Intel Reveals New CPU Instructions, Enhanced Feedback Interface for Hardware (EHFI)

Intel up to date their programming reference guide this week with some attention-grabbing new additions, primarily round consumer interrupts and the improved {hardware} suggestions interface.

Whereas Intel has already disclosed AMX (Superior Matrix Extensions) as coming with Sapphire Rapids and another new directions, they’ve now disclosed extra directions which are on the best way. Some seem like coming with Sapphire Rapids whereas others on the shopper facet with Alder Lake. New Intel directions documented by this newest PRM revision embody CLUI, HRESET, SENDUIPI, STUI, TESTUI, UIRET, VPDPBUSD, VPDPBUSDS, VPDPWSSD and VPDPWSSDS.

Intel Reveals New CPU Instructions, Enhanced Feedback Interface for Hardware (EHFI)

The fast abstract of those new directions embody:

CLUI – Permits clearing the consumer interrupt flag instantly and in flip blocking consumer interrupts.

HRESET – Historical past reset to selectively reset the prediction historical past of the present logical processor. This reset request works for a number of predictions however what’s reset is partly managed by the working system / kernel in what bits it units for the HRESET MSR. Initially this permits resetting the EHFI (Enhanced {Hardware} Suggestions Interface) historical past however there are reserved bits for future growth.

SENDUIPI – This instruction permits sending consumer inter-processor interrupts.

STUI – Set Consumer Interrupt Flag.

TESTUI – Copying the present worth of the consumer interrupt flag.

UIRET – Consumer-interrupt return to return from dealing with a consumer interrupt.

VPDPBUSD – Multiply and including unsigned and signed bytes.

VPDPBUSDS – Multiplying and including unsigned and signed bytes with saturation.

VPDPWSSD – Multiplying and including signed phrase integers.

VPDPWSSDS – Multiplying and including signed phrase integers with saturation.

Numerous the directions revolve round consumer interrupts in getting used for brand new occasions within the structure at CPL 3. The brand new chapter outlines the structure in nice element.

The opposite attention-grabbing disclosure from this replace is on the Enhanced {Hardware} Suggestions Interface (EHFI). The Enhanced {Hardware} Suggestions Interface offers steering to the kernel’s scheduler on optimum process placement of workloads among the many logical processors. EHFI goals to assist the scheduler choose a CPU thread whether or not it’s aiming for the very best efficiency or highest power effectivity. It is going to be very attention-grabbing to see how this EHFI hardware-based scheduling works in follow and if its correct sufficient to ship vital efficiency/energy benefits in comparison with the present Linux kernel scheduler. With Intel’s hybrid structure in Alder Lake the kernel’s scheduler has extra to take care of and hopefully EHFI will work out nicely for optimum placement.

The up to date documentation additionally covers efficiency monitoring modifications which are coming for Alder Lake and Saphpire Rapids with new capabilities of the PMU.

The most recent revision of the Intel programming reference guide will be discovered at software for some attention-grabbing weekend studying.

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