Virtual Labs

MSI Cache Coherence Protocol

What does the 'M' state represent in the MSI cache coherence protocol?

a: Memory state - data is only in main memory Explanation

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b: Modified state - cache line has been modified and is exclusive to this processor Explanation

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c: Multiple state - data is shared across multiple caches Explanation

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d: Master state - this processor controls all cache operations Explanation

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In a cache coherence protocol, what problem are we trying to solve?

a: Reducing memory access time for single processors Explanation

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b: Increasing cache size to store more data Explanation

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c: Ensuring consistent view of memory across multiple processors with private caches Explanation

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d: Optimizing cache replacement algorithms Explanation

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What does 'S' state mean in the MSI protocol?

a: Synchronized - all processors are synchronized on this cache line Explanation

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b: Stale - the data in cache is outdated Explanation

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c: Secure - the cache line is protected from modifications Explanation

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d: Shared - the cache line is unmodified and may be shared with other processors Explanation

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When a processor wants to read data that is not in its cache (cache miss), what bus transaction is typically issued?

a: BusWrite Explanation

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b: BusRd Explanation

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c: BusRdX Explanation

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d: BusInvalidate Explanation

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What happens to other processors' cache lines when a BusRdX transaction is observed on the bus?

a: They transition to Invalid state if they have the same cache line Explanation

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b: They transition to Modified state Explanation

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c: They remain unchanged Explanation

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d: They transition to Shared state Explanation

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In the MSI protocol, when does a cache line in Modified state transition to Shared state?

a: When the processor performs a write operation Explanation

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b: When another processor issues a BusRd for the same cache line Explanation

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c: When the cache line is accessed for reading locally Explanation

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d: When the processor is switched to a different task Explanation

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What is the primary advantage of bus snooping in cache coherence protocols?

a: It allows caches to monitor bus transactions and maintain coherence automatically Explanation

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b: It reduces the cache miss penalty Explanation

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c: It increases the cache size effectively Explanation

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d: It eliminates the need for main memory Explanation

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Consider two processors P0 and P1, both initially have cache line X in Shared state. If P0 wants to write to X, what sequence of events occurs?

a: P0 writes directly, P1's cache remains in Shared state Explanation

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b: P0 issues BusRdX, P1 invalidates its copy, P0 transitions to Modified Explanation

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c: Both processors transition to Modified state simultaneously Explanation

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d: P0 issues BusUpgr, P1 invalidates its copy, P0 transitions to Modified Explanation

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What is a potential performance problem with the basic MSI protocol?

a: False sharing can cause unnecessary invalidations and bus traffic Explanation

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b: It doesn't support multiprocessor systems Explanation

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c: It requires too much cache memory Explanation

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d: It cannot handle read operations efficiently Explanation

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