HyperThreading ● Improves processor performance under certain workloads by providing useful work...
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Transcript of HyperThreading ● Improves processor performance under certain workloads by providing useful work...
HyperThreading
● Improves processor performance under certain workloads by providing useful work for execution units that would otherwise be idle
● Duplicates sections of the processor
– those that store the architectural state
– does not duplicate main execution resources
● allows a physical processor to be two ”logical” processors
– can schedule two threads or processes simultaneously
When processor stalls
● as a result of
– cache miss
– branch misprediction
– data dependency
● processor may use those execution resources to
execute other processes or threads
Architectural State
● Control Registers
– instruction flag registers
– interrupt mask registers
– memory management registers
– status registers
● General purpose registers (AX, BX, CX, DX, ...)
Improved Performance
● Uses 5% of the die area over the “normal”
processor
● Performance improvements of up to 30%
Dual Core
● One which combines two or more independent
processors into a single package
● Contains two independent microprocessors
● Allows thread-level parallelism w/o including
multiple microprocessors in separate physical
packages
● CMP – chip level multiprocessing
Advantages vs SMP
● Cache coherency
– Can operate at a much higher clock rate than is
possible if the signals have to travel off-chip
● Less space required
● Less power usage
Disadvantages
● Requires OS support
● Requires threaded applications
● Integration of multi-core chip drives production
yields down, they are more difficult to manage
thermally than lower-density single-chiop