System information
136 System Analysis and Tuning Guide
C-states and P-states can vary independently of one another.
11.1.3 T-States (Processor Throttling
States)
T-states refer to throttling the processor clock to lower frequencies in order to reduce
thermal effects. This means that the CPU is forced to be idle a fixed percentage of
its cycles per second. Throttling states range from T1 (the CPU has no forced idle cy-
cles) to Tn, with the percentage of idle cycles increasing the greater n is.
Note that throttling does not reduce voltage and since the CPU is forced to idle part of
the time, processes will take longer to finish and will consume more power instead of
saving any power.
T-states are only useful if reducing thermal effects is the primary goal. Since T-states
can interfere with C-states (preventing the CPU from reaching higher C-states), they
can even increase power consumption in a modern CPU capable of C-states.
11.1.4 Turbo Features
Since quite some time, CPU power consumption and performance tuning is not on-
ly about frequency scaling anymore. In modern processors, a combination of differ-
ent means is used to achieve the optimum balance between performance and power
savings: deep sleep states, traditional dynamic frequency scaling and hidden boost fre-
quencies. The turbo features (Turbo CORE* or Turbo Boost*) of the latest AMD* or
Intel* processors allow to dynamically increase (boost) the clock speed of active CPU
cores while other cores are in deep sleep states. This increases the performance of ac-
tive threads while still complying to Thermal Design Power (TDP) limits.
However, the conditions under which a CPU core may use turbo frequencies are very
architecture-specific. Learn how to evaluate the efficiency of those new features in
Section11.3.2, “Using the cpupower Tools” (page141).