entry. The first node determines the home node (e.g., the managing node) for this calculated physical address, and sends a request for the subsequent page-table entry to that home node.

Abstract: The disclosed embodiments provide techniques for reducing address-translation latency and the serialization latency of combined TLB and data cache misses in a coherent shared-memory system. For instance, the last-level TLB structures of two or more multiprocessor nodes can be configured to act together as either a distributed shared last-level TLB or a directory-based shared last-level TLB. Such TLB-sharing techniques increase the total amount of useful translations that are cached by the system, thereby reducing the number of page-table walks and improving performance. Furthermore, a coherent shared-memory system with a shared last-level TLB can be further configured to fuse TLB and cache misses such that some of the latency of data coherence operations is overlapped with address translation and data cache access latencies, thereby further improving the performance of memory operations.

Abstract: In a multi-chip module (MCM), integrated circuits are coupled by optical waveguides. These integrated circuits receive optical signals from a set of light sources which have fixed carrier wavelengths. Moreover, a given integrated circuit includes: a transmitter that modulates at least one of the optical signals when transmitting information to at least another of the integrated circuits; and a receiver that receives at least one modulated optical signal having one of the carrier wavelengths when receiving information from at least the other of the integrated circuits. Furthermore, the MCM includes tunable drop filters optically coupled to the optical waveguides and associated integrated circuits, wherein the tunable drop filters pass adjustable bands of wavelengths to receivers in the integrated circuits. Additionally, control logic in the MCM provides a control signal to the tunable drop filters to specify the adjustable bands of wavelengths.

Abstract: The disclosed embodiments provide a system that uses broadcast-based TLB-sharing techniques to reduce address-translation latency in a shared-memory multiprocessor system with two or more nodes that are connected by an electrical interconnect. During operation, a first node receives a memory operation that includes a virtual address. Upon determining that one or more TLB levels of the first node will miss for the virtual address, the first node uses the electrical interconnect to broadcast a TLB request to one or more additional nodes of the shared-memory multiprocessor in parallel with scheduling a speculative page-table walk for the virtual address. If the first node receives a TLB entry from another node of the shared-memory multiprocessor via the electrical interconnect in response to the TLB request, the first node cancels the speculative page-table walk. Otherwise, if no response is received, the first node instead waits for the completion of the page-table walk.