Multi-core architectures - University of Southern ….ppt

Multi-core architectures;Single-core computer;Single-core CPU chip;Multi-core architectures;Multi-core CPU chip;The cores run in parallel;Within each core, threads are time-sliced (just like on a uniprocessor);Interaction with theOperating System;Why multi-core ?;Instruction-level parallelism;Thread-level parallelism (TLP);General context: Multiprocessors;Multiprocessor memory types;Multi-core processor is a special kind of a multiprocessor:All processors are on the same chip;What applications benefit from multi-core?;More examples;A technique complementary to multi-core:Simultaneous multithreading ;Simultaneous multithreading (SMT);BTB and I-TLB;Without SMT, only a single thread can run at any given time;SMT processor: both threads can run concurrently;But: Can’t simultaneously use the same functional unit;SMT not a “true” parallel processor;Multi-core: threads can run on separate cores;BTB and I-TLB;Combining Multi-core and SMT;SMT Dual-core: all four threads can run concurrently;Comparison: multi-core vs SMT;Comparison: multi-core vs SMT;The memory hierarchy;“Fish” machines;Designs with private L2 caches;Private vs shared caches?;Private vs shared caches;The cache coherence problem;The cache coherence problem;The cache coherence problem;The cache coherence problem;The cache coherence problem;The cache coherence problem;Solutions for cache coherence;Inter-core bus;Invalidation protocol with snooping;The cache coherence problem;The cache coherence problem;The cache coherence problem;The cache coherence problem;Alternative to invalidate protocol: update protocol;Which do you think is better? Invalidation or update?;Invalidation vs update;Invalidation protocols;Programming for multi-core;Thread safety very important;However: Need to use synchronization even if only time-slicing on a uniprocessor;Need to use synchronization even if only time-slicing on a uniprocessor;Assigning threads to the cores;Affinity masks are bit vectors;Affinity masks when multi-core an