expensiveoperations for today
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Here are a few examples of operations that are relatively expensive today:
- Network communication: even within a datacenter, a round-trip message exchange can take 10–50 µs, which is tens of thousands of instruction times. Wide-area round-trips can take 10–100 ms.
- I/O to secondary storage: disk I/O operations typically take 5–10 ms, which is millions of instruction times. Flash storage takes 10–100 µs. New emerging nonvolatile memories may be as fast as 1 µs, but this is still around 2000 instruction times.
- Dynamic memory allocation (malloc in C, new in C++ or Java) typically involves significant overhead for allocation, freeing, and garbage collection.
- Cache misses: fetching data from DRAM into an on-chip processor cache takes a few hundred instruction times; in many programs, overall performance is determined as much by cache misses as by computational costs.
Обратные ссылки
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