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Supporting Systolic and Memory Communication in iWarp

Supporting Systolic and Memory Communication in iWarp. CS258 Paper Summary Computer Science Jaein Jeong. Systolic array architecture. Replacing a processing element (PE) with an array of PE’s without increasing I/O bandwidth. Memory. Conventional. PE. Memory. Systolic. PE. PE. PE. PE.

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Supporting Systolic and Memory Communication in iWarp

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  1. Supporting Systolic and Memory Communication in iWarp CS258 Paper Summary Computer Science Jaein Jeong

  2. Systolic array architecture • Replacing a processing element (PE) with an array of PE’s without increasing I/O bandwidth Memory Conventional PE Memory Systolic PE PE PE PE PE

  3. CPU CPU CPU Local Mem Local Mem Local Mem CPU CPU CPU Local Mem Local Mem Local Mem Two communication styles • Systolic Communication:A CPU directly communicates through queues Memory Communication:Communication goes through local memory

  4. Memory communication • Pros • Cons • Application doesn’t need to know memory access detail. • Data can be accessed randomly. • Communication takes memory bandwidth • Long communication latency

  5. Systolic Communication • Advantages • Disadvantages • Fine grain communication due to reduced latency. • Reduced local memory access • Reduced size for local memory • Increased instruction-level parallelism • Hard to use – messages are accessed sequentially • Messages can’t be retransmitted

  6. iWarp communication • Program access to communication • Supports Systolic communication • Speeds up memory communication(Messages are transferred between user spaces) • A processor can alter a route and forward data to another processor without buffering. • Logical channels • Higher degree of connectivity by mapping multiple alogical channels over physical channels. • Guarantees communication bandwidth by time multiplexing logical channels.

  7. Logical Channels Computation Agent Me- mory Agent • Logical channels are mapped over physical buses using queues. • Once logical channelsare allocated, data is transmitted over the channels. • To prevent sending data to full queue, a sender counts free slots of receiver queue. Communication Agent

  8. Two types of logical channels • Reservation pool (implememted by pathway) • For transporting data for a long period of time. • A pathway is built and dismantled using special messages (pathway begin marker, end marker) • Each cell routes a message either by forwarding it to its neighbor or receiving it. • Open pool • For message passing of short period, No pathway

  9. Data and Control interface within a iWarp processor • Data interface b/w comp and comm • Reads/writes to gates access queues which are bound to corresponding logical channels. • Data interface to memory • FIFO like spooling gates are mapped between mem and comm or comp. • Memory can be used for extension of msg queue. • Control interface b/w comp and comm • Comp => comm : stores info in comm’s CAM. • Comm => comp : sets status register

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