11-05-2013, 02:40 PM
System Metrics and Pipelining
System Metrics.ppt (Size: 329.5 KB / Downloads: 166)
Amdahl’s Law
Architecture design is very bottleneck-driven – make the
common case fast, do not waste resources on a component
that has little impact on overall performance/power
Amdahl’s Law: performance improvements through an
enhancement is limited by the fraction of time the
enhancement comes into play
Example: a web server spends 40% of time in the CPU
and 60% of time doing I/O – a new processor that is ten
times faster results in a 36% reduction in execution time
(speedup of 1.56) – Amdahl’s Law states that maximum
execution time reduction is 40% (max speedup of 1.66)
Principle of Locality
Most programs are predictable in terms of instructions
executed and data accessed
The 90-10 Rule: a program spends 90% of its execution
time in only 10% of the code
Temporal locality: a program will shortly re-visit X
Spatial locality: a program will shortly visit X+1
Exploit Parallelism
Most operations do not depend on each other – hence,
execute them in parallel
At the circuit level, simultaneously access multiple ways
of a set-associative cache
At the organization level, execute multiple instructions at
the same time
At the system level, execute a different program while one
is waiting on I/O
Factors Determining Cost
Cost: amount spent by manufacturer to produce a finished
good
High volume faster learning curve, increased
manufacturing efficiency (10% lower cost if volume doubles),
lower R&D cost per produced item
Commodities: identical products sold by many vendors in
large volumes (keyboards, DRAMs) – low cost because of
high volume and competition among suppliers
Defining Fault, Error, and Failure
A fault produces a latent error; it becomes effective when
activated; it leads to failure when the observed actual
behavior deviates from the ideal specified behavior
Example I : a programming mistake is a fault; the buggy
code is the latent error; when the code runs, it is effective;
if the buggy code influences program output/behavior, a
failure occurs
Example II : an alpha particle strikes DRAM (fault); if it
changes the memory bit, it produces a latent error; when
the value is read, the error becomes effective; if program
output deviates, failure occurs