allow_frequency_scaling

Detailed Description

Lets an algorithm use the widest registers, despite frequency scaling.

Variables
constexpr auto	eve::algo::allow_frequency_scaling = ::rbr::flag( allow_frequency_scaling_tag{} )

Variable Documentation

allow_frequency_scaling

auto eve::algo::allow_frequency_scaling = ::rbr::flag( allow_frequency_scaling_tag{} )

inlineconstexpr

Header file #include <eve/module/algo.hpp>

namespace eve::algo
{
  inline constexpr auto allow_frequency_scaling = eve_implementation_defined;
}

Allows the algorithm to use the widest registers of the target. By default the cardinal stays clear of 512 bit registers, because some Intel cores lower their clock while AVX-512 instructions run and for a while after, which slows the scalar code that follows. With this trait the algorithm takes the full width, which is worth it on a long range only. The Frequency Scaling. tutorial measures the effect.

std::vector<float> data(1 << 20);
 
// A range this long amortises the clock drop, so the 512 bit registers win.
auto found = find_if[allow_frequency_scaling](data, [](auto x) { return x < 0.f; });

External references

• Travis Downs: Gathering Intel on Intel AVX-512 Transitions

See also

force_cardinal