Intel Sapphire Rapids To Have Experimental "RAR" Feature

Written by Michael Larabel in Intel on 7 July 2021 at 06:18 AM EDT. 12 Comments
Adding to the lengthy list of features for Intel's next-gen Xeon "Sapphire Rapids" processors next year is an admittedly experimental feature called RAR, or Remote Action Requests.

Intel has publicly disclosed RAR this month in a new whitepaper as an experimental feature that will be found on Sapphire Rapids processors but not guaranteed for other future CPUs, depending upon feedback and usage from this model-specific feature with Sapphire Rapids it may be revised or even just eliminated in future processors.

Remote Action Requests amount to hardware-based TLB shootdowns for speeding up TLB shootdowns otherwise handled by the operating system. The goal of Remote Action Requests is to speed-up inter-process operations thanks to punting that work from software to hardware.

The RAR whitepaper notes, "RAR is used for speeding up remote TLB shootdowns and allowing them to be serviced while a long instruction is executing on the remote processor or when interrupts are disabled on that processor. RAR is architected to allow for future expansion."

Those interested in all the technical details of Remote Action Requests can see this whitepaper. At is more information on Intel's experimental features feedback focus. The whitepaper was just published and now presumably in short order Intel will be posting Linux patch(es) to allow using RAR on Sapphire Rapids processors.
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