What are the four states in MESI model and what are their roles?

The MESI protocol makes it possible to maintain the coherence in cached systems. It is based on the four states that a block in the cache memory can have. These four states are the abbreviations for MESI: modified, exclusive, shared and invalid.

How does MESI protocol work?

The MESI protocol is an Invalidate-based cache coherence protocol, and is one of the most common protocols that support write-back caches. This protocol reduces the number of main memory transactions with respect to the MSI protocol. This marks a significant improvement in performance.

What major advantage does the MESI protocol have over the write once protocol?

If MESI is implemented as a snooping protocol, then the main advantage over the three state protocol is when a read to an uncached block is followed by a write to that block. After the uncached block is read, it is marked “exclusive” – (need a scheme to know that it was uncached).

What does it happen with the capacity and coherence misses when you enlarge the number of processors?

What does it happen with the capacity and coherence misses when you enlarge the number of processors? Are there conflict misses in these experiments? Why? Answer The global miss rate will increase as the number of processor increases.

What is cache coherence problem and describe MESI protocol in brief?

In multiprocessor system where many processes needs a copy of same memory block, the maintenance of consistency among these copies raises a raises a problem referred to as Cache Coherence Problem. This occurs mainly due to these causes:- Sharing of writable data.

What is Copyback protocol?

The copy-back protocol is used. To copy the contents of the memory onto the cache. To update the contents of the memory from the cache. To remove the contents of the cache and push it on to the memory.

What is cache coherence problem and describe Mesi protocol in brief?

What is the advantage of Mesi over MSI?

The advantage of the MESI protocol over the MSI protocol lies in the fact that if the current cache has the Exclusive state, it can silently drop the cache block without issuing the expensive writeback operation. With the MESI protocol, the processor obtains the most current value everytime it is required.

How cache coherence problem is dealt in most of the cache system?

Cache coherence refers to the problem of keeping the data in these caches consistent. The main problem is dealing with writes by a processor. Write-through – all data written to the cache is also written to memory at the same time. Write-back – when data is written to a cache, a dirty bit is set for the affected block.

What are the 3 types of cache misses?

There are three basic types of cache misses known as the 3Cs and some other less popular cache misses.

• Compulsory misses.
• Conflict misses.
• Capacity misses.
• Coherence misses.
• Coverage misses.
• System-related misses.

What is cache coherence and cache coherence protocols?

In computer architecture, cache coherence is the uniformity of shared resource data that ends up stored in multiple local caches. Cache coherence is intended to manage such conflicts by maintaining a coherent view of the data values in multiple caches.

How do you solve cache coherence problem?

One approach is to use what is called an invalidation-based cache coherence protocol. This approach solves the cache coherence problem by ensuring that as soon as a core requests to write to a cache block, that core must invalidate (remove) the copy of the block in any other core’s cache that contains the block.